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LMIs in Control/Click here to continue/Applications of Linear systems/An LMI for the Kalman Filter

This is a An LMI for the Kalman Filter. The Kalman Filter is one of the most widely used state-estimation techniques. It has applications in multiple aspects of navigation (inertial, terrain-aided, stellar.)

The System
Continuous Time:

\begin{align} \dot x(t)&=Ax(t)+Bu(t)+w(t),\\ y(t)&=Cx(t)+v(t)\\ \end{align}$$

The process and sensor noises are given by $$ w(t) $$ and $$ v(t) $$ respectively.

Discrete Time:

\begin{align} x_{k+1} &= Ax_k+w_k\\ y_k &= Cx_k +v_k \end{align}$$

The process and sensor noises are given by $$ w_k $$ and $$ v_k $$ respectively.

The Data
The data required for the Kalman Filter include a model of the system that the states are trying to be output and a measurement that is the output of the system dynamics being estimated.

The Filter
The Filter and Estimator equations can be written as:

Continuous Time

\begin{align} \dot \hat{x}(t) &= A\hat{x}(t)+Bu(t)+L(y(t)-\hat{y}(t))\\ \end{align}$$

Discrete Time

\begin{align} \hat{x}_{k+1} &= A\hat{x}_k + L(C\hat{x}_k-y_k)\\ \end{align}$$

The Error
The error dynamics evolve according to the following expression

Continuous Time

\begin{align} \dot e(t)&=(A+LC)e(t)+w(t)+Lv(t)\\ \end{align}$$

Discrete Time

\begin{align} e_{k+1}&=(A+LC)e_k + w_k + Lv_k\\ \end{align}$$

The Optimization Problem
The Kalman Filtering (or LQE) problem is a Dual to the LQR problem. Replace the matrices $$ (A,B,Q,R,K) $$ from LQR with $$ (A^T,C^T,V_1,V_2,L^T). $$

The Kalman Filter chooses $$ L $$ to minimize the cost $$ J = E[e^Te]. $$ This cost can be thought of as the covariance of the state error between the actual and estimated state. When the state error covariance is low the filter has converged and the estimate is good.

The Luenberger or Kalman gain can be computed from $$ L = \Sigma C^TV_2^{-1} $$

The process and measurement noise covariances for the Kalman filter are given by

\begin{align} V_1 &= E[w(t)w(t)^T] \text{ aka: } Q\\ V_2 &= E[v(t)v(t)^T] \text{ aka: } R\\ \end{align}$$

The matrix $$ \Sigma $$ satisfies the following equality

$$ A\Sigma + \Sigma A^T + V_1 = \Sigma C^TV_2^{-1}C\Sigma $$

We also cover the discrete Kalman Filter formulation which is more useful for real-life computer implementations.

The discrete Kalman filter chooses the gain $$ L = A\Sigma C^T(C\Sigma C^T+V)^{-1} $$ where the PSDs of the process and sensor noises are given by

\begin{align} W &= E[w_kw_k^T] \text{ aka: } Q\\ V &= E[v_kv_k^T] \text{ aka: } R\\ \end{align}$$

The steady-state covariance of the error in the estimated state is given by $$\Sigma$$ and satisfies the following Riccati equation.

\begin{align} \Sigma = A\Sigma A^T+W-A\Sigma C^T (C\Sigma C^T+V)^{-1}C\Sigma A^T \end{align}$$

 * Objective: State Estimate Error Covariance
 * Variables: Observer Gains
 * Constraints: Dynamics of System to be Estimated

The LMI: H2-Optimal Control Full-State Feedback to LQR to Kalman Filter
The Kalman Filter is a dual to the LQR problem which has been shown to be equivalent to a special case of H2-static state feedback.

Start with the H2-Optimal Control Full-State Feedback.

The following are equivalent

\begin{align} 1. ||S(K,P)||_{H2} &< \gamma\\ \end{align}$$

\begin{align} 2. K &= ZX^{-1} \text{ for some } Z \text{ and } X > 0 \text{ where} \\ \end{align}$$

\begin{align} [A \ B_2] \begin{bmatrix} X\\ Z\\ \end{bmatrix} + [X \ Z^T] \begin{bmatrix} A^T\\ B_2^T\\ \end{bmatrix} + B_1B_1^T < 0 \\

\begin{bmatrix} X & (C_1X+D_{12}Z)^T\\ C_1X+D_{12}Z & W \end{bmatrix} > 0 \\ TraceW < \gamma \\ \end{align}$$

To solve the LQR problem using H2 optimal state-feedback control the following variable substitutions are required.

\begin{align} C_1 = \begin{bmatrix} Q^{1/2}\\ 0\\ \end{bmatrix}, D_{12} = \begin{bmatrix} R^{1/2}\\ 0\\ \end{bmatrix}, D_{11} = 0, \\ B_2 = B, B_1 = I \end{align}$$

Then

\begin{align} S(P,K) = \begin{bmatrix} A+B_2K & B_1\\ C_1+D_{12}K & D_{11}\\ \end{bmatrix} = \begin{bmatrix} A+BK& I\\ Q^{1/2}& 0 \\K & 0\\ \end{bmatrix} \end{align}$$

This results in the following LMI.

\begin{align} [A \ B] \begin{bmatrix} X\\ Z\\ \end{bmatrix} + [X \ Z^T] \begin{bmatrix} A^T\\ B^T\\ \end{bmatrix} + I < 0 \\

\begin{bmatrix} X & (\begin{bmatrix} Q^{1/2}\\ 0\\ \end{bmatrix}X+\begin{bmatrix} R^{1/2}\\ 0\\ \end{bmatrix}Z)^T\\ \begin{bmatrix} Q^{1/2}\\ 0\\ \end{bmatrix}+\begin{bmatrix} R^{1/2}\\ 0\\ \end{bmatrix}Z & W \end{bmatrix} > 0 \\ TraceW < \gamma \\ \end{align}$$

To solve the Kalman Filtering problem using the LQR LMI replace $$A,B,Q,R,K$$ with $$A^T,C^T,V_1,V_2,$$ and $$L^T.$$ This results in the following LMI.

\begin{align} [A^T \ C^T] \begin{bmatrix} X\\ Z\\ \end{bmatrix} + [X \ Z^T] \begin{bmatrix} A\\ C\\ \end{bmatrix} + I < 0 \\

\begin{bmatrix} X & (\begin{bmatrix} V_1^{1/2}\\ 0\\ \end{bmatrix}X+\begin{bmatrix} V_2^{1/2}\\ 0\\ \end{bmatrix}Z)^T\\ \begin{bmatrix} V_1^{1/2}\\ 0\\ \end{bmatrix}+\begin{bmatrix} V_2^{1/2}\\ 0\\ \end{bmatrix}Z & W \end{bmatrix} > 0 \\ TraceW < \gamma \\ \end{align}$$

The discrete-time Kalman Filtering LMI is saved for another page as it requires derivation of the Discrete-Time LQR LMI problem which was not covered in class.

Conclusion:
The LMI for the Kalman Filter allows us to calculate the optimal gain for state estimation. It is shown that it can be found as a special case of the H2-optimal state feedback with the appropriate substitution of matrices. The LMI gives us a different way of computing the optimal Kalman gain.

Implementation
A link to CodeOcean or other online implementation of the LMI

Related LMIs
Links to other closely-related LMIs

 * H2OptimalObserver


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LMIs in Control/Click here to continue/Applications of Linear systems/Hinf Optimal Model Reduction

Given a full order model and an initial estimate of a reduced order model it is possible to obtain a reduced order model optimal in $$

H_{\infty} $$ sense. This methods uses LMI techniques iteratively to obtain the result.

The System
Given a state-space representation of a system $$

G(s) $$ and an initial estimate of reduced order model $$

\hat{G}(s) $$.

\begin{align} \ G(s) &= C(sI-A)B + D,\\ \ \hat{G}(s) &= \hat{C}(sI-\hat{A})\hat{B} + \hat{D},\\ \end{align}$$

Where $$ A \in \mathbb{R}^{n\times n}, B \in \mathbb{R}^{n\times m}, C \in \mathbb{R}^{p\times n}, D \in \mathbb{R}^{p\times m}, \hat{A} \in \mathbb{R}^{k\times k}, \hat{B} \in \mathbb{R}^{k\times m}, \hat{C} \in \mathbb{R}^{p\times k}$$ and $$\hat{D} \in \mathbb{R}^{p\times m}$$. Where $$ n,k,m,p $$ are full order, reduced order, number of inputs and number of outputs respectively.

The Data
The full order state matrices $$ A,B,C,D $$ and the reduced model order $$ k $$.

The Optimization Problem
The objective of the optimization is to reduce the $$ H_{\infty} $$ norm distance of the two systems. Minimizing $$ \|G - \hat{G}\|_{\infty}$$ with respect to $$ \hat{G} $$.

The LMI: The Lyapunov Inequality
Objective: $$ \min \gamma $$.

Subject to:: $$

\begin{align} \ P &= \begin{bmatrix} \ P11 & P12 \\ \ P21 & P22 \\ \end{bmatrix} \ > 0, \end{align} $$

$$ \begin{align} \begin{bmatrix} \ A^{T}P11 + P11A & A^{T}P12 + P12\hat{A} & P11B - P12\hat{B} & C^T \\ \ \hat{A}^{T}P12^T + P12^{T}A & \hat{A}^{T}P22 + P22\hat{A} & P12^{T}B - P22\hat{B} & \hat{C}^T \\ \ B^{T}P11 - \hat{B}^{T}P12^{T} & B^{T}P12 - \hat{B}^{T}P22 & -\gamma{I} & D^{T} -\hat{D}^{T} \\ \ C & \hat{C} & D -\hat{D} & -\gamma{I} \\ \end{bmatrix} \ > 0 \end{align}$$

It can be seen from the above LMI that the second matrix inequality is not linear in $$ \hat{A}, \hat{B}, \hat{C}, \hat{D}, P $$. But making $$ \hat{A}, \hat{B}$$ constant it is linear in $$ \hat{C}, \hat{D}, P $$. And if $$ P12, P22 $$ are constant it is linear in $$ \hat{A}, \hat{B}, \hat{C}, \hat{D}, P11 $$. Hence the following iterative algorithm can be used.

(a) Start with initial estimate $$ \hat{G} $$ obtained from techniques like Hankel-norm reduction/Balanced truncation.

(b) Fix $$ \hat{A}, \hat{B}$$ and optimize with respect to $$ \hat{C}, \hat{D}, P $$.

(c) Fix $$ P12, P22 $$ and optimize with respect to $$ \hat{A}, \hat{B}, \hat{C}, \hat{D}, P11 $$.

(d) Repeat steps (b) and (c) until the solution converges.

Conclusion:
The LMI techniques results in model reduction close to the theoretical limits set by the largest removed hankel singular value. The improvements are often not significant to that of Hankel-norm reduction. Due to high computational load it is recommended to only use this algorithm if optimal performance becomes a necessity.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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LMIs in Control/Click here to continue/Applications of Linear systems/An LMI for Multi-Robot Systems

LMIs in Control/Applications/An LMI for Multi-Robot Systems/Consensus for Multi-Agent Systems

This application gives an instance of the use of LMIs in achieving consensus for multi-agent systems. More focus is placed on the flocking algorithm, which is one of the consensus algorithms extensively used in multi-robot systems.

