text:
History of wireless telegraphy and broadcasting in Australia/Topical/Publications/Radio in ANZ/Issues/1923 05 30

Link to Issue PDF
WorldRadioHistory.com's scan of Radio in Australia and New Zealand - Vol. I No. 05 - 30 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 30

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 30, 1923 — No. 5

(Start Graphic Description) The smile of a deaf man who hears for the first time through radio receivers.— "Wide World" Photo (End Graphic Description)

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

P.97 - 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 30, 1923    Number 5

P.97 - Contents
CONTENTS.

 * Radiotorial . . . Page 99
 * How Sydney Radio Works . . . Page 100
 * Radio and Reflex . . . Page 105
 * Commonwealth Controller of Wireless . . . Page 109
 * The Experimenters' Corner . . . Page 110
 * Patents Section . . . Page 112
 * Mr. J. H. A. Pike's Station . . . Page 113
 * West Australian Work . . . Page 115
 * Club Notes and News . . . Page 116
 * "Iron Prince" Incident . . . Page 118
 * Queries Answered . . . Page 119

P.97 - 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.98 - View of Sydney Radio Station at Pennant Hills
(Start Photo Caption) View of Sydney Radio Station at Pennant Hills, showing mast and buildings. The station grounds cover 40 acres. (See Special Article on page 100.) (End Photo Caption)

P.99 - Radiotorial
Australian Experimenters Succeed.

I'l' SPEAKS vo.lumes fort.hes.kill and enthusiasm of ing to establish an hitherto unattempted record. Accept- Australian experimenters, and the efficiency of their ing that as the position, the trans-Pacific test had to be stations, that wireless signals sent from America conducted under a veil of secrecy which, while regreton low-power have been received in Australia during table, was necessary. the past few weeks. _ _ - It is, however, gratifying to know that success was 'fhat one or another experimenter received the sig- achieved, and there can be no question that in this innals first may be a matter of individual moment, but stance, at least, the end justified the means. from a national viewpoint it is not nearly so import- It is probable that a few years hence the receipt of ant as the fact that the signals have been received, and low-power signals over a distance of 7,000 miles will he by an Australian. c1uite an ·ordinary event. That, however, ,vill not rob the 'l'o prevent interference from experimenters _ who _____ recent performance of any of its merit. On the contrary. were not actually taking part in the test it was neces- it will enhance it. History teaches that no matter what sary to preserve secrecy regarding the arrangements. advances may be made in any particular science or in- This probably explains the fact that outside of a limited dustry, the pioneers who 'laid the foundation stone upon 11umber no mention was made that a private test had which later successes were built are the men wb.ose been arranged between a well-known Australian experi- achievements never die. menter, and one of similar standing in America. Jt says much for the whole-hearted enthusiasm witl: This private test commenced almost simultaneously which experimenters iu Australia have applied themwith the more widely advertised one, and was responsible selves to the task of receiving low-power signals fro1i, for the first signal being recorded in Australia. It is a their fellow-amateurs in America :that such marked suclllatter for regret that the need for secrecy prevented cess has been achieved at so early a-stage in the attempt. the public being· more fully acquainted with the nature 'l'here need be no fear regarding t he future of radio i11 and importance of these long-distance low-power tests. Australia when such excellent performances can be 'l'o have advertised them widely would have defeated the pointed to. vVe have all the materia1 here upon which very object for which the test was held. It is apparently to work, and he would be a pessimjst, indeed, who would asking too much of human nature to expect the hundreds hold any doubts regarding· the a.bility of those interested of experimenters throughout the various States to sns- in radio, whether technically or commercially, to pend part of their acti,ities over a, limited period during make the most of the opportunities which the future 1111- ll'hich a number of men, more highly qualified, are seek- 11uestionably holds. -- ---

Radio Association of N.S.W.

A COMMENDABLE spirit of. enterprise has been shown by the various radio bodies in New South Wales in forming an association to assist the .\Iinister in charge of Wireless in administering the Act to the best interests of an· concerned. The point has frequently been stressed that if radio is to reach the peak of its possibilities in Australia there must be the closest co-operation between all who are anxious to sec that point reached. Iu other undertakings we are all to? frequently treated to the spectacle of associations bemg formed which hinder rather than help the future of an enterprise in which they arc directly concerned. It may_not be that they deliberately set out to work harm, but lll the course of destructive criticism harm is nevertheless wrought. · _ - It can be confidently assumed that the Minister will eet the association in the same spirit as it approaches lln. Harmony should thus prevail, ,ind the ,vay be - .- •. paved for the ac_compJishment of much useful work. It is no ,libel on the great body of experimenters in Australia to say that: there is a limited number who will always cause sufficient annoyance to provide scope for the activities of the Radio Association. It would be surprising if it_ were otherwise. Human nature is impulsive and the desire to do things without giving a thought to the possible interference we are causing others frequently leads to transgressions, which, at heart, the offender has no wish or intention to commit Hence the need for supervision, such as the Radio Asso - ciation will exercise. In addition to this it will safeguard the legitimate interests of radio experimenters, and so pave the way for smooth and satisfactory working. The immediate and lasting effect of this will be to promote goodwill amongst all concerned, and, incidentally lay a solid foundation for the futnrr) of radio i11 Australia.

P.100 - How Sydney Radio Works
'''How Sydney Radio Works. A Peep Behind the Scenes. Up-to-Date Station — Efficient Staff.'''

FEW people in Australi~ _a_nd N~w a th_o_roug'hfare :rell patronised _by Zealand are unfamiliar with c: motorists. ' · 'l'he · huge steel lattice the name of Sydnejr 'Radio.· · mast, · which towers' to · a height of Oversea and inter-State ocean travel-· - 400 feet, is -a. conspicuous landmark lers know it well. - 'l'o them it repre- - for miles around. Standing in silent sents one of the links in the chain of : and im1)ressive majesty, it dwarfs to comrnunieation al,rng which flash the · insig1iifieai1ce the b'uildings which m~ssages of gre0ti11g or farewell, busi-,, stm1d adjacrnt, and whrn we viewed ness communications, ai1d in time of - it at· close · range for the first trouble the call for help. 'ro the lay- -time we instinctively prepared for man it has always been known as the further eye-opening facts and Pennant- Hill1;, Wireless Station, and- Rights which ,rnre to follow. as - sirnh it will · probably · remain. The name does not matter greatly, after all, for nothing can rob the s ta t i o n of the credit which justly attaches to it for the consistently splendid service it rrnders t o t h e
 * -;hipping and commercial

interests of the State. STAFF OF SYDNEY RADIO. closely related to the ill-fated" human fly'' of America to do so) the intrepid climber might well say: "Not only am I half way to heaven, but -I have the world at my feet.' ' 'l'he main mast, or tower, is not fastened in any way at the bottom, but rests on large glass insulators of a special quality and design. 'l'his is hard to realise until it is actually seen, particularly when it is remembered that the mast weighs about 50 tons. Heavy iron guys, which are made fast to s t e e 1 girders in concrete " anchorages serve as stays for the mast. These girders do not bear directly against the concrete, but pull against flat g 1 as s insulators similar in pattem to, but smaller than those under'!' hose who have neath the mast. had actual experience of the work clone by Sydney R a d i o need nothing further to convince them of the valuable part it is playing in onr everyday life. Others know of it only through readin the daily pa- Front Row (left to righ~-): J. -G. ,~ooks~n (Mechanic), G. F. Chilton (Oif(cer1ri· Charge)°t'J, D; '" Reyn'olds, Acting First Operator; From the extreme top of the tower is suspended the aerial system for high-p owe r t r a n s m i s s i o 11. 'l'here are six legs in this ae ri a l, which is of the " squirrel c age" type, similar to Back Row (left to right): W. C. H. Hodges, P. W. Brown, J. R. Clifford, and C. F. Dale, Messrs. G. H. Brown (Senior Mechanic) and C. E. Lemmon (Chief Operator) were on Leave of Absence at the time pers, which from time to time feature incidents of outstanding importance in which Sydney Radio figures, but the time has arrived when the "inside" story of the Station and its work must be given to the wide, wide world. 'l'he Radio Station is situated at Carlingforcl, about 17 miles from Sydney, and stands in grounds covering an area of about 40 acres. One side faces the Pennant Hills road:_ the Photo was taken., A ladder is built inside the mast, and runs to the top, where a small platform is erected. If one has the energy and nerve to climb that ladder to its very peak a wonderful sight is unfolded. On a clear -day Sydney Heads. stand out quite distinctly, and no matter in which direction one gazes a splendid view is presented. If it were possible to feel sufficiently at home at such a giddy height (it "'ould be necessary to be those seen on battleships. 'l'he legs of the aerial -three on each side-are supported by steel rope halyards from small ladder masts in the four corners of the station grounds. 'l'he feeders for the aerial are also of the  squirrel cage  type, and run almost vertically from a position outside of the operating buildings to the top of the mast. 'l'he whole system resembles a huge umbrella, and it has a very neat and symmetrical appearance, owing