Introduction
A robot swarm is a network of multiple robots working together as a unit to achieve an objective. In order for robots in a swarm to work together, they need to come to consensus/agreement on a number of parameters. A number of algorithms called consensus algorithms exist to serve that purpose. Consensus Algorithms are algorithms that allow a set of agents to reach an agreement. Various areas such as graph theory, control theory and matrix theory overlap when it comes to designing consensus algorithms for multi-agent systems.

Flocking Algorithm
The flocking algorithm is one of the consensus algorithms used in trajectory planning for multi-agent networks. The algorithm helps in maintaining separation, so that the agents do not collide, alignment, so that the agents have the same headings, and cohesion, so that the agents do not wonder far away from each other. The flocking algorithm can be represented in a graph network form, where the nodes in the graph represent the agents or individual robots, and the edges/links represent the nature of interaction between the nodes. Consequently. the interactions between the nodes can be Below is the general equation for a flocking algorithm.

$$\dot {v_i}-\sum_{ i=N_i}^n i = (v_i - v_j) + \sum_{ i=N_i}^n i \Delta_{r_i} V_{ij} (r_{ij})$$, where

$$V_{ij}$$ is the artificial potential function

$$n $$ is the number of robots

$$\dot {v_i}$$ is the input/acceleration control

$$r_{i}$$ is the position vector of robot $$i$$

$$r_{ij} = r_i - r_j$$, which is the distance between two neighboring robots

Mathematical Model:
Before we begin, we need to obtain a state space representation for our system. Based on observation, it can be deduced that the general form of a consensus algorithm bears some resemblance to the state space equation. The general equation for a consensus algorithm in terms of the Laplacian matrix is:

$$\dot{x} = -Lx$$, where $$L$$ represents the Laplacian matrix.

Comparing the above equation to the state space equation, $$\dot{x} = Ax$$, we notice that the $$A$$ has been substituted with a $$-L$$.

The A, B and C matrices are represented as diagonal blocks because of the decentralized nature of the control framework. Each block in the A, B and C matrices is associated with its corresponding state, input, or output vector.

$$

\begin{align} \ A &= \begin{bmatrix} \ a_{11} & a_{1n} \\ \ a_{n1} & a_{nn} \\ \end{bmatrix}&

\ B = \begin{bmatrix} \ b_{11} & b_{1n} \\ \ b_{n1} & b_{nn} \\ \end{bmatrix}&

\ &C = \begin{bmatrix} \ c_{11} & c_{1n} \\ \ c_{n1} & c_{nn} \\ \end{bmatrix} \end{align} $$

x, u and y represent the state, input and output vectors respectively.

$$

\begin{align} \ x &= \begin{bmatrix} \ x_1 & ... &x_n \\ \end{bmatrix}^T &

\ y &= \begin{bmatrix} \ y_1 & ... &y_n \\ \end{bmatrix}^T &

\ u &= \begin{bmatrix} \ u_1 & ... &u_n \\ \end{bmatrix}^T & \end{align} $$

Further Discussion:
In Elham Semsar-Kazerooni and Khashayar's paper, "Optimal Consensus Seeking in a Network of Multi-Agent Systems", further work was done through a series of variable substitutions and other mathematical operations to obtain the an LMI as seen below. For more information on the LMI formulation procedure, and the details of the variables in the above LMI, please visit follow the link in the reference section to review the paper.

Objective: $$ \min trace(P) $$.

Subject to::

$$ \begin{align} \ \begin{bmatrix} \ \gamma & \bar{S}^*ZQ^{1/2} & \bar{S}^*W^*R^{1/2} \\ \ Q^{1/2}Z \bar{S} & -I & 0 \\ \ R^{1/2}W \bar{S} & 0 & -I \\ \end{bmatrix} \ < 0, \end{align}

$$


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LMIs in Control/Click here to continue/Applications of Linear systems/Helicopter Inner Loop LMI

This is a Helicopter Inner Loop LMI. Optimization methods and optimal control have had difficulty gaining traction in the rotorcraft control law community. However, this LMI derived in the referenced paper attempts to address the issues with a LMI for Robust, Optimal Control.

The System
Continuous Time:

\begin{align} \dot x(t)&=\hat{A}x(t)+B_1w(t)+\hat{B_2}u(t),\\ z(t)&=C_1x(t)+D_{12}u(t)\\ \end{align}$$

The Helicopter model is given by knowledge of the stability and control derivatives which populate the elements of the $$ \hat{A}, \hat{B_2} $$ matrices in the dynamic equations above.

The state vector is given by the typical elements of a rigid 6-DOF body model. $$ x = \begin{bmatrix} u,w,q,\theta,v,p,\psi,r\end{bmatrix}^T $$. The input vector is given by $$ u = \begin{bmatrix}\delta_0,\delta_{1s},\delta_{1c},\delta_T\end{bmatrix}^T $$ which pertain to the main rotor collective, longitudinal/lateral cyclic and tail rotor collective blade angles in radians.

The gust disturbance is denoted by $$w(t)$$ and is assumed to be random in nature. The stability and control derivative matrices are modeled with uncertainty as follows:

\begin{align} \hat{A} = A + \Delta A, \hat{B_2} = B_2 + \Delta B\\ \end{align}$$

The $$\Delta $$ terms represent the uncertainties in the helicopter system model.

The Data
The Data required for this LMI are the stability and control derivatives that populate the A and B-matrices of the system above which can be obtained from linearizing non-linear models. It can also be obtained from experimental methods such as step responses and swept sines (System Identification.)

The Control Architecture
A control architecture for the inner loop of the helicopter model mentioned above is designed using a state feedback control law.

$$u = Kx(t) $$

The objective for the inner loop control is to design a full state feedback law such that the closed-loop helicopter system satisfies the following 3 performance specifications.

The Optimization Problem
Objective 1: The closed-loop system is internally stable for any admissible uncertainty.

Objective 2: Poles of the close-loop system lie within the disk $$ D(-q,r)$$ with center $$-q+j_0$$ and radius $$r, q>r>0$$, for any admissible uncertainty.

Objective 3: Given gust disturbance suppression index $$\gamma$$, for any admissible uncertainty, the effect of the gust disturbance to selected flight states and control input is in the given level, i.e.

$$\int_0^{\infty} \! \{x^T(t)Qx(t)+u^T(t)Ru(t)\} \ \mathrm{d}x < \gamma^2\int_0^{\infty} \! w(t)^Tw(t) \, \mathrm{d}t.$$

where $$w(t)\in L_2(0,\infty).$$ $$Q$$ and $$R$$ are weighting matrices with appropriate dimensions and $$Q=Q^T \geq 0, R = R^T>0.$$

It can be shown that the inner loop performance specifications listed in Objectives 1-3 can be met with a state feedback control law if the LMI described in the following section is true.

 * Objective: Objectives listed above
 * Variables: Controller Gains
 * Constraints: Rotorcraft Dynamics and Modeled Actuator Limits

The LMI: H-Inf Inner Loop D-Stabilization Optimization
The paper derives and LMI of the form below and asserts that the if there exists a constant $$\epsilon$$, matrix $$Z$$ with appropriate dimensions and a symmetric positive matrix $$P$$, such that

\begin{align} \\

\begin{bmatrix} \Psi_{11} & B_1 & XC_1^T+Z^TD_12^T & A_{\alpha}X_+B_2Z & XF_1^T+Z^TF_2^T & \epsilon H \\ B_1^T & -\gamma ^2 I & 0 & 0 & 0 & 0 \\ C_1X+D_{12}Z & 0 & -I & 0 & 0 & 0 \\ XA_{\alpha}^T + Z^TB_2^T & 0 & 0 & -rX & XF_1^T+Z^TF_2^T & 0 \\ F_1X+F_2Z & 0 & 0 & F_1X+F_2Z & -\epsilon I & 0 \\ \epsilon H^T & 0 & 0 & 0 & 0 & -\epsilon I \end{bmatrix} < 0 \\

\end{align}$$ where, $$\Psi_{11} = A_{\alpha}X+XA_{\alpha}^T+B_2Z+Z^TB_2^T,A_{\alpha}=A+\alpha I $$

This LMI is shown to satisfy Objectives 1, 2,3, and the control law is given by

\begin{align} u(t) = Kx(t)\\ K = ZX^{-1} \end{align} $$

Conclusion:
The LMI for Helicopter Inner Loop Control design provides an optimization-based approach towards achieving Level 1 Handling Qualities per ADS-33E. This is an interesting way to approach a very difficult problem that has usually been approached through classical control methods and with extensive piloted simulation and flight test.

Implementation
A link to CodeOcean or other online implementation of the LMI

Related LMIs
Links to other closely-related LMIs

 * Optimal_Output_Feedback_Hinf_LMI


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History of wireless telegraphy and broadcasting in Australia/Topical/Publications/Radio in ANZ/Issues/1923 05 16

Link to Issue PDF
WorldRadioHistory.com's scan of Radio in Australia and New Zealand - Vol. I No. 04 - 16 May 1923 has been utilised to create the partial content for this page and can be downloaded at this link to further extend the content and enable further text correction of this issue: Radio in ANZ 1923 05 16

In general, only content which is required for other articles in this Wikibook has been entered here and text corrected. The material has been extensively used, inter alia, for compilation of Biographical articles,  Radio club articles and  Station articles.

Front Cover
Issued every second Wednesday — Sixpence

RADIO IN AUSTRALIA & NEW ZEALAND — incorporating "Sea, Land and Air"

VOL I. — MAY 16, 1923 — No. 4

(Start Graphic Description) MUSIC IN THE AIR. The above photograph shows Miss Jeanette Vreeland, opera singer, and Bert Acosta just before they entered the 'plane, piloted by Lieut. Belvin Maynard. During the flight Miss Vreeland sang several songs into a radio transmitter, in aid of a collection for the American, Legion.— Underwood Photo (End Graphic Description)

Registered at G.P.O., Sydney, for transmission by post as a newspaper.

P.73 - Contents Banner
RADIO in AUSTRALIA & NEW ZEALAND Incorporating "Sea, Land and Air"

Managing Editor: S. E. TATHAM       Associate Editor: M. DIXON

CONTENTS

Volume I.  MAY 16, 1923    Number 4

P.73 - Contents
CONTENTS.

 * Radio Concert Cheers Patient in Hospital . . . Page 74
 * Radiotorial . . . Page 75
 * Radio's Proud Record . . . Page 76
 * Direction and Position Finding by Wireless . . . Page 77
 * An Expanding Radio Set . . . Page 80
 * Wireless Telephone "Call" . . . Page 82
 * The Experimenters' Corner . . . Page 84
 * Technical Terms . . . Page 86
 * Condenser as Waiting Room for Electrons . . . Page 87
 * Wireless Aid to Injured . . . Page 89
 * Call Letters . . . Page 90
 * Antenna . . . Page 90
 * Movements of Wireless Officers . . . Page 91
 * Weather Reports by Radio . . . Page 92
 * Radiofun . . . Page 93
 * Club Notes and News . . . Page 94
 * Long Wave Stations . . . Page 95
 * Queries Answered . . . Page 96

P.73 - Publication Notes
Published by: THE WIRELESS PRESS, 97 CLARENCE ST., SYDNEY; 422-24 Lt. Collins St., Melbourne; Australasia Chambers, Wellington, N.Z.