to the spreader discs inserted every few feet to keep the wires evenly spaced and taut throughout their leiwth. During last Augrn,t this aerial was used for the transmission of pre:,;s messages to ships at sea, and the Niagara, en route to Vancouver, received the messages from this station each clay until two days north of Jio±iolulu, when transmission ceased. ,Just above the first section of the lllast at a height of about 150 feet from the ground is suspended the '' T · ·-shaped aerial \vhich is iised for emnmunication with ships at sea on ,rnve lengths of 450 and 600 metres. In comparison with the larger system this aerial appears very small, and, indeed, it is relatively so compared with some used elsewhere for the same purpose. Nevertheless, it is very efficient, and communication has been established at various times, when using this aerial at distances over 4000 miles. Sydney Radio is probably the lrn,:;iest station in the Southern Hemisphere used for communicating with ships at sea. A similar station is erected at Applecross, W.A., a small settlement on the banks of the Swan High Tension Room V I S. In the foreground are six banks of sixteen "quenched" gaps in each. In the ba ckground the Leyden Jar Condensers (12,000 ems each), with provision for using a number of series-parallel groups, according to power used. To the right the 35 K.W. transformer, and behind it the 5 K.W. transformer, with switch (controlled from operating room), for changing from low-power to buzzer; a glimpse of the latter is seen between Leyden Jars and small transformer. The bottom ends of coupling and variometer .helices .are seen at top of photograph. Hiver. dose to Perth. 'l'he traffic )1andled by these two ,:;tations rm1s rnto mauy thousands of words per "!1m1m: and the· operators at both stat 1~11:-; must needs be exprrienced men ~k1ll ecl i11 both Radio ancl T.mndline telegraphy. '' R A b 1 6 u After we had a good look over the grounds, and tried to summon up sufficient courage to climb the mast, wc were taken in hand by Mr. G. F. Chilton, officer in charge, and conducted to the engine-room, a large building· standing some yards apart from the operating quarters. A Page. 101 first, two large motor generators made by G. ·weymouth Pty., Melbourne. These machines are duplicates-each set consisting of a 100 h.p. 440 volt 3 phase induction motor, directcoupled to a 60 K.W. 800 volt D.C. generator. The third set, also supplied by W eymouths, is a motor-gene- Main Operating Room VIS Operator on left (Mr. Hodges) is seen "tuning in.'; · Special Receiver has a range c,f from 300 to 14,000 metres. The well-known Expanse "B" is being used for reception. On the right is Mr. Dale despatching radios received from ships by telegraph to the G.P .. O. for delivery. During certain periods of rush traffic two operators are on ·duty together. The four manual keys on operating table from left to right are high-power key (operating relay key), low-power key, telegraph key, and buzzer key. notice board hanging on a cage-like screen just inside the engine-room sliding-doors with the significant word Danger thereon first met our eyes, but we were assured that such a ·warning was necessary only to the uninitiated. Inside the cage is housed the H.T. Transmission gear, consisting of the oil i-;,vitches built in brick cubicles, transformers, and other apparatus for reducing the 6000 volts 25 cycle 3 phase current from the N.S.W. Railways sub-station at Clyde to a pressure of 440 volts for dt'iving the various electrical m'.lchincs. Ontside the cage is the switchboard with Voltmeters, Ammeters, Wattmeters, Time-limit overload relays, oil switch levers, and ·,nain switches for distributing the ,.140 ,olts to the various circuits. Close to, and at right angles to this switchboard, and running almost the entire length of the engine-room is the controlling switchboard for operating the different machines. 'rl1is board is a magnificent piece of work, and consists of five panels, on which are mounted voltmet ers, ammeters, circuit-breakers and rheostats. Side by side, and facing their · respective panels, are, rator-a 20 h.p. 440 volt iucluc'.tion motor direct-coupled to a 12 KW. 100 volt D.C. generator. This sd is used for charging the 100 volt 600 amperehour set of T'udor accumulators from which the low-power machinery is operated; Facing the motor end of each machine is its respective starting pillar and water resistance sta:•·ter. At right angles to this charging set is first the motor-alternator set which supplies single-phase at 400 cycles for low-power spark transn1issio11. This unit consists of a G.E. 4.5 h.p. D.C. motor direct-coupled to a Weymouth 2.K.W. 400 cycle alternator. Alongside this unit i,:; a D.C. Motor-Generator set, made by the Ranclwick '\Vire] ess and Electrical Works. It con,:; ists of a 10 h.p. 100 volt D.C. motor clirect-coupred to a 7 K.W. 460 volt generator. This set is used for supplying D.U. to the low-power arc set. The Tudor accumulators supply the power for driving either of these machines, and both are stopped and
 * c:tarted from the operating room by

meaus of the automatic starter on subsidiary switchboard on their right. The solenoid for operating the starter handle is actuated by the operator

closing a small switch in operating room. A dash pot exercises an antagonistic pull against the attracting force of solenoid, and so ensures au even motion. The solenoid is necessarily subjected to a heavy current for a few seconds, until the handle is full on, by which time a spring contact is forced open, thereby inserting "RADIO" nator; belt driven by a 75 h.p. 4 cylinder Gardner Kerosene engine, or alternatively by a G.Ij].C. 60 h.p. 3 phase induction motor. The starting pillar and water resistance starter for the latter are facing the motor end. The alterantor can be driven by either engine or motor within a few minutes by simply changing the belts. Thus, Engine Room and Power House VIS shows Mechanic (Mr. Cookson) starting up 12 K.W. Weymouth Generating Set. The two Machines to the left are 60 K.W. Weymouth Motor Generator Sets. To the right is the main D. C. Switchboard. In the background, marked "Danger," is the High Tension Supply Cage wherein is contained the transformers, etc., conve·rting 6000 volts 3 phase 25 cycle to 440 volts for use with high-power machines. a lamp in series with the solenoid, and enabling it to remain in circuit for an indefinite period without risk of burning out. The starter arm, mice in position, also closes the blocking relays and other protective devices, so that the machine cannot be subjected to load until at full speed. The last set on this end of the mgine-room is a 20 h.p. Maritime In-ternal Combustion engine directcoupled to a 11 K.W. D.C. Generator. 'l'his engine is started on benzine, and by an ingenious arrangement can be run on kerosene after a minute's running. This is an auxiliary charging unit, and can be started up within a few minutes for charging the accumulators, thus making the station independent of a breakdown in power supply. The station is thus able to communicate with ships at sea, despite strikes, lockouts or other industrial troubles. On the other side of the engineroom, and occupying almost the whole length is the 35 K.V.A., A.E.G. Alteras in the case of the smaller set a strike or a breakdown in power s~pply would not prevent high-power transmission from being carried out. 'l'he Gardner engine is started by compressed air, and at the end of the shaft is a fast and loose pulley arrangement for driving a small air compressor to feed air reservoir after each start. This set is used for highpower spark transmission. Before passing out of the engineroom attention was attracted by another switchboard, on top of which was a frequency meter. This indicates the frequency in cycles delivered by the alternator, and is operated by an eccentric piece of iron on the end of the alternator shaft. The revolutions of the eccentric cause fluctuations in the magnetic field of a small solenoid close to it,. and the resultant pulsations are conveyed to the interior of the instrument, and caused to act inductively on a series of small reeds, each of which has a definite natural period of vibra- May 30, 1923. tion. The frequency corresponding to each reed is marked in regula1· progression on a horizontal scale, above which is a longitudinal aperture through which each reed is plainly visible. When the frequency coincides ( allowing for a factor, of course) with each reed according to the speed of the alternator, these reeds vibrate, and a demonstration which was given afforded a clear illustration, and showed how sensitive and reliable the instrument is, and how the engineer is able to control the frequency to a nicety, a vital point in this system of spark transmission. Queer, bottle-shaped standards, which were lying close to this board, turned out to be bottle screw-jacks, used for raising the mast, if necessary, to replace or renew the glass insulators underneath · the mast. One is inserted under each of the three legs of the huge mast, concrete pillars being built at the correct height for the purpose, and by using long spanners on each of these jacks the mast can be raised. Next we looked over the batteryroom, adjoining the engine-roo~1, where two rows of double Tudor cells ( 50 in all), making a 100 volt · set, are symmetrically arranged, with both sides of each row easily accessible for inspection or repair. This set was installed in 1913, and to the credit of those responsible for its upkeep, is still in first-class condition, and by no means exhausted. In a shed adjoining this room is the plant for 100 Volt Storage Battery, 650 ampsre hour capacity. Type J18 Tudor cells. This battery supplies power for all the low-power machines and equipment, and the lighting system for the station buildings and staff's quarters. lnsta, lled 1913. Mechanic is seen taking readings after charge. distilling water, it being necessary to add pure water to the accumulators from time to time to compensate for evaporation.

The last portion of the engine-room building is a workshop and store. Jiere are stored the various spare parts for renewing the different apparatus. The ticking of a telegraph sounder aroused curiosity, and it was explained that a local practising set was being operated from the main Auxiliary Operating Room VIS 3 K.W. arc transmitter on right. Central panel on left for regulating speed of gene rator and output. Just underneath the radiation meter is the starting resistance which also connects up relay key, solenoid for methylated bon, and pump for water circula tion, spirits drip, motor for revolving carand on last contact has connected arc to aerial. telegraph instrument by the mechanics during lunch hour. The senior mechanic already holds his first-class certificate as operator, and the other mechanic is going strong with the same end in view. Passing out of the engine-room we entered the operating building, which is divided into three rooms. At one end of the adjoining verandah is the O.I.C. 's office, and at the other end a bathroom. The first room contains the 3. K. W. Arc transmitter, and a receiving panel for use in conjunction therewith. This set can be started up in a few minutes, and has a range of several thousand miles. The manual key operates a relay, which, when the key is depressed, connects the arc circuit to the aerial, and when released, to an artificial circuit having the same period as .aerial and earth. This method of signalling is sometimes known as the  back shunt system, and when transmitting by same the '' marking wave only is radiated, and the  back wash,'' or spacing wave, usually characteristic of the arc system, and sometimes found difficult to tune out, is absent. A spacing· coil is provided, and -can be connected up in a few "RADIO" . minutes if desired. A small variometer in the aerial circuit, the variation of which makes a small change in the emitted wave length, is used to form a kind of "attention" signal at the receiving station by a heterodyne effect in case the receiving station is not tuned exactly to the proper adjustment. Alongside the arc set is the controlling switchboard for same with meter circuit-breaker, etc. Before leaving this room we were shown the starting device, which by reducing starting resistance after ' 'striking the arc finally on the out'' position, disconnects the receiver and connects the aerial to arc circuit. The receiving panel on the right of the arc transmitter has a tuning range from 250 metres to 18,000 metres, and it performed excellent work during the war in regularly intercepting signals from European, Asiatic and American stations. The next and middle room is the main operating office where the operator is kept busy exchanging · traffic with ships. The switchboard on the left hand side is for controlling the high-power transmission, and is fitted with main switch blocking relays, Page 103 occupying a prominent position. This receiver does excellent work, and communication with ocean-going vessels, particularly the Niagara, Tahiti, and other trans-Pacific ships haR been maintained up to distances of 4000 miles. Night after night traffic is exchanged with ships over a thousand miles distant, whilst the reception of signals from ship stations ·west of Perth is a common occurrence. Recently signals were received clearly from the Sophocles when that vessel was 3500 miles distant. To the left and just above the operator is the radiation meter, and just below same is a handle for changing from lowpower spark to buzzer transmission, the latter being used for working ships at close range. Close to this is the telegraph sounder, and on the operating table to the right of the operator are the manual keys. First the key operating high-power relay key, the telegraph key, lower-power key, then key for operating buzzer transmitter. In a convenient poi:;ition just above the table on the left is the Rend-receive switch handle, which ·opens and closes the transmitting ci1·cuit, and on the table near same is the Engine Room and Power House VIS. Shows 35 K.V.A. Alternat9r, 500 cycle, separate ly excited and belt-driven by 60 h.p. 3 phase G.E.C. motor. Mechanic is at starting pillar. To the right is the switchboard with main supply switch, frequency meter and H.F. protectors. In the background is 75 h.p. 4 cylinder Gardner engine, an auxiliary for driving alternator in case of power supply being ·cut off. This is the generating set used for high-power transmission. voltmeters, ammeters, fuses, etc., for D.C. and A.O. circuits. On the operating room table is the valve receiver, ·with a range of from 400 to 14,000 metres, and the wellknown ' 'Expanse B ' ' Valve is seen. switch for closing· the automatic starter circuit in the engine-room. The send-receive switch also closes one side of the transformer primary in addition to closing the transmitting circuit and opening. the receiver circuit, but

the latter is further protected by means of a small micrometer gap across aerial and earth leads. · Everything is arranged for rapid and reliable working, and to see the set in operation convinces one that communication with mobile stations, such as ships at sea, has, indeed, reached a high standard. A message is lodged at any post office in Australia, and if the ship for which it is intended is in touch with Sydney Radio the message passes over the land line, and is received by the operator. on c1nty there, who must, of necessity, be a skilled telegraphist, in addition to being qualified as a radio man. Whilst inspecting the operating 1·oom the telegraph instrument commenced clicking, and instantly the operator started writing rapidly. The sounds would be meaningless to the uninitiated, but to the operator they represented a message of perhaps vital importance. A second after the message is received the operator half-wheeL<; in his chair, pulls a lever, moves a switch, and presses the sending key. · A series of muffled squeaks distinguishable to the initiated as dots and dashes, discloses that a message is being sent to one! o.:' the Australian ships. A momer;t later the -:hip responds, and gave the ' ' go ahead'' sig- 11al. The vessel was the Ulimaroa, a day out from Auckland. The message transmitted to her came over the land line from somewhere in West Australia, and ,.vac; addressed to a passenger on the ship. One '.vonrler,; if the recipient Wi\R able to viimalise tlw route traversed by hifi message. First it was flashed over thr- trans-continental telegraph line, thence through the post offices in the various capital cities to Sydney Radio, from where, in a fraction of a second, it was trans-mitted to the ship. To the operator it was all part of the day's work, hut to onlookers it provided food for wonder and admiration. "RADIOH From the operating room we were conducted to the high-tension room, so called because everything there is subjected to high voltage. We were first shown the transformers, in which the voltage is stepped up in the ratio of perhaps 100 to 1-that is, to the alternating current supplied by the respective machines in the engineroom, whence it is conducted through underground cables. It is then passed through the primary windings of transformers, at, say, 200 volts, and is delivered from the secondary terminals at, say, 20,000 volt;. The need for good insulation is aptly illustrated by the large porcelain pillars on the top of the transformer. This voltage is applied to the leyden jar condensers arranged in banks of six series-parallel. Only three such banks are used for low power, but the whole system is put in circuit for high-power transmission. The spark gaps of the quenched type are arranged on racks in, six hanks of sixteen each, and underneath the racks are motorblowers for cooling the gaps when on high pm,ver. Immediately above the gaps are the helices for tuning and coupling, and also the varioniete:rs; provision bei1ig made to change to various wave lengths very quickly by simply plugging into certain sockets marked with the corresponding wave length. By means of a pulley control from the operating room the coupling can be varied, and fine adjustments made in aerial tuning to correct the wave length and effect the best transmission. A change from the normal wave length, 600 metres, to several other wave lengths up to 2,500 metres can be made in a few moments. The send-receive switch, magnetic rela.y for closing transformer circuit, and low frequency chokes are in one corner of the room, and close to them are the relay keys operating high power. In another corner of the room May 30, 1923. 1s the small rotary buzzer trall,',mitter, and also the low-power transformer. Sydney Radio holds a rather unique receiving record in having a long-distance transmitting range. '\Vhen the present officer in charge was previously at this station-from 1912 to 1915-'-as senior operator, he intercepted a message from the Anstral- ic1r-a German cargo boat-at n cfo,tance of 4190 miles west of Sydney. In those days valves were unknown, and the signals were received on a crystal. So far as is known, thii,; was the world 's record for low-power spark reception on 600 metres, and we have not hearcl of it having been beaten. In these days of valve reception, especially with multi-stage audio and radio amplification, such distances may not be regarded as unictne, but the incident mentioned serves to show that a: crystal r eceiver intelligently operated is not to be despised. Before leaving the Station we were shown over the quarters provided for the staff, the:,;e being situated at the top of the static1~ grounds facing the road. Each house is comfortab'le, and contains all possible conveniences, inclucling electric light, which ii,; supplied by the statio1; battery. Each occupant has a telephone connected to a miniature switchboard in the openl.1:ng l'J011' and the ,vhole arrarigP.ment ma]rn;, for comfort and conveirieP.ce. Readers of this article who kno\\' Sydney Radio by repnfation w1 ·i:, henceforth, have a new c:onr.eption of the Station and its work. 'l'he th011~ands of amateurs ,vho h~ar VIS working every night will unquestionably' be glad to learn srm1ething of t'ie equipment of the station, which tn them, represents the highest standard of efficiency, so far as N.S.W. is concerned at the present time.

P.109 - Commonwealth Controller of Wireless
'''Commonwealth Controller of Wireless. Mr. Malone's Distinguished Career.'''

It may be confidently asserted that there is not one out of the thousands of experimenters in Australia to-day who is not familiar with the name of the Controller of Wireless (Mr. J. Malone). To many of them he is known personally, and all who can claim his acquaintance are unanimous in the opinion that no better man could have been chosen for the important and responsible position which he now fills. Mr. Malone possesses an accurate and sympathetic understanding of the many problems with which at times he is faced. Those who know the volume of work he is called upon to perform are able to appreciate the difficulties he is frequently up against. It is only reasonable to expect that the administration of an Act dealing with such a new and technical subject as wireless should present many difficulties at the outset. That these difficulties have not been greater is a tribute to Mr. Malone's ability as an administrator, and the sterling service rendered by his assistants and deputies in the various States. A brief sketch of Mr. Malone's career appears herewith, and it affords convincing proof that by temperament, ability and experience, he is well fitted to occupy the position of Controller of Wireless. Mr. Malone joined the Post & Telegraph Department at Lismore, New South Wales, as Telegraph Messenger in 1898. Two years later he was appointed as a Relieving Officer. In 1906, as the result of a competitive examination, he joined the Engineering Branch of the Postal Department in Sydney. Between that time and 1915 he occupied various engineering positions in Sydney, and also acted as District Engineer at Goulburn. Later on he was Engineer for Lines in Queensland. Shortly after the outbreak of war he enlisted, and was immediately appointed Instructor in Wireless at the Wireless School at Moore Park, Sydney. During his period of active service he was in charge of all A.F.C. Wireless activities in France, and was awarded the M.C. After the Armistice was signed he undertook the study of wireless and other kindred engineering subjects for 12 months in Europe. During that time he mis at the R.A.F. Wireless Experimental Establishment at Biggin Hill, and also at the Signals Experimental Establishment at Woolwich. He returned to Australia, via the United States of America and New Zealand. Shortly after his return he was appointed Deputy State Engineer at Perth; and, later, when the Postmaster-General's Department took over the Radio Service from the Navy Department he was brought from Perth to take charge of it. He continued in that position until May, 1922, when by reason of the agreement entered into between the Government and Amalgamated Wireless (A'sia) Limited, the commercial activities were handed over to the control of the Company. During the time Mr. Malone was in charge of the Radio Service he prepared and obtained approval for a reorganisation scheme to be applied to all Coastal Radio Stations. This was not proceeded with, however, owing to the transfer already mentioned. Mr. Malone's next appointment was as Controller of Wireless in the Postmaster-General's Department, and when a short time ago the administration of the Wireless Act was handed over to the P.M.G.'s Department he was elevated to the position of Chief Manager of Telegraphs and Wireless for the Commonwealth. In that capacity he acted as adviser to the Commonwealth Government on all wireless matters, and is the officer responsible for the Wireless Act and Regulations. During the negotiations leading up to the agreement between the Government and Amalgamated Wireless Limited, Mr. Malone acted as technical adviser to the Parliamentary Committee which investigated the proposals prior to the agreement being signed. The present Wireless Telegraph Regulations were prepared by Mr. Malone, subsequent to his appointment as Controller of Wireless. He is a member of the Institute of Radio Engineers, the Institution of Electrical Engineers, and the American Institute of Electrical Engineers.