PRICE, 6d. per Copy; Subscription Rate, 10/- per annum (26 issues) throughout Australia and New Zealand; Foreign Rate, 12/6 (26 issues)

OVERSEAS REPRESENTATIVES:

Canada and United States of America: The Wireless Press Inc., 326 Broadway, New York City

Great Britain: The Wireless Press Ltd., 12-13 Henrietta St., London, W.C.2

P.74 - Radio Concert Cheers Patient
(Start Photo Caption) THE above photograph shows a patient in the emergency Hospital at Washington listening to a radio concert while undergoing an operation. The American doctors recognise that radio music is a remarkable tonic in the case of sick people. The very novelty of being able to listen to the cheerful strains of music while submitting to the gentle operations of the surgeon's knife is calculated to lift the sufferer's mind above his immediate surroundings. Of course music could be heard only when a patient was undergoing an operation by local anaesthetic, but both before and after operations of the most serious nature radio music is proving of immense value in cheering up patients whose state of mind would otherwise be most despondent. One naturally wonders how long it will be before patients in Australian Hospitals will be able to enjoy radio music the same as their American cousins.(End Photo Caption)

P.75 - Radiotorial
Broadcasting Speeches

LIMITED vision must be credited to those news- . papers and individuals who made light of the suggestion put forward by Dr. Stopford, M.L.A., President of the Balmain Radio Society, that a transmitting set should be installed at Sydney Parliament House to enable members' speeches to be broadcasted to ,"listeners in" all over the State. It is only fair to say, however, that the majority of critics cast no doubt on the practica.bility of doing as Dr. Stopford suggested-rather did they ridicule the idea that anyone wished to hear more of members utterances than they now read in the press. This, it may be allowed, is a debatable point, but if it were t1'ue that the speeches of members of Parliament are ns uninteresting and devoid of common-sense as some prople allege it would be a regrettable state of affairs. Personally we do not subscribe to that belief at all, and we feel confident that in the near future, probably during the life of the present Parliament, debates conducted on the floor of the House will be available to all who possess receiving sets no matter how remotely they may be located. Candidly speaking, the effect of a broadcasting service, even if it includes parliamentary debates, cannot £ail to be of great educational value. No intelligent person disputes the value of newspapers and other forms of literature in broadening people's minds and enabling them to obtain a more intelligent grasp of Speeches the leading questions of the day. It can safely be left to the good taste of the community to choose the reading matter it needs just the same as we can rely upon the "listeners in" to hang up their receivers if the. programme they are listening to fails to interest or amuse them. The fact that the broadcasting of parliamentary debates in Australia would be an innovation is no argument against undertaking it. Election campaigns have been conducted by radio in parts of America, and the possibility that a similar thing will happen here in the next couple of years is a very real one. It follows as a natural consequence that if the public are prepared to listen to a medley of voices proclaiming the virtues of their respective owners in an election fight they are not at all likely to object to hearing the words of wisdom which fall from the lips of our legislators on the floor of the House. It is not blind faith, but a knowledge of its wonderful ut.ility which induces enthusiasts like Dr. Stopford to advocate thr more general application of radio telephony to the needs of the general public. There is little doubt but that when the man in the street gets to know its value as a medium of communication and entertainment he will embrace it with an enthusiasm transcending that which greeted the telephone, gramophone and other inventions of first-hand importance.

Mankind's Debt to Radio

SCARCELY a week passes without some fresh evidence being adduced of the practical value of wireless telegraphy. It may seem a small thing in its way to read of a rescue party being directed to the scene of a shipwreck through the broadcasting of an S.O.S. call, or medical advice being flashed across a thousand miles of ocean to a sick or injured man, but it is points like these that count. Their true significance can only be realised by totalling up the countless human lives that have been saved, and the anxiety and 1mffering that have been obviated in recent years. Spurred on by the knowledge that every advancement 11lade in perfecting apparatus for the speedy and efficient transmission and reception of radio messages adds Rti]l further to its value to mankind, those engaged in exploiting the possibilities of wireless transmission vi sound may be expected to accomplish much useful work as time goes on. No greater incentive to work can be given any man than the knowledge that the whole world stands to benefit by his success, and it is safe to say that no discovery of ancient or modern times holds such possibilities for universal application of a high and useful order as radio telegraphy and telephony. With such a happy combination can it be wondered that all connected ,vith the enterprise view the future through rose-coloured spectacles? The day of pioneering the science is almost past; it has established its claim to be regarded as an agency of humanitarian and commercial value almost bevond estimation, and the future may he regarded as at its feet.

P.76 - Robbing the Sea of Its Terrors
'''Radio's Proud Record. Robbing the Sea of Its Terrors. Summit of Splendid Service.'''

I 'l' is a well-recognised fact t~at maritime disasters, of which there is a record from the time that man first attempted to cross the ocean in a frail craft, will continue so long as Nature makes war on man's creations by storms, fogs and other dangers which imperil life at sea. Much has been accomplished in recent years towards ensuring the safety of ocean travel. Larger and stouter vessels have been built, the introduction of various life-saving devices on board ship has been made compulsory, and signal stations have been established at various danger points along the Coast. Despite all these precautions, we are frequently alarmed, and sometimes saddened, by the news that ais3ister has befallen an ocean-going vessel. It is no evidence of human incompetence to have to make this admission; it simply reveals the operation of a law which is as inevitable as the setting sun, viz., that in many directions man's work must always fall helpleRs before the onslaughts of Nature. Radio Spells Safety. Fortunately, however, while it rn not always possible to prevent accidents, a cure can frequently be prescribed. It has been demonstrated on countless occasions during recent vears that radio telegraphy is re~ ponsible for saving more lives when a shipping disaster occurs than any other agency which can be called on to assist. The number of vessels that are regularly proceeding to and fro along the recognised routes spells almost certain rescue should a disaster occur in the vicinity, provided news of the happening reaches other ships. Radio telegraphy represents the only means of doing this, and it has done it so frequently and with such happy results, that its value is known to all. llistances Recalled. Who does not remember the mag-

nificent rescue work carried out by H.M.A.8. Melbourne when she responded to the S.O.S. call of the Helen B. Stirling. It is beyond question that had the helpless vessel not possessed a wireless outfit she, too, would have been added to the list of ocean mysteries. To mention another

meritorious rescue we can turn to the stranding of the Mindini on Mellish Reef. A rescue ship was speedily on the scene in response to a wireless call, and the passengers and crew were spared the ordeal of. spending several weeks on a shelterless island · under conditions which would almost certainly have resulted in the outbreak of disease. Yet another happening of recent date in which wireless telegraphy performed excellent service was the stranding of the Iron Prince at Cape Howe. The speed at which messages passed between the ship and the agents through medium of the Sydney Radio Station stands aR a tribute alike to the system and the men who operated it. Wreck of '' Iron Prince. '' As already mentioned, an excellent performance in the speedy exchange of messages stands to the credit of the operators at Sydney Radio, and on the ill-fated vessel immediately the disaster occurred. Mr. J. A. Guy, wireless officer on the Iron Prince, transmitted news of the vessel 's plight at 1.55 a.m. 011 the morning of April 19. The message was picked up by the operator on duty at Sydney Radio (Mr. W. C. H . Hodges), and within the space of one minute was despatched to Sydney, where it was communicated to Mr. Scott F ell, representing the Sydney agents. Mr. Fell unmediately got into direct touch with Pennant Hill by telephone, and in response to his request a message was transmitted to the Iron Prince. The answer was received and communicated to Mr. Fell while he held the telephone line-the whole operation occupying approximately sixty seconds. It is no ex· aggeration to say that the feat is one worthy of the highest commendation, and all concerned have every reason to feel proud of their achievement.

(Start Photo Caption) Mr. John A. Guy, Wireless Operator of the ill-fated steamer "Iron Prince." (End Photo Caption)

(Start Photo Caption) Mr. W. C. Hodges, Wireless Operator at Sydney Radio Station, who was on duty when the "Iron Prince" called for assistance. (End Photo Caption)

P.77 - Direction and Position Finding by Wireless
'''Direction and Position Finding by Wireless. Record of Progress.''' By George Apperley (Radio Engineer)

HE real practical application of · the Wireless Direction Finder was made ch~ring the Great War when its usefulness was abundantly proved. Its value in lo· eating enemy wireless installations ashore and afloat and in guiding aircraft cannot be over-estimated, and the result of the accumulated fund of information which became available as a result of its constant · nse day ancl night in actual servir'.es has Iead to remarkable developments: in this branch of wireless telegraphy. It has therefore, very rapidly emerged from the experimental stage to one where its practicability is firmly established. Hertz :in his ,·original researches showed that electromagnetic waves could be reflected in the same way as rays of light by the use of suitable cylindrical parabolic mirrors and also demonstrated that the amount 6f energy induced in his resonator rnriecl with its orientation in respect to the source of the radiated energy. The problem of directive transmission and reception of electromagn'"tic waves has since received the attention of many inventors, but until recent ?ears this branch of radio remaiaed more or less undeveloped. Marconi iu his early experiments in 18H9 successfully projected a beam of elt>etrie radiation in a given directi011

over a distance of about two miles by the method originally employel1 by Hert½ whilst snbseqUfmtly othei• inventors proposed using spaced vertical wires or screens arranged as reflectors in place of the mirrors. For the reason that waves which can be transmitted by reflectms ~of this nature are very limited in length, tlll' application of this method took no practical form until quite recently, and although at the present time it is being very usefully and extensively employed for transmission, its field of use is still limited to short distane\'s. Sloping antennae, revolving screens, and certain forms of rod oscillators were also suggested, but the first really practical solution of the problem was, however, due to Marconi. who, in 1905 employed bent antennae for both directional transmission and reception. Each antennae was constructed ill the form of an inverted [, the .horizoutal limb being made considerably longer than the vertical portion. He found that the transmission and reception qualities of such

antennae were greatest in a direction opposite to that in which the horizontal limb ,ms pointing, although transmission or reception could be effected to a less extent, in other direction:-;. 'rhis invention forms the subject matter of Commonwealth Letters Patent No. 5429/ 06, granted to Marconi's ,vireless 'l'elegraph Company Limite(1 of London. In 1906 Marconi patented in Great Britain a mPthod of employing a stellate receiving · aerial consist~ng of a number of bent antennae arranged radially from a central point for the purpose of locating the direction of any sending station. A receiver was arranged to be connected to each aerial in turn and the one which gave loudest. signals indicated that the transmitting station ,vas in a direction opposite to that in which its free end was pointing. During the same year F. Braun devised a method of directional transmission employing three simple antennae in which oscillations were created, having certaill definite phase differences by which means it was possible to cause the . waves emitted from each antennae to assist one another in certain directions lmt to neutralise each otlw!· -in certain other clirectiom,. This method

was not, however, as simple and practicable as the Marconi bent antennae. In 1907, E. Bellini and A. Tosi obtained a patent for a very pritetica1 system of directive radiotelegraphy employing nearly closed loop;,. The aerial system was suspended fr.)m a suitahle mast, and consisted of tw,, wires, the upper ends being immhttcc1 and the lower ends connected to tte transmitting or receiving instrnment8. The wires were stretched out to form a triangular loop. It is now well known that an oscillating circuit thus formed is capable of maximum radiation or reception of electro-magnetic waves when their direction of propagation lies in the plane of the loop, and minimum when at right angles to the plane. The radiation or reception qualities for other directions is shown in the figure-of-eight polar diagram L. Fig 1. As the inventors point out in Commonwealth Patent Specification No. 10060/ 07 of the invention, loops of this nature would satisfy! the requirements of fixed stations, but obviously if transmission or reception is req1;1_ired to be effected in all directions either the aerial loops must be constructed to rotate or a large number of them provided at each station. Both these methods are impracticable or inconvenient. The above Commonwealth Patent Specification of the invention of Bellini and Tosi describes a method of achieving this by employing two triangular loops fixed at right angles to each other as shown in Fig. 2. The bases of the two loops are connected each through a winding marked fild coil a and b. "RADIO" When the loops are influenced by electromagnetic waves radiated from a transmitting statio~ oscillating currents will flow in each and through the respective field windings the in,~ tensity of each current depending upon the angle between the direction of the transmitting station and the plane of the loop. Each current flow will give rise to a magnetic field · in the space limited by the field coils and produce a resultant field the direction of which will depend on the phasing and intensity of the two currents and consequently on the direction of the transmitting station. For the purpose of ascertaining the direction of the resultant field a third winding termed a sea,rch coil is placed inside the field windings and pivoted to rotate as shown in Fig. 3. The search coil may be connected to a detector of electromagnetic waves, and if rotated continuously during the time the aerial loops are influenced by a transmitting station, two points 180 degrees apart can be found where signals will be received with maximum intensity, and another two similarly separated, but at right angles to the former where signals cannot be heard. Directional transmission may also be carried out with such an arrangement by energising the search coil, the direction of transmission being varied at will by rotating the coil. The foregoing is the basic feature embodied in the greater number of modern Wireless Direction Finders at present in use. Other methods involving the use of one or more rotating aerial loops supported on suitable frames also find application in par- D.F. STAND Bl. May 16, 1923. ticular circumstances, but the sphere of usefulness is limited by the space required, and time occupied in rotating the loops when rapid readings are . required. In 1908 Bellini and Tosi applied for and were granted a patent in Australia, No. 13912/09 for an important improvement in their system whereby transmission or reception can be carried out solely in one direction. Hitherto, waves could be transmitted in any desired direction, but radiation also took place in the diametrically opposite direction, figure-ofeight polar diagram L, Fig. 1. Similarly it was possible to determine the line along which the waves arrived at the receiving station, but not possible to ascertain the direction along that line of the transmitting station. By combining a uniformly radiating aerial system such as a vertical wire with tp.e system of loop aerials shown in Fig. 2, they showed how signals may be transmitted to or received from any one point along a line passing through the vertical axis of the aerial system. The uniform transmitting and receivmg qualities 1of a vertical aerial are shown by the circular polar curve, V Fig. 1, and those of the loop aerials by the figure-of-eight. The vertical or uniformily radiating or receiving aerial is combined ·with the loop aerials so as to be · substantially in their symmetrical axic and magnetically coupled to the r eceiving system S, SI, R, as shown in Fig. 4, which is reproduced from the patent specification. When electromagnetic waves act on this arrangement oscillating currents I are1 :PTOTO

duced in each of the two aerials and act simultaneously on the receiver. If these two currents are equal in strength and in phase the signals in the receiver will be a maximum. If now a transmitting station is moved in a circle around the receiving system the intensity and phase of the current in the vertical aerial will remain uniform whilst that in the loop will have two maxima a.nd two minima with a change of phase through 180 degrees. Therefore; if the two currents are brought into phase they add when the transmitter is in the plane of the loop on one side, and when completely out of phase neutralise if the transmitter is in the plane of the loop on the other side. The resultant effect is shown by the "Heart shape" polar diagram H in Fig. 1. If, therefore, the absolute direction of any one transmitting Rtation is known or first ascertained the absolute direction of any othe~ unknown stations may be readily determined. The method of operation however, presented many practical difficulties owing to the necessity of very accurately tuning the aerials in order that the currents induced in each might bear the correct phase relationship. This difficulty i;, readilv obviated by a system of tuning i~vented in 1919 by H. J. Round and G. M. Wright, Commonwealth Letters Patent No. 15463/20 in which closed aerials having themselves no definite natural period are connected to field coils very cfosely coupled to ',the search coil. All necessary tuning of the aerials: may then be made by varying a capacity associated with the search coil circuit. In order to obtain maximum coupling the search coil is made with as large a diameter as possible so that it,; windings and those of the field coils are brought sc close together. Owing to the fact that the magnetic field produced by the field coils is not uniform, but is more intem:e in the neighbourhood of the· conductors themselves, errors are produced with such an arrangement because when the search coil is rotated the law of coupling between it and each field coil does not follow. the theoretically required sine ·la.w. In 1920 G. M. Wright devised a method for eliminating these errors employing a search coil wound in two sections displaced on the former by an angle of 45 degrees for which he was granted Commonwealth Letters Pa.tent No. 1707 /21. ., . In modern Directfo\1 ,,Finders employing the Bellini-Tosi typ{. of loop aerials, the vertical antenna. is dispensed with and the loop aerial system itself earthed at the central point•.of each field coil as shown in Fig. 2. .rin the earth connection may be included tuning elements and the system will then possess the uniform receivinO' aualities of a simple vertical wir: By suitably coupling this circuit to Page 79 the receiving circuit and introducing means for obtaining 1the necessary phasing of currents in the loops and earthed circuit the system will be capable of '' Heart Shape' ' reception as previously explained. Marconi's Wireless Telegraph-- Co. of London has extensively developed this system and produced a combination of apparatus free from the many defects which previously existed. The aerial loops are aperiodic and closely coupled to the receiving circuit for reasons already explained. Fig. 5 is a simplified diagram of the circuits. When the "D.F-Sense" Switch is in its upper position the search coil only is coupled with the receiver and the system possesses a figure-of-eight polar curve. To prevent any undesired influence on the receiving circuit due to the loops acting as a plaillj vertical aerial ia shielded transformer is employed, the shield being interposed between the primary and secondary windings and connec, Fig. 7. ed to earth. This method is due t c H. J. Round Commonwealth Letters Patent, No. 15163/20, and prevents any difference of potential occurring due to the capacity to earth of the aerial system. rrhe centrally earthed connection of the field coils also assists in this direciicm. When the switch is in its central position the earthed circuit as well aE the search coil is coupled to the receiver, but owing to the better receiving qualities of the system as a plain vertical aerial, signals from any direction may be received. 'l'hi~ provid_es a ready means for quickly searchmg for a station-the only operation necessary being the tuning of the receiver circuit. The third

position of the switch connects a noninductive resistance in series in the earth connection for correctly phasing and balancing the currents in the loop and earth circuits for '' Heart Shape" reception. The Electromotive Force induced in th0 loops by the impinging wave~ lags 90 degrees behind that induced in the system acting as a vertical aerial, and since inductance predominates in the former circuit, the resultant current lags 90 degrees behind the induced Electromotive :B'orce. If a suitable value of resistance is selectd in the earthed circuit the currents therein can be brought approximately into phase with \the Electromotive Foree in that circuit, and therefore, 180 degrees out of pha,w with those in the loop circuits. This provides th~ phasing conditions for "Heart Bhape" reception, and is very simple and stable in operation. Ji'ig. 6 i,; an illustration of the complete instrument as supplied for Marine use. It is provided with a supersensitive multi-valve receiver employing high and low freuencv amplification. Below the valve amplifier on the left side is the field and search coil or  Radiogoniometer unit whilst in the centre may be seen the Variable Tuning Condenser, and on the right the "D.F.-Stand-biSense'' switch. Fig. 7 is an illustration of the Direction Finder component showing the field coil winding inside of which rotates the search coil To eliminate any errors which might arise from str~y fields affecting the apparatus each unit is provirlecl with- a complete metallic screen. In practice a range of 300 to 400 miles is obtained when working ordinary coast stations and ships, thns ar ample margin is provided over the normal requirements of direction finding. The wave range of the instnunent is 400-1000 metreR. The Land Pattem Direction Finder is somewhat larger than the Marine typt> and differs from it in several respects. The circuit is of the improved type, in which the aperiodic aerial system and tight con p iecl search coil is combined with a foose conplecl transformer. A higher deg-ree of high frequency and low frequeney amplification is also provided. 'i'he system is capable of reception of spark, tonic train, telephony or crmtinuous wave signals.

P.80 - An Expanding Radio Set
An Expanding Radio Set. By C. W. Mann

I HA VE chosen the above name as befitting a set which has been built up from very modest proportions. One sometimes wonders why the average man takes up wireless as a hobby, but no doubt there are many reasons. In my own case profession and taste were the guiding forces, and an inspection of the very fine exhibitioi1 staged by the Metropolitan Radio Club finally decided my action. I chose an Expanse loose coupler and a pair of Brown's 'Phones, and commenced the formidable task of erecting two 35 feei masts from which to drape my aerial. In doing this I gained an experience which may be useful to others, and hence it is passed on. To obviate the swaying 6f the spreaders which, in my own case, was accentuated by the strong winds prevailing at the time, I erected the aerial I attached a light line of picture cord to each end of the spreader and secured it at the base of the mast. On windy days this can be tightened and will effectively prevent all swaying of the 1-,preader and pole. My aerial consists of four wires 150 feet long, and on account of the excellent results obtained I can recommend this size. I commenced with a galena crystal, and nearly all my best results have been obtained by using galena with a "catwhisker," consisting of a single strand of .Jlex soldered to a short length of No. 22 bare copper twisted into a spiral. My experiences in cry:,;tal .work have been very interesting. Out of the many crystals I have collected during geological research work I tested some. thirty or forty, and ad1ieved many interesting results. I found that for good allround work galena was unsurpassed. Molybdenite is a valuable rectifier, giving loud and clear signals when used for short distance reception ; but not of great value for distances over a hundred miles. Bornite alone · and with zincite gave good results, enprite rather poor, while the re:;;ults from magnetile, iron pyrites ancl silieon were very good. It would be interesting to .. secure. a classified tist of resi1lts which have been obtained using a large llllltiber of crystafa, iu{d By C. W. MANN Mr. C. W. Mann, and- I would recommend the classification to some enthusiast. On my crystal set Melbourne and Adelaide time signals are heard with remarkable clearness, and Awanui is frequently picked up. Brisbane is also heard strongly. On one occasiou, while using only the aerial and earth connections with 'phones and detector in series, I heard VIS work-
 * _his Set.