(Start Photo Caption) AUSTRALIA'S CONTROLLER OF WIRELESS — Mr. J. Malone, M.I.R.E., M.I.E.E., M.A.I.E.E. (End Photo Caption)

P.113 - Mr. J. H. A. Pike's Station
'''Mr. J. H. A. Pike's Station. Set on which American Signals were heard.'''

The complete receiver about to be described was designed and built in an endeavour to provide an instrument for the reception of very weak signals, such as one would expect in the Trans-Pacific Test. As the time at my disposal is very brief, I will not attempt to give a detailed description, but will reserve constructional details for a later article. The instrument is a universal receiver that can be used for all wave lengths simply by changing different standard plugs in the coils. Since signals from Major Mott, U.S.A., were received, two additional stages of high frequency amplification have been added, and it now consists of eight valves — five amplifying at high frequency, detector and two low frequency amplifiers. An advantage of this instrument is the easy means whereby it is possible to change from one combination of valves to another; either one or any combination up to five high-frequency valves with detectors may be used, or detector alone, or with one or two stages of audio or low frequency amplification. The instrument was commenced less than three weeks before the tests were timed to commence, and it was only finished after working well into the small hours of the morning, with the valuable assistance rendered by Mr. A. L. McCredie, of Epping. To make sure of completion on time it was decided to use as many standard parts as possible, and with the exception of the vernier condensers for tuning anode circuits of H.F. valves, and other small fitments, most of the apparatus consists of standard articles. For coupling the H.F. valves the tuned anode circuit was adopted as from past experience, I have found this method far superior to many others tried. This method of coupling has many advantages to recommend it; there is no trouble regarding the design of transformer, and tuning is easily attained by means of a single variable condenser in each circuit, the inductance being varied by different plug-in coils. Few experimenters seem to realise that When reaction is introduced into a circuit its selectivity is greatly increased, and, therefore, the tuning is much sharper. In H.F. amplifiers a certain amount of reaction takes place between the inter-valve circuit and the grid circuit of the next valve, this being due to the small capacity existing between the grid or plate of each valve. It open happens when reaction is introduced into the tuned anode or plate circuit that unless a means of accurately tuning that circuit is provided, signals are weakened instead of being strengthened. This explains why many so-called H.F. amplifiers weaken incoming signals when they should strengthen them. By consulting the photographs accompanying this article, it will be observed that a standard three-coil holder is used, different wave lengths being tuned by substituting various duo-lateral or other coils. A series parallel switch is provided in the secondary circuit instead of the customary primary circuit, so that a direct coupled circuit can be used when condenser is in series and loosely coupled when in parallel, a small two-way switch being provided to the left of the series-parallel switch to throw aerial into either circuit. Vernier condensers are provided in both primary and secondary circuits. This is essential in short wave work, as less than a degree on the dial of an ordinary condenser will often cause signals on short wave lengths to disappear. Kellogg condensers are used owing to their sound design of bearings, and also being noiseless in operation, an inherent fault in many so-called variable condensers. Bakelite is used for the panel, which measures 38 inches by 15 inches by ¼ inch thick. This is far superior to ebonite, both in rigidity and absence from warping tendencies. A plan showing the disposition of the various components was prepared, and the position of all holes marked. These were then drilled and tapped where necessary. The next step was to remove the shiny surface of the bakelite with fine emery or glass paper, and a final rubbing with stone. When this operation is completed it will be found to have a smooth, even finish without scratches, its insulating qualities being also improved. It can be easily imagined that a panel of the above dimensions is very unwieldy and difficult to hold while squaring-up operations are being executed, so the method adopted of fastening it to the bench by means of wood screws through any suitable hole may be of interest. The valves are placed at the rear of panel, so that their glare when in operation will not bear directly on the operator, as this is very detrimental to the eyes and also has a marked tendency of making one very drowsy, especially when searching for weak signals on the "midnight patrol." Near the top of the panel will be noticed five two-way switches with a dead stud in the centre. These are used in conjunction with their respective rheostats for switching in or out the various H.F. stages. To use detector valve alone the four switches from left to right are put in central position, the last one is turned to left; when one stage of H.F. is used the second switch from right is moved to the left, and last switch (marked No. 1) is moved to right and so on, as each stage is added. On paper it seems a lengthy operation, but in practice it takes far less time than to describe. The plug and jack method of putting the 'phones in either detector first or second stage of audio-frequency amplification is used, as the operation is very quickly accomplished. Separate rheostats with an off position are provided for each H.F. valve, and a vernier rheostat for detector, this being a very useful acquisition; one rheostat controls the two low frequency valves and a plug is used to cut in or out filament of second stage. A potentiometer of 400 ohms resistance is provided as a means of putting either a negative or positive potential on grids of H.F. valves, the ends of winding being connected across "A" battery and sliding contact being connected to grid of fifth stage H.F. valve and to grid leaks of the remainder, this refinement having been found necessary to the successful operation of the instrument. Along the centre of the panel will be noticed five standard coil-plug holders for the necessary coils being used in tuned anode circuits, each holder being mounted at right angles to preceding and following ones, so that any tendency to "howling" may be illustrated, as a minimum of coupling is obtained between each circuit. Underneath these coil holders are found the dials which control small variable condensers of about 0.002 mfd. capacity for tuning purposes. Each coil will cover a certain fixed range of wave lengths. The coils in this set for a range of 200-460 metres consist of De Forest duo-lateral of 25, 50 and 75 turns. Other makes are sometimes used, but a coil of one make varies considerably in its inductance value to that of another make, so one pattern throughout is usually adopted. A reversing switch is provided for the re-action coil, as when each further stage of H.F. amplification is added the reaction coil must be reversed. A double pole single throw snap switch is μsed to cut in or off "A" and "B" batteries in one operation. Naturally the chief feature in a set of this description is the class of valves used, for high frequency valves having low capacity and noiseless operating characteristics are necessary. Both V24's and Mullard K.A. types give every satisfaction, Mullard being used at present, as they function on 3.5 volts on filament, thus giving them preference, as my chief source of filament supply is 4 volt storage batteries. A Mullard "ORA" is used for detecting and V24's for low frequency amplifiers. In operating a set of these dimensions it must be clearly understood that no more valves than necessary for reception of clear signals should be used as with all valves burning, 6 amps. are drawn from battery, and as I don't possess a "Homecharger" the task of heavy weight lifting is not indulged in more often than necessary.

(Start Photo Caption) Mr. J. H. A. Pike at his Experimental Radio Station at Epping. (End Photo Caption)

(Start Graphic Caption) Plan showing Panel Arrangement used by Mr. Pike. (End Graphic Caption)

(Start Photo Caption) This Photo shows Back of Panel Receiver made by Mr. Pike. (End Photo Caption)

P.115 - West Australian Work
West Australian Work. (By our Special Representative.)

After much pioneering work Radio has at last found a lodging place in popular favour amongst the people of West Australia. It will be interesting to indulge in a brief but comprehensive survey of the progress made by local enthusiasts who have been carrying out transmitting work. There are about half a dozen of these in and around the city; but for this issue comment will be confined to the installation owned by Mr. W. E. Coxon, of 306 Bulwer Street. Gauged on radio movements in this State, this is a pretty powerful plant, and being of a style all its own, is the result of the owner's several years experimental work. After overcoming the usual initial difficulties and adapting his set to local conditions, Mr. Coxon · commenced transmitting, and in the stilly watches of a certain night several months ago local enthusiasts received a tremendous shock when, in operating their tuning-in gear they suddenly picked up the strains of music Excitement ran high, and many attempts to guess its origin were made, some even suggesting New York, but everybody was agreeably surprised when next morning they discovered that the music came from Mr. C:oxon's experimental station. A few nights ago the writer visited the station, and was conducted to a room containing a maze of plugs, valves, condensers, switches, and a tangle of wires, meters, telephones, and other apparatus. Experiments in the transmission of music, speeches, etc., were in full swing. l\Ir. Coxon uses--10 watts on a wave length of 420 metres, and his music is received clearly on crystal sets at a distance of fifteen miles, while those possessing single valve receivers get good results up to 50 miles. Even at this distance, however, interference is experienced from VIP signals on 600 metres. Only one valve is used as a radiator, modulation being covered on a method devised by Mr. Coxon. The regulation is good, either expauded or softened sound being always under eontrol, so that listeners-in receive anything from almost a whisper to a large-sized shout without trouble. No iron core coils are used, and this gives perfect reproduction. 'rhe source of power is a motor generator giving up to 100 watts, and there are two windings, each on separate commutators. One winding generates 15 volts, and is used for excitation, while the high tension is wound over the first and insulated with oiled silk, to withstand 1,000 volts. The armature, however, only measures 13 inches in diameter · and 8 inches in length, and it is scarcely creditable that such a baby is capable of providing power necessary for the transmission of signals over a thousand miles.

P.116 - Club Notes & News
West Australian Work. (By our Special Representative.)

P.119 - Queries Answered
West Australian Work. (By our Special Representative.)


text:
LMIs in Control/Click here to continue/Applications of Linear systems/Hinf LMI Satellite Attitude Control

This is a $$H_{\infty}$$ LMI for Satellite Attitude Control. Satellite attitude control is necessary to allow satellites in orbit accomplish their mission. Poor satellite attitude control results in poor pointing performance which can result in increased cost, delayed service, and reduced lifetime of the satellite.

The System
The full derivation of the system from first principles is accomplished in the companion LMI for $$H_2$$ Satellite Attitude Control. The link to that page is at the bottom with the references.