ing VHN (s.s. Katoomba). With the loose coupler VIS has been read at a distance of 27 feet from the 'phones. During the period mentioned Mr. Charles lVIaclurcan (2ClVI) and Burwood Radio (2IX) were the only amateurs regularly transmitting, and they were heard quite plainly at a distance of over six miles, while occasionally we were given a treat by Amalgamated Wireless Ltd. 'rhe experience in tuning gained on a crystal set has been of very great assistance to me, and the expense of the loose coupler has been fully justified . He is a wise dealer who sells us a crystal set when our ambitious selves long to use Armstrong's Super Circuit. My first attempts at valve set construction were probably as humorom; as those of many other amateurs. The loose coupler, good as it was for crystal work, was not a success as the primary and secondary in a valve circuit. One of my experiences is worth repeating. I completed the wiring of the circuit and placed the valve in the socket and stood by. I soon heard 2IX testing and later some music from a phonograph. I then left the set and next morning heard VIS working ships. During the next three weekks I heard nothing. I tightened up the wires, tested every connection, blamed loose coupler, condenser, etc., until nothing remained to adjust or to curse: A new valve solved the trouble. In the old valve the grid and filament touched. I had been blinded to its fault by the fact that signals had once come through normally. The moral is : "Do not al ways blame the wiring or the circuit.'' Test every ·new circuit with at least two separate valves, preferably of different types. After burning out one valve I learnt that it was a fairly safe procedure to i1ivert a voltmeter between the filament prongs of the set before rep] acing the valve. Always · remove tlw valve when you feel inclined to make any alteration in the wiring, aml be careful to iusulafo the high teru,ion leads ,Yith rubber tubing. I soon cli,;carded my first valve set, and designed and built one which I

efficiency. 'l'here is much to be said for the set which rambles over one's desk. The leads are plainly seen and a new circuit can be tried easily. There is usually a tendency, however, to loss of efficiency owing to the capacity effects which are created by the wandering leads. Occasionally one sees a set which fills a small room, but it is questionable if the ability to effect a change of circuit connections quickly nnd easily compensates for loss of efficiency clue to the loose ends. I do not hold that a compact and even portable set combines every aclvantnge, but a glance at the photograph will, I think, reveal at least a few advantages of the compact and portable type; In makil!g my set I kept closely to the old adage: '' Plan your work and work to your plan.'' Get all your material on your bench and then you can have a straight run at the construction. The whole time occupied in making my set-including the cabinet-+-was six hours. The set measures 12" by- 10" by 9", and is monnted on t" ebonite with nickelplated fittings throughout. It is a good plan to use the rule nnd compass freely-the results will amply justify it. To construct such a comparatively small set one. would have to use a Yaricoupler or variometer. My varicoupler is wound with No. 26 D.S.C. on the primary, and No. 30 D.S.C. · on the secondary. Thirteen tappings on the primary control the ihductance and a beautifully smooth-working rotor tickles the primary inductance. 'l'he tuning is very critical and fine, l:nt is easily controlled. On wave lengths from 400 metres to 2,500 metres the capacity effect is not great. The secondary is a periodic and gives good results. In the matter of bu1lding the variocoupler I think a few words would not be out of place. "RADIO" Of course, • the "·inding and assembling is mainly the same "its for any coils. To attach to the panel I first inserted the studs in the panel and attached to each a piece of rubbercovered flax about six or eight inches long. The coupler was then secured in position with a couple of nickelplated screws, and the loose flex drawn tightly, each to its respective tappings and soldered. Do not use killed spirits ; fluxite will do, but a solution of resin in methylated spirits will make a better and more· lasting job. The rheostats and condensers were then attached to the panel and the wiring completed. The constructional details are similar to those encountered in making other valve sets, and offer no difficulties which cannot be solved by the average intelligent amateur as they arise. 'rhe prima.ry coil is 10.3 c.m. in length, allowing 140 turns of No. 26 D.S.C. wire, giving an inductance value of 1,522,582 c.m. 's The primary condenser ( c.i.) has a value of .0012 l\lLF., and this, in conjunction with the inductance, gives a maximum wave length of about 2,500 metres. l have used Radiotron, Myers' And ion QX valves, and others and find that. the results obtained · Page 81 with the Q.X. were far superior to those obtained "·ith anv other valve. All Australian stati01;s have been copied with ease, and I consider it a greater test to copy VIP or VIN on 600 metres than to read NSS or NPM on higher wave length. I would suggest to the amateur who ·wants to find the range of his set that he listens in for the time signals which are always sent by VIM at 12 o'c.a.m., VIA at 12.30 a.m. and VIP at 1 a.m. ( Sydney time). Sydney telephony has been heard even away from the 'phones, but thi8 is a minor consideration. Many amateurs insist that the test of a set is the fact that a concert can be heard at the front gate or down the street, while neglecting the fact that clearness and medium signal strength is the end to be attained il). telephony. l\'.Iy log shows, among otl'ier stations, 2BB, 2CM, 2DK, 2F A, 2IX and 2LA. The set on one occasion had no less than seven head sets attached and signals were loud, in fact, no weakening was noticed at all. I can recommend the circuit and the panel design to any amateurs who want to con-. struct an efficient and compact set. 'l'he panel has a couple of features which make for efficiency. The door is made to drop in front and the panel is set back a couple of inches to allow the door to close when the set is not in use. When open the door makes a good writing desk for copying signals iilto the log. The door at the back is fastened by two dowels and a catch, and can thus be entirely removed to allow one to have a greater freedom of movement when ·working on the set. There are perhaps many details and explanations which I have left unwritten, but I shall be very pleased to assist any amateur in the construction of his set if he will communicate with me, c/o. The Editor of Radio.

P.82 - Wireless Telephone "Call"
'''Wireless Telephone "Call". Transmitter and Receiver.'''

HITHERTO one of the greatest obstacles to a more extended · use of the wireless- telephone has been the necessity for maintaining a continuous watch at the instruments during those periods when communication is expected or desired, means being lacking whereby, as in ordinary telephone practice, a station could be "rung up." This problem has been solved by the introduction of the Marconi Wireless Bell, recently placed on the market by Amalgamated Wireless (Australasia), Ltd. It is an automatic device operated by a distant transmitter, and performs in a simple and efficient manner the same function as that of a call bell on the ordinary land line system. It has been designed so that each instrument is insensitive to all signals except those actually intended to operate it, and, in addition, it enables every wireless set with which it is incorporated to call up as many as five different stations on the same wave length, even in congested areas. Furthermore, an additional adjustment enables still other stations on different wave lengths to be called up, these being selected as quickly and efficiently as the first five. The device is intended for use ir conjunction with any standard type of portable and semi-portable installation, and one of the accompany0 ing illustration shows the apparatus installed in conjunction with a standard set. The principle is to transmit a signal of definite duration on a spe~ cific wavelength, this signal being produced by modulating the outgoing wave at a steady low frequency note. This note is varied by a five point  frequency changing  switch, thus providing the means of calling up any of the first five stations previou,!'lly ref er red to, five being in like manner obtainable on each wavelength within the range of the main transmitter, by means of the  frequency changing switch. It wilI thus be seen that by combinations of wavelength and frequency changes an almost infinite number of calls is available, to intergroup wireless stations. The Call Transmitter is fitted in a teak box, as shown in the photograph, and forms a self contained unit, icomprising a valve :and its oscillatory circuit, with the addition of a fixed resistance to cut down the high tension supply if necessary. The valve circuit produces low frequency oscillations, the frequency being varied by adjusting in five steps the value of the capacity, which is made up of a series of five condensers, each led to a point on the switch. ranged as to start moving when the signal commences, i.e., when the handle is actuated, and to complete its travel, thus cutting the circuit, at the end of the allotted period. The magnet then ceases to be energised and the handle reverts to its original position. The ''Call ' ' Receiver, as will be seen from the photograph, is also a self-contained unit. It consists of two· receiving valves with auxiliary circuits and condensers, for amplification and tuning of the incoming call signal ; a r eaction transformer increases the sensitivity and the signal passes through a galvanometer and two relays to a bell. In practice, the incoming signal · is first received in the usual way by the Main Receiver, the telephone terminals of which ani connected to Portable Wireless Telephone-Telegraph Station, fitted with Marconi Wireless Call Bell. Centre: Instrument Box, Main Transmit.ter and Receiver. Right : Wireless "Call" Receiver. Left: Wireless Call Transmitter. This arrangement is connected to the high tension supply of the oscillating valve of the main transmitter and thus the out-going oscillations are modulated at a frequency determined by the control of the low frequency·valve. · ' · 'rhe call apparatus is set in motion by pulling down· the handle seen on the Ulust,i,ation, thr: handle being held in this position !Jy an electro magnet. The circuit of i,he lattor passes t hrough a, ·dashpot1 s<> &rthe primary of a variably coupled transformer, the secondary forming the grid circuit of the first valve of the Call receiver. This circuit is very accurately tuned by means of the va.riable condenser to the particular note frequency allocated. The plate circuit of this first va:lve is inductively coupled to the grid of the second one and also contains a grid condenser and leak togethel' with the secondary of the reactio11 t ransfol·mer. Note frequenc,r tu,n

ing is accomplished at this stage by another variable condenser. The anode circuit included a small galvanometer and the windings of a G.P.0. Relay, connected to another dashpot. Owing to the presence of the grid leak the second valve normally allows the passage of sufficient current to hold over the tongue of the relay against the "dead" stop. The reception of a signal, however, renders the grid so negative as to reduce the current through the valve. This reduced current is no longer sufficient to hold over the tongue of the relay, which consequently passes to the other stop, thus immediately completing the circuit through the dashpot relay. This dashpot is timed in the same manner as the one which controls the duration of the signal

at the transmitting erid, and once set in motion by the G-.P.O. relay, it completes its travel and operates the bell. It will be seen that only those signals sent by the ''Call' ' transmitter can operate the Call receiver and ring the bell. The telephones are hung on the rest provided on the extreme right of the "Call" receiver, this auto-. rn.atically putting the latter in a. stand-by position ready £or registering a call. To effect the call, the Send-Receiver switch of the main set at the transmitting end is placed in the Send position (i.e., to the left ) whereupon the valve set starts oscillating. The handle of the Call t ransmitter is then pulled down to its full extent and released. From this point onwards the operation is

automatic, as the handle is restored after the required period has expired, this being determined, as explained above, by the transmitter dashpot. At the receiving end, the call bell is set in. motion and continues to ring until the telephones are removed from the rest, whereupon the "Call" receiver will automatically be put out of action and its valves extinguished. The far-reaching :importance of this new development needs little further emphasis, especially in its application to a network of stations. Suffice it to say that by effecting a saving in stand-by charges and
 * materially adding to the convenience

of operation, it leads as a natural sequence to a far more practical and extensive use of wireless telephone services.

P.84 - The Experimenters' Corner
The Experimenters' Corner.

A Storage Battery for the Dry Cell Valve,. THE Marconi D.KR. valve is gaining in popul~rity e".ery day because: of its efficient operation from a single dry cell and low current commmption. The only disadvantage is the cost of the renewals of the dry cell and noises proc1 nced when it approaches exhaustion. This need trouble experimenters no longer, for the problem can easily be overcome by constructing the small storage battery described below. Obtain an old positive and negative plate from a discarded accumulator, and cut a strip from each which includes two complete sections holding the paste in place. A hack saw will do to cut the plate, as the material is fairly soft. Now take a piece qf lead sheet about 4¥n. long and ½ an inch wide, and burn it to the top of the plate. This connection must not he soldered, . because of the su.bsequen t . electrolysis which will taken place when it coni.es in contact with the acid of the electrolyte. This is an easy .iob if tackled as follows: 'l'he material reouired is a small mouth blow-pipe. as 'used for ''dry' ' analysis purposei in chemical work, and a small quantitv of fluxite. Clean the portiom "·here the lug and plate make contact by scraping with a knife, and ,rnrm up. Apply a touch of flux and continue until the lead melts and rum together. A fair amount of skill i~ required to perform this operation successfully; therefore, preliminary experiments should be carried out on some scrap material before tackling the actual job. Stearine from an ordinarv household candle will do for a flux. _. The size of the containing jar depends upon the length of the plates and should be chosen accordingly. "RADIO" An ebonite top should be fitted with the lugs projecting about one and a half inches, and terminals fitted thereto. A small lead pin ahont onerighth inch in diameter should be passed through each lug where it projects . from the cover, to provide a support for the plates underneath For the electrolyte use special battery acid with a specific gravity of 1.200. The capacity of this battery will be in the neighbourhood of 3 amp hours and it can be charged conveniently by using the electrolytic rectifier described in the previous issue of Radio. Regulate the current tc about 0.5 amperes when charging. Loud Speaker Suggestions. No live experim<;inter is satisfied rm til he has been able to so amplify the received signals until they are andible all over the room, and further, if possible. Everyone is not fortunate enough to possess a Magnavox or other type of special loud-speaking apparat.us and so the ordinary head telephoncE are requisitioned for this purpos':). An ·excellent substitute is a receiver from a Baldwin lVIica Diaphragm head set. After a certain stage of amplification has been reached it will be noticed that the receiver begins to rattle a little and distort the music or speech being 1·eceived. The receiver construction iN such that the entire magnet system and diaphragm are supported by an ~tluminium frame work, and are kept clear of the sides and bottom of the case. When the signal energy 1·eache:;c a certain point, the movement set up is so great that the whole of the mag- -May 16, 1923. r+et system and frame work are set into vibration, with the result that the mica diaphragm rattles. To prevent this disagreeable effect taking place, cut several pieces of felt to the same diameter as the inside of the receiver case, and place sufficient inside until the frame-work barely rests upon the edge of the car-;e when it i::.; inserted therein. 'fhis reduces abnorma,l vibration owing to the damping effect of the felt washers, with the result that interference with the weak impulses transmitted to the diaphragm proper is cut. Very often this type of receiver will fail to give its usnal volume of souncl. If this takes place remove it from its case and inspect the small
 * .;pace between the armature and the

permanent magneto. At times a small piece of iron filing or other foreign matter works its way into this spacr and interferes with the freedom of movement of the armature. Cui a piece of paper about a quarter inch wide and several inches long, and work it back and forth along the armature until you are unable to detect anv loose matter which would be likely t~ interfere with the successful operation of the unit. An old gramophone horn should be adapted for this loud speaker, or failing this, the reproducer : on the tone arm of an ordinary cabinet type gramophone ean be removed~temporarily, of course-and the telephone receiver clamped in its place with several rubber bands. In general, if you obtain good clear signals in your detective valve circuit with an ordinary headset, the same quality may be expected from the lond speaker, even with two to three stages of audio frequency amplification.

Meters for the C.W. Transmitter. In the bad old days when spark transmitters were the fashion in experimental circles the only meter, if any, found on the average station. ,vm one of the hot wire type for measuring the aerial radiation current. With the advent of the C. W. Transmitters precise measurements of the voltage and current supplied to the valves is essential if they are to be operated intelligently. The cost of special meters is a considerable item, but if the following suggestion is followed the money f.C. saved can be used for purchasing ad_ ditional tubes or other apparatus. In all motor accessory shops small dashboard meters can be obtained very cheaply. Obtain one of these which will read to about 10 amperes and remove the shunt from the twc terminals at the back. It will now give a full scale_ deflection, with only a small fraction of the original current. 'l'o recalibrate it conriect it up in series with a known resistance and a 6-volt storage battery. The value of the resistance must be such that

the deflection is confined within the limits of the scale. Suppose the meter gives a deflection of eight divisiom when the value of the series' resistance is 150 ohms, this will correspond to a current of 40 milliamperes, and the sensitivity of the meter, therefore is 5 milliamperes per division. Shunts can be fitted to the meter to make it read multiples of this value. For use as a volt meter connect up the battery, and a variable high resistance, as will be described in Mr. -Reed's article in our next issue. Adjust this resistance until the meter reads 6 divisions. lt will no,Y read directly as a voltmeter. For higher values of voltage additional resistance ·will have to be used, in proportion to the increase desired. Eureka wire of No. 36 gaugr sh9uld be used to wind these rrsistances. Its resistance is, approximately, 15 ohms per yard. If possible, calibrate the meter against some reJi::1 ble stimdard. Simple Method of Making Varnished Tubing. Recently an amateur required some varnished tubing, and being unable to secure any at the moment, tried the following experiment: He purchased from a nearby store one dozen soda straws. These he placed i na pan of varnish to soak for three hours, after whcih he was careful to see that the va.rnish d·ried in an even manner. They were then cut to the proper length with a pocket knife. I Page 85 A Vernier Adjustment For Dials. The satisfactory reception of short wave experimental stations requires very accurate tuning\ and it is often found that the adjustment obtained by means of the dials on the tuning elements is too coarse. An excellent vernier adjustment is illustrated below. Obtain a switch assembly from which the contact blade must be removed, and in its place a circular t~·pewriter rubber fitted. Drill a hole 11nder the dial for which the vernier adjustment is required. The exact location of this hole depends upon the size of the rubber, and must be determined by the experimenter himself. When the vernier attachment is fitted to the panel the rubber mnst bear about one eighth of an inch up the bevel of the dial. The spring  C  allows the tension of the eraser on the dial to be adjusted. The pressure must not be heavy or the adjustment wilt be · too stiff. Fit one of these simple devices to your condenser and variometer dials; and get the best out of your set.

P.86 - Technical Terms
'''Technical Terms. Used in Wireless.'''

Aerial.-A system of conductors insulated from and suspended above the ground, designed to radiate or absorb energy in the form of ether waves. Alternating Current.-An electrical current flowing in a conductor, which reverses its direction periodically with time, the  periodic time being the interval between two successive maxima of current in the same direction. A 50-cycle alternating current is therefore one which completely reverses its direction of flow 50 times per second. Ammeter.-An instrument used for measuring the current flowing through a given circuit. An ammeter should always be connected in series in the circuit. Ammeter, Hot Wire.-A meter dependent for its indications upon the change of dimensions of an element which is heated by a current through it. In most cases the expansion of the wire is measured by the alteration in the amount of sag. This type of hot wire ammeter is extensively used in radio transmission work. Ampere.-The standard electrical unit of current, and is that current which flows through the circuit of one Ohm at a pressure of one Volt. Arnplifier.-An · instrument designed for the amplification of radio or audio frequency oscillations. In a; valve amplifier for radio · frequency amplification air core transformers are commonly used as the inter-valve connections, whilst for audio frequeiicy iron· core traiisforiners "are commonly used. Amplifode.-::-The maximum value of current or voltage attained during any half period of an alternating current or voltage is called the amplitude during that half period. Antenna.-See Aerial. ' Atmospherics.-Natural electrical discharges occurring in the ether, which produce disturbances in receiving circuits. They are also known as: X's, strays or  parasitic, signals, and sometimes static.. These discharges are propagated; through the same medium as radio ether waves ~n~ !!!~ t]:wr~fo!(} re~gil;v pi~k(m rip Used 1n Wireless by receivers. At times they are very troublesome, and it is comparatively difficult to tune them out, inasmuch as they have no definite wave length. Audio Frequencies.-Frequencies corresponding to vibrations which are normally audible to the human ear. These are assumed to lie below 10,000 cycles per second. Broadcasting.-The radiation of ether waves in all directions used for the purpose of conveying intelligence either by radio telegraphy or telephony from a given central point for the benefit of a large number of receiving stations located within range. Capacity.-That property of a material system by virtue of which it is capable of storing energy in electro- static form. Capacity is measured by ratio of the quantity of electricity stored to the potential difference at which it is stored. Capacity, as well as Inductance, is a factor which determines the time period and wavelength of a circuit. The unit of capacity is the Farad, but this is too large for practical purposes, thus a sub-unit, the Micro-farad, is used, which is one millionth part of a Farad. · Cascade Arnplification.-A method of amplification of radio signals employing several valves joined in cascade or series. Choke Coil.-A coil possessing great self-induction, which introduces a choking action in an alternating current circuit. Circuit.-A path in which an elec" tric current flows .from the source and - returns to it; A circuit may be either .open, closed or,, oscillating. Coupling.- The action between two circuits enabling energy to be transferred from one to the other. The connection may be by magnetic linkage, electro-static linkage; direct connection, or any combination of these. Condenser.-A material system possessing electro-static capacity. Two conducting surfaces separated by a dielectri'e'. C 'Condensers are used in radio work · for · storing · electrical energy, and for bringing circuits into a_ condition, of :resonan(le or tuning them, · _, Counterpoise.-A system of electrical conductors forming one portion of a radiating oscillator, the other portion of which is the aerial. It consists of one or more wires suspended on insulators immediately above the earth and usually directly beneath the aerial. Continuous W aves.-The term applied to undamped waves radiated from an aerial system in which oscillations are sustained. The continuous waves make possible signalling over longer distances than can be covered by the older form of discontinuous or highly damped waves. Crystal Detector.-A detector which uses the rectifying properties of the contact between a crystal and a metal surface or between two crystals. . De,tector.-A device which translates the high frequency energy into an intermittent direct current suitable for operation of a telephone receiver or indicator. Direct Ciirrent.-An electric current flowing continuously in one direction. Direct current always flows from the positive source to the negative return in a two-wire circuit, and therefore has a readily determinable · polarity. Alternatiii.g current which is periodically r eversing its polarity while flowing through a circuit has no apparent polarity. Earth.-The connection to the earth which in most systems forms the lower extremity of the aerial system. It usually consists of a system of metal plates or wires or combination of both metallically connected together and more or less deeply buried in the ground. Electron,_:_The natural unit of negative electricity. An atom combined with an electron is a negative ion, whilst an atom minus an electron is a positive ion. Electro-Motive Force.-The force which tends to displace electricity, and is equal to the difference of potential between the points considered. The · unit of Electro-Motive Force is th Volt.

(To be Oontin'Ued.)

P.87 - Condenser as Waiting Room for Electrons
Condenser as Waiting Room for Electrons.