Continuous Time:

\begin{align} I_x\ddot{\phi}+4(I_y-I_z)\omega _0^2 \phi + (I_y - I_z - I_z)\omega _0 \dot{\psi} &= T_{cx} + T_{dx}\\ I_y\ddot{\theta}+3(I_x-I_z)\omega _0^2 \theta &= T_{cy} + T_{dy}\\ I_z\ddot{\psi}+(I_x+I_z-I_y)\omega _0 \dot{\psi} &= T_{cz} + T_{dz}\\ \end{align}$$

The above model was derived by substituting satellite attitude kinematics into the attitude dynamics of a satellite. The following are definitions of the variables above:

 * Moments of inertia about the corresponding axis: $$I_x, I_y, I_z $$
 * Euler Angles: $$\phi,\theta,\psi $$
 * Disturbance Torques (flywheel, gravitational, and disturbance): $$T_c, T_g, T_d $$
 * Rotational-angular velocity of the Earth: $$ \omega _0 = 7.292115x10^{-5} \text{ [rad/s]} $$

The state-space representation of the system can be found by the following steps. Let

\begin{align} x &= \begin{bmatrix} q & \dot{q} \end{bmatrix}^T,& z_{\infty} = 10^{-3}M\ddot{q},& z_2 = q,\\ \end{align}$$

Introduce the notations

\begin{align} I_{\alpha \beta}&=I_{\alpha}-I_{\beta}, & I_{\alpha \beta \gamma} = I_{\alpha} - I_{\beta} - I_{\gamma}\\ \end{align}$$

where $$ \alpha, \beta, \gamma $$ stand for any element in $${x,y,z}$$. Then the state-space system is:

\begin{align} \dot{x} &= Ax + B_1u+B_2d \\ z_{\infty} &= C_1x+D_1u+D_2d \\ z_2 &= C_2x \\ \end{align}$$

where the matrices in the above state-space representation are defined as follows:

\begin{align} A = \begin{bmatrix} 0 & 0 & 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 0 & 1 & 0 \\               0 & 0 & 0 & 0 & 0 & 1 \\                \frac{-4\omega_0^2 I_{yz}}{I_x}  & 0 & 0 & 0 & 0 & \frac{-\omega_0 I_{yzx}}{I_x} \\ 0 & \frac{-3\omega_0^2 I_{xz}}{I_y} & 0 & 0 & 0 & 0 \\ 0 & 0 & \frac{-\omega_0^2 I_{yx}}{I_z} & \frac{\omega_0 I_{yzx}}{I_x} & 0 & 0 \end{bmatrix}\\ \\ B_1 = B_2 = \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \\                           0 & 0 & 0 \\                            \frac{1}{I_x} & 0 & 0 \\ 0 & \frac{1}{I_y} & 0 \\ 0 & 0 & \frac{1}{I_z} \\ \end{bmatrix}\\ \\ C_1 = 10^{-3} \times \begin{bmatrix} -4\omega_0^2I_{yz} & 0 & 0 & 0 & -\omega_0 I_{yxz}\\ 0 & -3\omega_0^2 I_{xz} & 0 & 0 & 0 & 0\\ 0 & 0 & -\omega_0^2 I_{yx} & \omega_0 I_{yxz} & 0 & 0 \end{bmatrix}\\ \\ C_2 = \begin{bmatrix} I_{3x3} & 0_{3x3} \end{bmatrix} \\ \\ D_1 = 10^{-3} \times L_1, D_2 = 10^{-3} \times L_2 \end{align}$$

The Data
Data required for this LMI include moments of inertia of the satellite being controlled and the angular velocity of the earth. Any knowledge of the disturbance torques would also facilitate solution of the problem.

The Optimization Problem
The idea is to design a state feedback control law for the previous satellite state-space system of the form

u = Kx $$

This control law is designed so that the closed-loop system is stable and the transfer function matrix from disturbance to output

G_{z_\infty d}(s) = (C_1+D_1K)(sI-(A+B_1K))^{-1}B_2+D_2 $$

satisfies

$$
 * G_{z_\infty d}(s)||_{\infty} = (C_1+D_1K)(sI-(A+B_1K))^{-1}B_2+D_2

for a minimal positive scalar $$\gamma_{\infty}$$ which represents the minimum attenuation level.

The idea here is to attenuate the disturbances as much as possible while still maintaining the ability of the satellite to track. This minimum attenuation level is found from the LMI in the following section.

 * Objective: Hinf norm
 * Variables: Controller Gains
 * Constraints: Satellite Attitude Dynamics and Kinematics. Maximum safe rotational rate of Satellite, maximum jet pulse thrust

The LMI: $$H_{\infty}$$ Feedback Control of the Satellite System
Duan and Yu approach the $$H_{\infty}$$ satellite system as follows. The minimum attenuation level from disturbance to output can be found by solving the following LMI optimization problem.

\begin{align} \\ &min \gamma_{\infty} \\ \\ &\text{s.t. } X > 0 \\ \\ &\begin{bmatrix} (AX+B_1W)^T+AX+B_1W & B_2 & (C_1X+D_1W)^T \\ B_2^T & -\gamma_{H\infty} I & D_2^T \\ C_1X+D_1W & D_2 & -\gamma_{H\infty} I \end{bmatrix} < 0 \\

\end{align}$$

which is the same as Theorem 8.1 in Duan and Yu's Book, the solution to the $$ H_{\infty} $$ problem.

Conclusion:
The Duan and Yu textbook takes as typical values of the satellite moment of inertias as:

\begin{align}

I_x = 1030.17 kg\cdot m^2, I_y = 3015.65kg\cdot m^2, I_Z = 3030.43kg\cdot m^2\\

\end{align}$$

They then proceed to solve the optimization problem to find a controller gain that yields an attenuation level of 0.0010. Though this value is very small and represents very good attenuation the optimized controller pushes the poles of the closed loop system very close to the imaginary axis, resulting in slow oscillatory behavior with a very long settling time.

To address this a second approach was used by the authors which involves modifying the final LMI in the expression above and requiring that it be constrained as follows

\begin{align} &-I < \begin{bmatrix} (AX+B_1W)^T+AX+B_1W & B_2 & (C_1X+D_1W)^T \\ B_2^T & -\gamma_{H\infty} I & D_2^T \\ C_1X+D_1W & D_2 & -\gamma_{H\infty} I \end{bmatrix} < 0 \\ \end{align}$$

These results are planned verified in the linked code implementation using YALMIP, whereas the authors took advantage of the MATLAB LMI Toolbox to achieve their results.

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

Related LMIs
Links to other closely-related LMIs

 * H2_LMI_SatelliteAttitudeControl
 * Optimal_Output_Feedback_Hinf_LMI
 * Full-State_Feedback_Optimal_Control_Hinf_LMI

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


text:
History of wireless telegraphy and broadcasting in Australia/Topical/Publications/Radio in ANZ/Issues/1923 06 13

Link to Issue PDF
WorldRadioHistory.com's scan of Radio in Australia and New Zealand - Vol. I No. 06 - 13 June 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 06 13

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. — JUNE 13, 1923 — No. 6

(Start Graphic Description) Miss Edith Clifford, vaudeville artist, who undertakes daily weight-reducing exercises to radio music.— "Wide World" Photo (End Graphic Description)

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

P.121 - Contents Banner
RADIO in AUSTRALIA & NEW ZEALAND Incorporating "Sea, Land and Air"

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

CONTENTS

Volume I.  JUNE 13, 1923    Number 6

P.121 - Contents
CONTENTS.

 * Radiotorial . . . Page 122
 * Australia's Future Wireless System . . . Page 123
 * Experimental Transmission Tests . . . Page 123
 * Continuous Wave Transmission . . . Page 124
 * Broadcasting Conference . . . Page 126
 * Queensland Insurance Company Radio Club . . . Page 127
 * Experimental Work at Manly, N.S.W. . . . Page 128
 * Waves from West Australia . . . Page 129
 * The Co-Relation of the Various Forms of Energy . . . Page 130
 * Tasmanian Activities . . . Page 132
 * Miss Lee White Entertains "Listeners In" . . . Page 133
 * Transmitting Licenses in South Australia . . . Page 133
 * The Experimenters' Corner . . . Page 134
 * New Zealand Wireless Development . . . Page 136
 * Radiofun . . . Page 138
 * Queensland Notes . . . Page 139
 * Club Notes and News . . . Page 140
 * Queries Answered . . . Page 143
 * Coastal Radio Service . . . Page 144
 * Movements of Marine Operators . . . Page 144

P.121 - 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.122 - Radiotorial
What the Conference Accomplished

It is yet too early to say whether the regulations to govern broadcasting in Australia, which were agreed upon by the recent Melbourne Conference, will achieve in practical operation the promise they now hold. Much depends upon how they are administered, and the extent to which those coming under them shape their activities. The Conference delegates set a good example to the rest of Australia by the whole-hearted manner in which they tackled the problem of framing regulations for the Minister's guidance. The difficulties confronting them were undeniably great, and few expected such a speedy and unanimous termination to the proceedings. It now remains for the result of their deliberations to be tested in actual practice. When that is done we believe that the scheme will reveal the fact that the regulations are the best possible suited to the peculiar needs and conditions of Australia, the army of experimenters, and the general public. Prior to the opening of the Conference the opinion was expressed in some quarters that special representation would be required to safeguard the interests of genuine experimenters. It was feared that unless this representation was forthcoming their interests would be subordinated to the purely amusement side of broadcasting by confining them to wave lengths practically useless for experimental work. Happily, this fear proved to be groundless. Without exception, the Conference delegates demonstrated their anxiety to do the best possible in the interests of all concerned, and a perusal of the regulations, as submitted for the Minister's approval, discloses that those who come under the heading of "experimenters" will in no wise have their activities curtailed. This is as it should be. In Australia, as well as in other countries, the experimenter deserves much credit for the progress made by wireless in recent years. It was not always as interesting and entertaining to dabble in radio, as it is at the present day. One does not require a long memory to recall the time when the man who put up an aerial and attempted to pick up signals was regarded in the light of a "crank." Much has happened in the last few years, and it would be a poor return for all the good work they have accomplished if the men who helped to "blaze the trail" were to be sacrificed on the altar of public amusement. No apprehension need be felt, however, that the regulations will operate to the slightest extent against the best interests of experimenters. The public will have its entertainment, the amateur his experiments, and the commercial possibilities of radio will be exploited to the fullest extent. That is the ideal which Australia must aim at, and there is no reason why it should not be attained. The Broadcasting Conference laid a good foundation.

When It Pays to "Go Slow"

Those who have been clamouring for the commencement of broadcasting in Australia are likely to have their desire gratified at an early date. The danger of a monopoly, which many people professed to fear, has proved quite illusory. When England lagged behind America in making use of the tremendous entertainment and educational possibilities of radio broadcasting there was the usual outcry from those who wish to imitate the "bull at the gate" act every time a new idea or invention comes to light. Fortunately, the authorities refused to be stampeded, and subsequent happenings have more than justified their apparent conservatism. England to-day boasts a broadcasting service, unquestionably not perfect, but far in advance of that which operated at the outset of the radio boom in America. True, the latter has since put her house in order, but only after she was taught a severe lesson. Chaos reigned supreme there for many months, and that the tangle was eventually straightened out is a tribute to the popularity of radio and its influence for good in the community. A discovery of lesser value would have gone under in the first few months, but radio emerged triumphant, and has since won its way into the homes of the people as a permanent institution. Australia now has an opportunity of enjoying all that is best in radio entertainment, and there is little doubt that the chance will be embraced with both arms. The broadcasting regulations will probably be gazetted at an early date, and all who desire to carry out the transmission of entertainment programmes will be free to proceed. It will, of course, be some little time before everything is working smoothly, and the highest point of perfection attained. That, however, need occasion no dismay. The future is ours to make or mar, and those who undertake to supply the public with programmes to its taste can be assured of an eager and appreciative audience. The stage is set, and Australia is eagerly waiting for the curtain to be lifted on the first act.

P.123 - Australia's Future Wireless System
'''Australia's Future Wireless System. Other Countries Point the Way. A Vision that will become a Reality.'''

THE average Australian, unless he be a radio enthusiast, has a very imperfect conception of what an up-to-date radio system is like, and how it works. In fact, few people realise that such a high standard of excellence has been attained in the application of radio telegraphy to the commercial needs of the different countries, as is the case in America, France and England today. In these three countries, and particularly the two first-named, there has been a very great advance in commercial wireless telegraphy during the past two years. There have been established in each of London, Paris, and New York, large central collecting and despatching offices for wireless messages to and from all parts of the world. In the heart of the city messages are being passed over the counter, and thence sent by automatic carriers into the middle of the telegraph office. Other messages are being received through telephones by expert telephonists, from all over the city and country to go by wireless. In . another section are automatic printing machines connected direct with offices of big trading firms and banks, 1r\1ich do a ]argc--amount of telegraphing; other busine:;;s houses are connected by the ordinary telegraphic ~ervice. By all these channels messages flow into the central traffic office. Jn the office there are tables where operators type out the messages on an ordinary typewriter keyboard. That automatically perforates a tape with the Morse code, and the tape runs through a machine at anything up to 120 words a minute. The machine, in turn, is connected to an over. land wireless transmitting station situated from 20 to 50 miles distant. At the transmitter station there is only a silent apparatus, with engineers who keep the gear running. The impuL,es coming over the land line at high speed operate the transmitter, sending the messages by ,vireless to a distant :;;tation. They come into the receiving station, anything between 20 and 50 miles away from a city-which station again contains 110 operators, but simply attendants who keep the apparatus in order-and with absolutely no sound whatever, are transferred on the landline to the addressee, or are received and telephoned into the city, where they are passed on by the land system for distribution at home, or by wireless to some other country. At the present time these high-speed circuits are working in Great Britain, the United States, Canada, Switzerland, France, Spain, and Germany. Services in other countries are being arranged now. In :B1rance they are conducting services to America, as well as European countries, and the new French station ( St. Assise) is designed to work with four distant countries simultaneously. · In addition to that they have got an intro-European station right in the heart of the citv where,' after the incoming wirelc signals have punched holes in the t ape according to the. Morse characters, • the tape is run at high speed through a machine which converts the Morse characters into printed letters. These messages, as they are cut off and pasted on to slips, are passed along an automatic band-conveyor to what is called the unpacking room. In that room there are clerks ,vith card indexes containing at least 40,000 code addresses, and as these messages come in with code-indicator addresses they are marked for proper dist ribution, either by telephone or otherwise. Switzerland has a service with England, and is arranging extension to other countries. Germany has two services working with America, and an intra-European station for communicating within and without Germany, capable of working thirteen different stations simultaneously. One modern wireless service to-day is carrying more than 20,000,000 p aid word,; per annum, and the chairman of one of the big cable companie:,; iu an addres:;; la,;t year referred to the great proportion of traffic between Europe and America which is now going by wireless.

Experimental Transmission Tests
ln order to enable the hundreds of experimenters who possess receiving ,ets to conduct tests, arrangements have been made by Mr. E. T. Fisk, 1Ianagino- Director of Amalgamated Wireless 0 (Aust.), Ltd., for one of the company's experimental stations m Sydney to transmit a programme on a wave length of 400 metres. For the present transmission will be carried out on. Tuesday evening only of each week, between 7.30 p .m. and 8.15 p .m., and will con,;ist of l.C.W., C.W. and telephone speech signals. The tests will be continued indefinit ely, and the number · of nights per ,veek may li ter on be increased.

P.124 - Continuous Wave Transmission
Continuous Wave Transmission.

P.126 - Broadcasting Conference
'''Broadcasting Conference. Important Resolutions Agreed to.'''

P.127 - Queensland Insurance Company Radio Club
Queensland Insurance Company Radio Club.

P.128 - Mr. F. C. Swinburne's Up-to Date Station
'''Experimental Work at Manly, N.S.W. Mr. F. C. Swinburne's Up-to-Date Station. Long Distance Reception.'''

P.130 - The Co-Relation of the Various Forms of Energy
The Co-Relation of the Various Forms of Energy.

P.132 - Tasmanian Activities
Tasmanian Activities. (By Our Special Representative.)

Tasmania has long felt the need of a Radio Club, and at a recent meeting in Hobart it was decided to form one. The initial success has far exceeded the expectations of those behind the move. The meeting decided that the Club should be known as the Tasmanian Division of the Wireless Institute of Australia. Mr. Robt. Nettlefold was elected Patron. Amongst the members are a number of well-known enthusiastic experimenters. Some very fine work has been done both in transmitting on low power and the reception of amateur signals from the mainland. The most outstanding feature of this work is that of Station 7AA, in charge of Mr. T. Watkins. Some time ago arrangements were made with the Victorian Division for a series of tests, Mr. Watkins being detailed by the Tasmanian body as its representative. Code signals were used throughout these tests, and out of the seven transmitting stations in and around Melbourne, the log kept by 7AA showed that the whole seven were received. Considering the low power used (approximately 6 watts) by these experimenters, it is a remarkable achievement. The seven stations were all copied, and their telephony heard distinctly, although only one valve was used. Since these tests Mr. Watkins has been successful in linking Tasmania with the mainland by means of his 5 watt transmitting set. This test took place at the latter end of April, and word was afterwards received from Melbourne that the signals were heard. Fuller details are being awaited with keen interest by experimenters in and around Hobart. The work of erecting a transmitting and receiving station at the Institute's Club rooms, Trafalgar Place, Hobart, is now in full swing. At an early date it is hoped to be able to communicate direct with the various other bodies on the mainland. To enable the Institute to carry on this work it will be essential to have the co-operation of as many amateurs as possible in our own State. Judging by the many applications for membership that have been received, the Council feels assured of success. A movement is afoot in the northern part of the Island to form a branch of the division at Launceston. Complaints have been made regarding the delay in issuing receiving licenses. It is hoped that this will be obviated in the near future.

AERIALS AND AIR TRAFFIC.
The delegate at the Broadcasting Conference, who unconsciously brought the element of comedy into the precinct of a tense atmosphere, by requesting that homing pigeons be protected against the threatened multiplicity of aerials, stoutly braved the hilarity that he created. The four hours of accumulated suppressed feeling was released upon him in the form of cheers and laughter, and with a force and spontaneity of a Leyden Jar. The delegate asked for corks to be strung on aerial wires, but it was pointed out that single wire aerials were not so numerous in Australia as in England — the country from which the delegate drew his information.

P.133 - Miss Lee White Entertains "Listeners-In"
Miss Lee White Entertains "Listeners-In".

At Mr. R. C. Marsden's Experimental Station (2JM) at Edgecliffe, Sydney, one Sunday evening recently Miss Lee White and Mr. Clay Smith, together with Hector St. Clair provided an entertainment for hundreds of "listeners in" throughout New South Wales. Miss Lee White sang several well-known songs from her musical revue, "Back Again," and Frank Charlton also rendered several vocal items. To secure a permanent record of the event Paramount Pictures cinematographed the whole performance. Mr. Marsden subsequently received reports to the effect that the concert was heard in Armidale, Tamworth, Mudgee, Inverell, Mandurama, Goulburn, Newcastle, and even in far away Toowoomba (Q'land) it was picked up on a single valve. It will be good news to all who enjoyed the first concert, and to others who did not have their sets ready that Miss Lee White and Mr. Smith will give a repeat concert at a later date, of which due notice will be given.

(Start Photo Caption) A Quaint Pose by Miss Lee White and Mr. Clay Smith of "BACK AGAIN," taken while singing songs from the popular revue into the transmitter of Mr. Marsden's Station (2JM). The above picture is enlarged from a motion picture negative of the Paramount Gazette, which filmed the event with the aid of hand flares. (End Photo Caption)

P.133 - Transmitting Licenses in South Australia
Transmitting Licenses in South Australia.