We all know what a condenser is -two sets of metal plates insulated from one another. But what is it in terms of electrons-those tiny specks of negative electricity which are so useful in vacuum tubes f The answer to this question is given in the foll + t B '-11J1j1---_, FIG-1 lowing article prepared by John Mills, former professor, author an_d engineer of the Western Electric Company. . A condenser is merely a gap in an otherwise conducting circuit. It is a gap across which electrons cannot pass so that if there is electro-motive force in the circuit electrons will be very plentiful on one side of the gap and scarce on the other side. If there are too many: electrons waiting beside the gap there must be room for them. For tha.t reason we usually provide waiting rooms for the electrons on each side of the gap. Metal plates or sheets of foil serve nicely for this purpose. For Service Telephone : 1180'·City The RAPID FREIGHT DESPATCH CO. CUSTOMS. SHIPPING & FORWARDING AGENTS Broughton House, King Street SYDNEY ........ . .... "RADIO" Waiting Room Look at Figure 1. You see a battery and a circuit which would be conducting except for the gap at C. On each side of the gap there is a sheet of metal. The metal sheets may be separated by air or mica, or paraffined paper. The combination of gap, plates and whatever is between, provided it is not conducting, is called a condenser. WHEN WE CONNECT A BATTERY. Let us see what happens when we connect a battery to a condenser, as in the figure. The positive terminal of the battery calls electrons from one plate of the condenser, while the negative battery terminal drives electrons away from itself toward the other plate of the condenser. One C + ! R plate of the condenser, therefore, becomes positive, while the other plate bei::omes negative. Page 87 for Electrons This action of the battery will go on until there are so many electrons in the negative plate of the condense_r th~,t they prevent the battery from adding any more electrons to that C + L FIG-3 plate. The positive plate of the battery calls electrons away from the condenser plate, which is making positive, until so many electrons have left the protons that the atoms of the plate are calling for the electrons to stay home just as loudly and effectively as the positive battery-terminal is calling them away. When both these conditions are reached-and they are both reached at the same time-then the battery has to stop driving electrons around the circuit. The battery has not enough electromotive force to drive any more electrons. Why f Because the condenser has now just enough electromotive force with which to oppose the battery.

WHAT IS THE CHARGING CURRENT? We say that the battery sends a "charging current" around its circuit and. '' charges the condenser': until it has the same electromotive force. When the battery is first connected to the condenser there is lot,: of space in the waiting rooms, so there is a great rush or surge. of electrons into one plate and away from the other. Jnst at this instant the charging current is large, but it decreases rapidly, for the moment the electrons start to pile up on one plate of the condenser and to leave the other, an electromotive force builds up on the condenser. This electromotive force of course, opposes that of the battery. so that the net electromotive force acting- to move electrons round the circuit is no longer that of the battery, but is the difference between the

electromotive force of the battery and that of the condenser. WHY THE CURRENT STOPS. And so, with each added electron, the electromotive force of the condenser increases until fiiially it is just equal to that of the battery, and there is no net electromotive force to act. What would happen if we should then disconnect the battery? The condenser wo11ld be left with its extra electrons in the · negative plate and with its positive plate lacking the same number of electrons. That is the condenser would be left charged and its electromotive force ,Yould be of the same number of volts as the battery. THE ELECTRONS RUSH HOME. Now suppose we connect a short wire between the platrs of the condenser, as in Figure 2. The electrons rush home from the negative to the positive ph1te. As fast as they get

home the electromotive force decreases. When they are all back the electromotive force has been reduced to zero. Sometimes we say that " the condenser discharges. The  discharge current'' starts with a rush the moment the connecting path is offered between the two plates. The electromotive force of the condenser falls the discharge current grows smaller and in a very short time the condenser is completely discharged. That .'s what happens when there is a short conducting path for the discharge current. If that were all that could happen I doubt if there, would be any radio communication to-day. but if we connect a coil of wire between two plates of a charged condenser, as in Figure 3, then something of great interest happens. Tc understand you must know something more about electron streams in coils.

Erecting an Aerial
Rccc-ivi11g P!trposrs Only.-One wire of sufficient length, say, 100ft. or over, according to wave length to be received, of 3/ 20 copper is all that is needed for reception. Height.-The higher the wire is suspended from earth and surrounding objects the better it ·will function. lnsitlation.-This should be carefully attended to, as if any leakage to earth or objects connected to earth occur, naturally a considerable amount of the signal current shall leak down these instead of passing through the instruments to earth as desired.

P01:nts of Suspension of A erial.These points may be either of the following : Masts, buildings, trees, chimney stacks, or any other isolated structure. Where trees and buildings are used the aerial must be swung clear of these by at least ten feet. Masts.-These may be of steel, iron, galvanized iron piping. The general type of amateur mast is a sectional wooden t?pe. Mast Erection OF ood ) .- It is advisable to have the first section o

fairly heavy timber, say 6" by 6" and of oregon, the second section 4" by 4" and the third 3" by 3". The length of each section should be about 30 feet. Each lap being 6 feet and the ground pole 3 feet in the ground, this would make a height of 27, 24, 24 = 75 feet. Each lap should have two iron bands shaped so as to accommodate the two different sizes of the poles ; these bands should be split so as to take up any slack in the band by tightening up nuts. Band should be 3" wide and r thick, with a lug on each face for the fonr stay wires.

P.89 - Wireless Aid to Injured
'''Radio's Proud. Record. Robbing the Sea of Its Terrors. Summit of Splendid Service.'''

P.90 - Call Letters
Call Letters.

This is the fourth list of call letters of Australian and New Zealand ship and land stations. In subsequent issues of "Radio" further lists will appear, all of which should be preserved so that readers will have a complete list of both local and overseas stations.— Ed.

 * VXR s.s. Moorabool
 * VXS s.s. Yarra
 * VXT s.s. Delungra
 * VXU s.s. Dinoga
 * VXV s.s. Ditmosa
 * VXW s.s. Dundula
 * VXX s.s. Mackarra
 * VXY s.s. Macumba
 * VZA s.s. Camira
 * VZB s,s. Makambo
 * VZBC s.s. Komura
 * VZBD s.s. Koonda
 * VZBF s.s. Melboitrne
 * VZBJ s.s. Hexham
 * VZ B K s.s. Gabo
 * VZ B L s.s. Poolta
 * VZ B M s.s. Era
 * VZ B N s.s. Omana
 * VZ B P s.s. Coolcvna
 * VZ B Q s.s. W arspray
 * VZ B R s.s. Moreton Ba.y
 * VZ B S s.s. Largs Bay
 * VZB 'r S.S. Koolonga
 * VZBU s.s. Maindy Lodge
 * VZBW s.s. Hobsons Bay
 * VZC s.s. Cantara
 * VZD s.s. Dilkera
 * VZE King Island Radio
 * VZF s.s. Junee
 * VZG s.s. Governor Mitsgrave
 * VZH s.s. Karuah
 * VZI s.s. Kadina
 * VZJ s.s. Lammeroo
 * VZK Morobe Radio
 * VZL s.s. N ardoo
 * VZM s.s. Carina
 * VZN s.s. Tarcoola
 * VZO Manus Radio
 * VZP s.s. Australpool
 * VZQ s.s. A nstralcrag
 * VZR Kaeweing Radio
 * VZS s.s. Australpeak
 * VZT s.s. A ustralport
 * VZu S.S. u rilla
 * VZV S.S. Calulu
 * VZW s.s. Australmead
 * VZX Eitape Radio
 * VZY s.s. Australmount
 * VZZ s.s. Marrawah
 * WGEA s.s. Easterner
 * WHL s.s. Ventura
 * WHM s.s. Sonoma
 * WIS s.s. E.R. Sterling
 * XHO s.s. Port Nicholson
 * XHP s.s. Port Bowen
 * s.s. Port Caroline
 * s.s. Clan Macmillan
 * s.s. Canadian Volunteer
 * s.s. Canadian Trooper
 * s.s. Canadian Trader
 * s.s. Canadian Sai.lor
 * s.s. Canadian Seigneitr
 * s.s. Canadian Signaller
 * s.s. Canadian Miller
 * s.s. Canadian Adventi1.rer
 * s.s. Canadian Gunner
 * s.s. Canadian Am:ator
 * s.s. Canadian Sower
 * s.s. Canad-ian Settler
 * s.s. Canadian Navigator
 * s.s. Canadian Sealer
 * s.s. Canadian Spinner
 * s.s. Can.adian Raider
 * s.s. Canadian Ranchm·
 * s.s. Canadian Planter
 * s.s. Canadian Importer
 * s.s. Canctdian Exporter
 * s.s. Canadian Inventor
 * s.s. Canadian Prospector
 * s.s. Canadian Miner
 * s.s. Canadian Farmer
 * s.s. Canadian Beaver
 * s.s. Port Darwin
 * s.s. Port Denison
 * s.s. Clan Maclaren
 * s.s. Clan Macanlay
 * s.s. Clmi Mackay
 * s.s. Eastern
 * s.s. W aimarino
 * s.s. Hatarana
 * s.s. B errima
 * ZBL s.s. Northumberland
 * ZLT s.s. Port Elliot
 * ZLU s.s. Port Sydney
 * ZNZ s.s. Port Napier
 * ZPD s.s. Port Lyttleton
 * ZSU s.s. Port Stephens
 * ZSV s.s. Port Pirie
 * ZSW s.s. Port Melbourne

P.91 - Movements of Wireless Officers
Movements of Wireless Officers.

Mr. F. C. Davies who was' relieved on s.s. Mataram by Mr. A. H. Jeremy, relieved Mr. C. F. Griffiths as senior operator of s.s. Changsha at Sydney on April 27. Messrs. 0. S. Kelly and A. C. Jackson joined s.s. Changsha as 2nd and 3rd operators respectively at Sydney on April 27. Mr. E. M. Stearson signed off s.s. Montoro at Sydney on April 26. Mr. L. G. Graham signed off s.s. Waimarino at Newcastle on April 25. Mr. :B'. A. Noar signed off s.s-. Waikawa at Newcastle on April 25. Mr. N. W. Leeder who was relieved by Mr. A. G. Ross on s.s. Zealandia at Fremantle on April 27, is standing by to join s.s. Gascoyne. . Mr W. G. McEwan signed on s.s. Age, at Sunderland, on February 9. Mr. G. Hugman relieved Mr. F. S. Stevens on s.s. Bombala at Sydney on April 24. Mr. T. Laidlaw signed off s.s. .1:iitstralmead at Sydney on April 24. Mr. M. L. Robertson signed off s.s. Gorgon at Fremantle on April 23, and proceeded on H.P. leave. Mr. K. J. Dines signed off s.s. Moorabool at Geelong on April 21, and returned to Sydney. Mr. J. H. Bennett transferred £rom s.s. Maori to s.s. Mararoa at Lyttleton on April 13. Mr. J. A. Guy, who was on s.s. Iron Prince when that vessel :was wrecked, has now returner! to Sydney. Mr. A. C. HickPy signc>d off s.s. Australplain at Me1bourne on Jlpril 14, and proceeded on H .P. leave on April 26. Mr. W. H. G11orge signed off s s. .1ustralpool at M<:lbourne on .April 21 and proceeded on H.P. kave five days later. Mr. C. J. Lilley signed on s.s_. Di?ga at Melbourne on April 27. - Mes.srs. J. E. Elmore and W. D. Wedgwood (senior and 3rd operators respectively) signed off s.s. Parattah at Sydney on April 30, and proceeded on H.P. leave. Mr. H. W ormwell relieved Mr R. J. Webb on s.s. Period at Melbourne on April 13. Mr. E. I. Hyde transferred from s.s. Carina to s.s. Alabama at MelLonrne on April 27. Mr. H. K. Wadsworth transferred from s.s. Alabama to s.s. Carina at l\folhourne on April 26. Mr. C. F. Griffiths relieved Mr. A. Cuthill as senior operator on s.s. Montoro, at Sydney, on May 2. Mr. Cuthill is now on H.P. leave. · Messrs. D. Soraghen and M. C. Wedgwood joined s.s. Montoro as second and third operators, respectively" at $ydney, on May 2. MeRsrs. W. C. Smith and E. C. Bouel (second and third optITators) signed off s:s. Arafura on May 2, and Mr. Smith is now on H.P. leave. Mr. F. L. Scott signed off s.s. Araimac at Brisbane on April 27, and proceeded on H.P. leave. Mr. M. G. Crockett transferred from s.s. Eriba to s.s. Ellaroo, at Melbourne, on May 1.