 * 5AC V. R. Cook, 57 John's Road, Prospect.
 * 5AD A. R. Snoswell, Harris Street, Exeter.
 * 5AE J. M. Honner, Alpha Road, Prospect.
 * 5AG W. J. Bland, Buller Terrace, Alberton.
 * 5AH F . L. Williamson, Dequetteville Terrace, Kent Town.
 * 5AV Wireless Institute, S.A. Division (C. E. Ames), 20 Grange Road, Hindmarsh.
 * 5AW Adelaide University, North Terrace, Adelaide.
 * 5BD F. E. Earle, 321 Fifth Ave, St. Peters.
 * 5BG H. A. Kauper, Guiney Road, Dulwich.
 * 5BI School of Mines (W. W. Honnor), North Terrace, Adelaide.
 * 5BN H . L. Austin, 8 Parade, Norwood.
 * 5BQ L. C. Jones, Carlisle Road, Westbourne Park.

P.134 - The Experimenters' Corner
The Experimenters' Corner.

P.136 - New Zealand Wireless Development
'''New Zealand Wireless Development. Marked Interest Displayed.'''

P.139 - Queensland Notes
Queensland Notes.

P.140 - Club Notes & News
Club Notes & News.

P.143 - Queries Answered
Queries Answered.

P.144 - Coastal Radio Service
Coastal Radio Service.

P.144 - Movements of Marine Operators
Movements of Marine Operators.


text:
LMIs in Control/Click here to continue/Applications of Linear systems/H2 LMI Satellite Attitude Control

This is a H2 LMI for Satellite Attitude Control

Satellite attitude control is important for military, civil, and scientific activities. Attitude control of a satellite involves fast maneuvering and accurate pointing in the presence of all kinds of disturbances and parameter uncertainties.

The System
The satellite state-space formulation is given in the $$H_{\infty}$$ LMI page for Satellite Attitude Control which is also in the applications section of this WikiBook. This section discusses the derivation of that state-space formulation based on first principles.

The attitude dynamics of a satellite in an inertial coordinate system can be described in terms of the time rate of change of its angular momentum and the sum of the external torques and moments acting on the system. That is:

\begin{align} \dot H&=T_c+T_g+T_d,\\ H&=I_b\omega\\ \end{align}$$

where the following variables are defined as follows:

 * $$T_c,T_g, \text{ and } T_d $$ are the flywheel torque, the gravitational torque, and the disturbance torque.
 * $$H$$ is the total momentum/torque acting on the satellite
 * $$I_b$$ is the inertia matrix/tensor for the satellite
 * $$\omega$$ is the angular velocity vector of the satellite.

The time derivative of the total angular momentum in an arbitrary rotating reference frame (such as the body frame of the satellite) is given by:

\begin{align} \dot H&=I_b\dot{\omega}+\omega \times (I_b \omega),\\ \end{align}$$

which takes into the account of the angular velocity of the rotating reference frame relative to the inertial reference frame where Newton's laws are valid.

Combining equations, collecting terms and choosing the principle axes of the spacecraft so that the Inertia Tensor is diagonalized yields the following equations of motion:

\begin{align} I_b \dot{\omega} + \omega \times (I_b \omega) = T_c + T_g + T_d,\\ \end{align}$$

Using the small angle approximation, the angular velocity of the satellite in the inertial coordinate system represented in the body coordinate system can be written as

\begin{align} \omega = \begin{bmatrix} \omega _x \\ \omega _y \\ \omega_z \end{bmatrix} = \begin{bmatrix} \dot{\phi} - \omega _0 \psi \\ \dot{\theta} - \omega _0 \\ \dot{\psi} + \omega _0 \psi \end{bmatrix} \\ \text{where } \omega _0 = 7.292115 \times 10^{-5} \text{ [rad/s]} \\ \end{align}$$

These equations form the basis of the state-space representation used in the H-inf LMI for satellite attitude control. For clarity, they are repeated below.

\begin{align} \dot{x} &= Ax + B_1u+B_2d \\ z_{\infty} &= C_1x+D_1u+D_2d \\ z_2 &= C_2x \\ \\ \end{align}$$

\begin{align} A = \begin{bmatrix} 0 & 0 & 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 0 & 1 & 0 \\               0 & 0 & 0 & 0 & 0 & 1 \\                \frac{-4\omega_0^2 I_{yz}}{I_x}  & 0 & 0 & 0 & 0 & \frac{-\omega_0 I_{yzx}}{I_x} \\ 0 & \frac{-3\omega_0^2 I_{xz}}{I_y} & 0 & 0 & 0 & 0 \\ 0 & 0 & \frac{-\omega_0^2 I_{yx}}{I_z} & \frac{\omega_0 I_{yzx}}{I_x} & 0 & 0 \end{bmatrix}\\ \\ B_1 = B_2 = \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \\                           0 & 0 & 0 \\                            \frac{1}{I_x} & 0 & 0 \\ 0 & \frac{1}{I_y} & 0 \\ 0 & 0 & \frac{1}{I_z} \\ \end{bmatrix}\\ \\ C_1 = 10^{-3} \times \begin{bmatrix} -4\omega_0^2I_{yz} & 0 & 0 & 0 & -\omega_0 I_{yxz}\\ 0 & -3\omega_0^2 I_{xz} & 0 & 0 & 0 & 0\\ 0 & 0 & -\omega_0^2 I_{yx} & \omega_0 I_{yxz} & 0 & 0 \end{bmatrix}\\ \\ C_2 = \begin{bmatrix} I_{3x3} & 0_{3x3} \end{bmatrix} \\ \\ D_1 = 10^{-3} \times L_1, D_2 = 10^{-3} \times L_2 \end{align}$$

The Data
Data required for this LMI include moments of inertia of the satellite being controlled and the angular velocity of the earth. Any knowledge of the disturbance torques would also facilitate solution of the problem.

The Optimization Problem
The optimization problem seeks to minimize the H2 norm of the transfer function from disturbance to output. Thus, we expect slightly different results than the H-inf case. Deriving the H2 control problem and setup also serves for useful setup for the mixed H-inf/H2 optimization that the book follows up with later.

 * Objective: H2 norm
 * Variables: Controller Gains
 * Constraints: Satellite Attitude Dynamics and Kinematics. Maximum safe rotational rate of Satellite, maximum jet pulse thrust

The LMI: H-2 Satellite Attitude Control
Duan and Yu use the following H-2 Satellite Attitude Control LMI to minimize the attenuation level from disturbance to output. Note that in the H2-case we are minimizing the integral of the magnitude of the bode plot transfer function whereas in the H-inf case the optimization is minimizing the maximum value of the bode plot magnitude.

To design an optimizing controller of the form

\begin{align} u=Kx\\ \end{align}$$

such that the closed-loop system is stable and the transfer function matrix

\begin{align} G_{z2w}(s) = C_2(sI-(A+B_1K))^{-1}B_2\\ \end{align}$$

satisfies

\begin{align} \|G_{z2w}(s)\|_2 < \gamma _2\\ \end{align}$$

for a minimal positive scalar $$\gamma_2$$.

This scalar is found from the solution of the following LMI

\begin{align} \\ \min &\ \ \rho \\ \\ \text{s.t. } &AX+B_1W+(AX+B_1W)^T+B_2B_2^T < 0 \\ \\ &\begin{bmatrix} -Z & C_2X \\ (C_2X)^T & -X \end{bmatrix} < 0 \\ \\ &\operatorname{trace}(Z)<\rho \\

\text{where } \rho = \gamma_2^2.

\end{align}$$

and the controller is given by $$K = WX^{-1}$$

Conclusion:
The LMI for H-2 Satellite Attitude Control comes up with a different attenuation value for the disturbance vs the H-inf problem which is expected. It also serves for good preparation for the mixed H2/H-inf problem that Duan and Yu cover in a later section. Though no implementation is included for the mixed H2/H-inf optimization problem it is interesting to compare the results of all three cases for the satellite attitude control problem.

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

Related LMIs
Links to other closely-related LMIs

 * Hinf_LMI_SatelliteAttitudeControl
 * H2OptimalOutputFeedback
 * Full-State_Feedback_Optimal_Control_H2


text:
History of wireless telegraphy and broadcasting in Australia/Topical/Publications/Radio in ANZ/Issues/1923 06 27

Link to Issue PDF
WorldRadioHistory.com's scan of Radio in Australia and New Zealand - Vol. I No. 02 - 18 April 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 02

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 2, 1923 — No. 3

(Start Graphic Description) SIX-YEAR-OLD RADIO ENTHUSIAST. (See page 63) — Underwood Photo (End Graphic Description)

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

P.49 - 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 2, 1923    Number 3

P.49 - Contents
CONTENTS.