High Speed Wireless

 * B'urther wireless facilities for

passengers travelling between Europe and America on the giant White Star liner Majestic have just been provided. A short time ago the Majestic _was fitted with high speed transmitting ' apparatus, and high speed automatic receiving apparatus has now been added in order to facilitate the handling of the ever increasing number of wireless messages dealt with by this vessel. Not only is the Majestic the largest ship afloat but she is also a favourite with business men. Her wireless traffic exceeds that of any other ship and specia.l facilities are required to deal with telegrams expeditiously. The high speed transmitting apparatus has proved of great value in despatching the. l1trge number of messages which are' sent when ap-· proaching the United States; and the fi~ting of a~tomatic- receiving gear will be of still further advantage in enabling the ship to maintain its high reputation for the expeditious hand- , ling· of telegrams.

P.92 - Weather Reports by Radio
'''Radio's Proud. Record. Robbing the Sea of Its Terrors. Summit of Splendid Service.'''

P.93 - Radiofun
'''Radio's Proud. Record. Robbing the Sea of Its Terrors. Summit of Splendid Service.'''

P.94 - Club Notes & News
Club Notes & News.

WIRELESS INSTITUTE OF AUSTRALIA N.S.W. DIVISION. T HE newly-elected Council of the above Division held its first meeting at the Wentworth Hotel on April 25, those present including Messrs. F. Basil Cooke, VicePresident ( in the Chair), Crocker Renshaw, Maclurcan, Gregory, and Mingay. 'l'he first business transacted was the election of a President for the e1isuing year, and Mr. C. l\!Iaclurcan was unanimously chosen. Messrs. F. Basil Cooke and Crocker were elected Vice-Presidents, Mr. P. Renshaw Hon. Secretary, and Mr. 0. F. Mingay Hon. Treasurer. By reason of the fact that Messrs. Renshaw and Mingay were then ex-officio members of the Council their resignation as Councillors was accepted; and Major Newman and Mr. S. Colville were elected to the vacancies. A full Council was thus constituted. The Committee appointed to organise the Wireless and Electrical Exhibition in the Sydney Town Hall reported that it had been decided to postpone the exhibition for a few weeks in order to allow of a more successful result being achieved. 'l'here is no intention whatever of abandoning the display, and all concerned mav rest assured that it will be held in· the near future. A discussion regarding the appointment of Honorary Radio Inspectors resulted in Mr. l\!Iaclurcan being nominated on behalf of the Institute to act as  transmitter station examiner. "RADIO" QUEENSLAND DIVISION. 'l'he annual general meeting of the above Division was held in the lee: ture room of the old Fire Brigade building about the middle of April. '!.'here was an excellent attendance of members, and keen interest was manifested, in the proceedings. The Annual Report and Treasurer·~ statement were read and adopted. The following officers were elected for the ensuing year :-Patron, Professor Hawken; Vice-Patron, Professor Parnell; Honorary Membern, Messrs. J. M' Conachie (Deputy Postmaster- General), J. W. Sutton ( State Engineer), F. W. Walker (Deputy State Engineer), S. V. Colville founder of the Queensland Division) ; President, Mr. A. G. ,Jackson; VicePresidents, Messrs. C. W. Isles, A. K. Lawton, P. S. Trackson, S. H. Sm;th; Hon. Secretary, Mr. W. J:<'inney; Hon. 'I'reasurer, Mr. A. N. Stephm1s; Hon. Auditor. Mr. H. Maddick · Broadcasting Committee, Messrs. E'. C. Littler, J. Milner, A. N. Stephens; Committee, Messrs. A. M'Leod, J. Milner, J. C. Price, and E. C. Littler. BRIGHTON AND DISTRICT RADIO CLUB. The first meeting of the Brighton and District Radio Club was held at 18 Willansby Avenue, North Brighton (Vic.) on Thursday, April 19. T~e attendance, though fair, was not qmte up to expectations, but it is expected that the membership will be increased when the club's existence becomes more generally known. 'I'he following office-bearrn, werr elected: President, Mr. T. H. Crago· Hon. Secretary, Mr. W. Kerr; Hon'. Treasurer, Mr. P. Thompson. It was decided as a temporary arrangement. and until other club-room provision "' ·i I May 16, 19~3. can be made, to hold meetings at dif ferent members' homes every altn" nate Thursday. All communications and enquiries concerning the club should be addressed to the Hon. Sec., W. Kerr, 28 Durrant Street, Brighton (Vic.). MANLY AND DISTRICT RADIO CLUB. An instructive lecture on "Valves'' was delivered by Mr. Best, of the Wentworth Radio Club, at a recent meeting of the above Club. Mr. Best attended at very short notice but despite this his lecture was most interesting and helpful to those anxious to gain a knowledge of the working of valves. 'l'he cordial appreciation which was exprrssed a1 the conclusion of the lecturr must have convinced Mr. Best that the members of the Manly Club were not slow to recognise his excellent effort. Amongst the general business transacted was a decision to affiliate with the Radio Association of New South Wales. Mr. Symes, the Club Secretary, was appointed delegate. It _was also decided to support the appomtment of four honorary inspectors. A working bee is to be organised in the near future to carry out the task of erecting the aerial poles. '~he Club has received generous asR1stance from the Committee of the ~iterary Institute, many of whom are mtensely interested in radio telephony. At the usual fortnightly meeting held on Monday, May 7, R. C. Marsdrn, of the Wentworth Radio Club, attended and delivered a lecture on the relative merits of crystals and valves. Mr. Marsden displayed a thorol:gh knowledge of his subject, and his lecture was most instructive

P.95 - Long Wave Stations
Long Wave Stations.

Those experimenters who have facilities for tuning to long wave stations will no doubt find the following list useful the first column showing the wave length, the second call letters, the third the name of the station, and the fourth column the method of transmission. vVave L ength. 2,000 2,300 2,300 2,300 2,500 3,375 3,375 4,800 5,000 5,000 8,800 9,400 9,800 11,200 12,600 14,200 15,200 17,750 17,000 18,000 23,400 Call. VLA PKC PKD PKE PKX PKF PKG NPG JJC NPO PKX POZ NPL NPM POZ MUU y N. .. PCG NSS PKX Ly .. ......, Name of Station. Awanui (N.Z.) ..... . .... . Sitoebondo .. , ..... . ... .. . Koepang ........ . .. ... .. . Amboina .... . ...., ... ... Malabang. ... . .. . . .. ., .. . Balikpapan. . .... .. ... . .. . T a rakan ....... . .. .. .... . San Francisco .. . . ...... . Funabashi (Japan) Cavite (Ma nila) .... . .. . . . Malabang .. ... . ......... . N auen (Germany) San Diego. . .. . .. . ...... . Pearl Harbour (Honolulu) Na u en ........ .... ..... . Carnarvon (Wales) .. .. . . . L yons (F rance) .. . ... .. . . K ootwijk-Sambeek (D.I.E.) Anna polis (U.S.A,) Malabang (D.E. Indies) .. Bordeaux (France), , ,. , . . Method of Transmission. Spark Spark Spark Spark Continuous Wave Spark Spa rk Continuous Wave Spark Continuous Wave Continuous Wave Continuous Wave Continuous Wave Continuous Wave Continuous Wave Continuous Wave Continuous Wave Continuous Wave Continuous WavP Continuous W ave Contin\l0us Wave

P.96 - Queries Answered
Queries Answered.

Answer: (1) 'l'he formula for the · capacity of a condenser expressed in centimetres (C.G.S. units of capac( n-1) AxK ity) is Oms =--where 11 = 4rrD number of plates. A=Area of one side of one plate i11 8ll, ems. K=Specific inductive capacity of the dielectric ( Air = 1), and D = Thickness of dielectric in centimetres. (NOTE.-One micro farad equals 900,000 ems.) The capacity of two plates 3in. x 2in., separated by a sheet of wax paper (S.I.C. = 2) 5 mils thick would be calculated as follows: 3 x2 X (2.54) 2 X 2 C = -= 490 ems, 4 ,r 0.005 X 2.54 or 0.00054 miero farads. ( 2) You will be unable to cover so great a range with one set of coils. For work between 350 and 2,000 metres wind the primary with 100 · turns, 22D.C.C. tapped every 10 turns, .. and the secondary with one winding of 120 turns of No. 30 D.S.C. Shunt condensers of 0.001 microfarads will be required for both circuits. N. A. F. (Mt. Mulligan) asks (1) What license is required for a receiver "RADIO" to tune between 400 and 600 met.res. (2) Will 220 Volt D.C. overhead power mains, which run both parallel and at right angles to aerial interfere with reception. (3) Would it be possible to utilise these mains for the filament and plate currents of a V 24 valve. ( 4) Will the aerial ( as per sketch enclosed by him) be suitable. ( 5) Would a regenerative circuit be most efficient, and sketch of same, giving particulars of A.'l'.I., etc. (6) If ( 3) be possible would not the waves radiated, by the overhead mains be neutralised by the valve being connected to same circuit. Answer: (1) Application for an experimental license should be made to the Controller of Wireless, Melbourne. (2) Slight induction may be experienced. (3) Yes, but the apparatus required to break down the voltage and current and smooth out the commutator ripple would probably cost more than the high and low tension batteries. 4. The aerial is satisfactory for waves above about 400 metres. ( 5) Yes. The circuit employed by Mr. Slade, and described in No. 1 issue would be most suitable for you. A primary winding of 50 turns on a 4 inch tube, with taps every 10 turns, and a re-action coil of 50 turns on a 3 inch tube would tune in both 40C and 600 metre sigs with your aerial. ( 6) Connection to the mains would be more likely to increase than decrease the induction. N.W. (Goulburn) asks for detailE May 16, 1923. ,t(QJ) ~ ,@) 11 of high frequency transformers of the plug-in-type suitable for 200-450 metre waves. · Answer: An article by Mr. Reecl. in this issue provides the information you reqmre. A.L.C. (Leeton) asks (1) Would one valve be sufficient to receive in Leeton music broadcasted from Syd. uey? (2) Would a loose coupler be as efficient if insteacl. of using a slider on the primary, taps were taken every ten turns and a variable condenser used in paralld with t.he indnctanee ( 3) W oul,d a crystal detector and an amplifying valve be imitable for the reception iu Leeton of music from Sydney? Answer: (1) If you have an efficient aerial system reception of music from experimental stations is possible with one valve. (2) Greater efficiency will be obtained by the use of a tapped inductance and tuning condenser. (3) We would recommend you to use your valve and crystal in the special reflex circuit described elsewhere in this issue. Galena: ( Glen Innes) asks How much No. 40 enamelled wire woulc be required to rewind an orcl.inar telephone receiver, and what woul be the resistance, using proper diaphragm? Answer: You should use No. 44! S.W.G. Beldenamel wire for this purpose. One ounce will suffice for a 2000 ohm winding. Only about 200 ohms per receiver will be obtained with No. 40 wire.