 * Radiotorial . . . Page 51
 * Radio Entertainment . . . Page 52
 * Inductance, Capacity and Self Capacity of Coils . . . Page 53
 * How London "Listens-In" . . . Page 56
 * Australian Wireless Development . . . Page 57
 * Wireless Institute of Australia . . . Page 59
 * The Experimenters' Corner . . . Page 60
 * In Radio Land . . . Page 62
 * Call Letters . . . Page 66
 * Movements of Wireless Officers . . . Page 67
 * Low Power Tests . . . Page 68
 * Radiofun . . . Page 69
 * Club Notes and News . . . Page 70
 * Queries and Answers . . . Page 72

P.49 - 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.50 - Wireless Press Ad
(Start Photo Caption) (End Photo Caption)

P.51 - Radiotorial
Trans-Pacific Tests

T HE near approach of the Trans-Pacific radio tests directs attention to their importance to the wireless amateurs of .Australia. For some considerable time past a large number of enthusiastic experimenters all over .Australia have been hard at work building apparatus and completing arrangements in order that the best possible results may be achieved. It cannot be too strongly emphasised that these tests have a national as well as a world-wide interest. Therefore, it behoves all who have the progress of radio at heart to do all that lies in their power towards ensuring a large measure of success being recorded to the credit of .Australian experimenters. It can safely be assumed that those engaged in the actual task of attemptjng to receive the.messages transmitted by the .Amer ican amateurs will spare no effort to accomplish the aim they have in view. We trust that those not taking part in the tests will co-operate loyally with them to the rxtent of closing down their stations at the actual times at which it is calculated the messages will reach .Australia. lt is only a small sacrifice they are being asked to make, but non-compliance therewith will certainly have a very detrimental effect on the efforts of those who arc out to ,vin new distinctions for .Australian radio experimenters. There are some thousands of holders of receiving licensefl in the Commonwealth, and it naturally follows that each and every one is anxious to employ all his spare time in  listening in to the signals, music' and speech which, to a more or less extent, fills the air every night. It is these enthusiasts who are asked to call a halt while the tests are on in order that a clear field may be · allowed those who are seeking to establish a new long-distance record for low-power reception. The forthcoming test is easily the most important event that has yet engaged the attention of amateurs in .Australia. A wide appeal was made for entrants, and while the results, numerically comprise only a small percentage of those holding licenses, the standard. of the competitors is exceptionally high. This only emphasises the necessity of non-competitors allowing them a clear field. There is no means of ensuring this other than by appealing to the honour of 1those indirectly concerned in the success of amateur experimentation. "-~ ' We feel that once this fact is realisecl everv radio experimenter who possesses a valve rece'rving ;et will fall into line with · the wish of th Trans-Pacific 'l'est Committee and suspend his activities during the currency of the test. By doing so he will be acting in strict conformity with the high moral standard which has characterised the doings of radio experimenters iu .Australia, and incidentally rendering a distinct service to the cause of radio research.

Growth of Radio Clubs

THE grnclual formation of radio clubs throughout .Australia is a healthy sign. Less than twelve months ago the number in existence was considerably less than it is to-day, and almost every week we hear of new ones being formed. As might be expected, the growth has been much greater in and around the capital cities than in the country, but there is no reason ,Yhy the country districts of the various States should not have a large number of clubs, consistent with area and population, in the very near future. It must be obvious to anyone who cares to give the matter a moments consideration that the clubs are reallv stepping stones on which the great science of radio will rise to the same dominant position in .Australia that it occupies in America and England. That the public here are not yet educated to the valne and possibilities of wireless communication is not at all surprising. The average p erson regards radio as a subject far too complicated for his untechnical mind, and even when it is demonstrated that the science is simplicity itself to a person of ordinary intelligence he still remains more or less unconvinced. It is in cases like this that radio clubs are able to render valuable service. 'l'hc educational influence of a few lectures and demonstrations is beyond question, and the formation of a radio club: in any district is certain to arouse the interest of mai1y who would otherwise remain indifferent to the march of this truly wonderful science. For this reason, if no other, the growth of clubs is to be encouraged, and enthusiasts in country centres, no matter how small they may be numerically, should band themselves together for the advancement of their hobbv. The outback districts offer every facility for exp"erimentation, and a practical demonstration of transmitting and receiving messages between different towns will do more to arouse public interest than the most eloquent word picture of the possibilities of radio communication which it is possib'Je to pa.int. We hope to hear of the inauguration of many country radio clubs in the near future, and those who undertake to form them can rest aHsured that the work thev are doing will stand as a monurnent to their faith and ~nterprise long after radio has overstepped the limits which bound its horizon to-day.

P.52 - Wentworth Club's Successful Effort
'''Radio Entertainment. Wentworth Club's Successful Effort. Large and Appreciative Audience.'''

The members of the Wentworth Radio Club, which is presided over by Mr. Spencer Nolan, have every reason to feel elated at the success which attended their demonstration of wireless music at the Club rooms, Rose Bay, on the night of April 18. The committee went to considerable trouble to ensure success, and the whole-hearted appreciation of the large audience must have convinced them that the effort was well worth while. The first broadcast items to be picked up came from Mr. F. Basil-Cooke's up-to-date station at Clifton Gardens. Punctually at 7.30 p.m. Mr. Cooke commenced his experimental transmission, and for just on an hour the audience in the Club room at Rose Bay, as well as a large number who had gathered on the lawn outside, were delighted and entertained with the vocal and instrumental items which came in loud and clear.


text:
LMIs in Control/Click here to continue/Applications of Linear systems/Mixed H2-H∞ LMI Satellite Attitude Control

Satellite attitude control helps control the orientation of a satellite with respect to an inertial frame of reference mostly planets. In this section an LMI for Mixed $$H_2$$-$$H_{\infty}$$ Satellite Attitude Control is given.

The System
The system described below for Mixed H$$_2-$$$$H_\infty$$ Satellite Attitude Control is the same as the one used for separate $$H_2$$ and $$H_\infty$$ Satellite Attitude controls.

$$ \begin{align} &\quad \quad \begin{cases} I_x\ddot{\phi}+4(I_y-I_z)\omega _0^2 \phi + (I_y - I_z - I_z)\omega _0 \dot{\psi} = T_{cx} + T_{dx}\\ I_y\ddot{\theta}+3(I_x-I_z)\omega _0^2 \theta = T_{cy} + T_{dy}\\ I_z\ddot{\psi}+(I_x+I_z-I_y)\omega _0 \dot{\psi} = T_{cz} + T_{dz}\\ \end{cases} \end{align}$$

$$where$$

 * $$T_c$$ and $$T_d$$ are the flywheel torque and the disturbance torque respectively.
 * $$I_x$$, $$I_y$$, and $$I_z$$ are the diagonalized inertias from the inertia matrix $$I_b$$.
 * $$\omega_0= 7.292115 \times 10^{-5}rad/s$$ is the rotational angular velocity of the Earth, and $$\theta$$, $$\phi$$, and $$\psi$$ are the three Euler angles.

The state space representation of The Mixed $$H_2-H_\infty$$ Satellite Attitude Control system is given below, which is the same as the one described on the $$H_2$$ and $$H_\infty$$ Satellite Attitude Control pages.

$$ \begin{align} &\quad \quad \begin{cases} \dot x =Ax+B_1u+B_2 d \\ z_\infty=C_1x+D_1u+D_2d \\ z_2=C_2x \end{cases}\end{align} $$

$$where: $$

$$A = \begin{bmatrix} 0 & 0 & 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 0 & 1 & 0 \\               0 & 0 & 0 & 0 & 0 & 1 \\                \frac{-4\omega_0^2 I_{yz}}{I_x}  & 0 & 0 & 0 & 0 & \frac{-\omega_0 I_{yzx}}{I_x} \\ 0 & \frac{-3\omega_0^2 I_{xz}}{I_y} & 0 & 0 & 0 & 0 \\ 0 & 0 & \frac{-\omega_0^2 I_{yx}}{I_z} & \frac{\omega_0 I_{yzx}}{I_x} & 0 & 0 \end{bmatrix} $$

$$ B_1 = B_2 = \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \\                           0 & 0 & 0 \\                            \frac{1}{I_x} & 0 & 0 \\ 0 & \frac{1}{I_y} & 0 \\ 0 & 0 & \frac{1}{I_z} \\ \end{bmatrix}$$

$$C_1 = 10^{-3} \times \begin{bmatrix} -4\omega_0^2I_{yz} & 0 & 0 & 0 & -\omega_0 I_{yxz}\\ 0 & -3\omega_0^2 I_{xz} & 0 & 0 & 0 & 0\\ 0 & 0 & -\omega_0^2 I_{yx} & \omega_0 I_{yxz} & 0 & 0 \end{bmatrix}$$

$$C_2 = \begin{bmatrix} I_{3x3} & 0_{3x3} \end{bmatrix} $$

$$ D_1 = 10^{-3} \times L_1, D_2 = 10^{-3} \times L_2 $$

$$I_{ab} = I_a - I_b, I_{abc} = I_a - I_b - I_c $$

$$q = \begin{bmatrix} \phi \\ \theta \\ \psi \end{bmatrix},x = \begin{bmatrix} q & \dot q\end{bmatrix}^T, M = diag(I_x , I_y, I_z),$$ $$z_{\infty} = 10^{-3} M \ddot q ,$$ $$z_2 = q$$

These formulations are found in Duan, page 374-375, steps 12.10 to 12.15.

The Data
Data required for this LMI include moments of inertia of the satellite being controlled and the angular velocity of the earth. Any knowledge of the disturbance torques would also facilitate solution of the problem.

The Optimization Problem
There are two requirements of this problem:

 * Closed-loop poles are restricted to a desired LMI region
 * Where $$\mathbb{D} = \{s|s \in \mathbb{C}, L + sM + \bar{s}M^T < 0\}$$, L and M are matrices of correct dimensions and L is symmetric
 * Minimize the effect of disturbance d on output vectors z2 and zinf.

Design a state feedback control law

$$u = Kx$$

such that

 * 1) The closed-loop eigenvalues are located in $$\mathbb{D}$$,
 * 2) * $$ \lambda (A+BK) $$$$\subset \mathbb{D}$$
 * 3) That the H2 and Hinf performance conditions below are satisfied with a small $$\gamma_\infty  $$ and $$\gamma_2 $$:
 * 4) * $$\lVert G_{{z_\infty}d} \rVert_\infty = \lVert (C_1+N_2 K)(sI-(A+B_1K))^{-1}B_2+N_1 \rVert_\infty \leq\gamma_\infty$$
 * 5) * $$\lVert G_{{z_2}d} \rVert_2 = \lVert C_2(sI-(A+B_1 K))^{-1} B_2 \rVert_\infty \leq\gamma_2$$

The LMI: Mixed H2-H∞ Satellite Attitude Control
$$\begin{align} \begin{cases} &\text{min} \quad c_\infin \gamma_\infin + c_2\rho \\ &\text{s.t.} \quad \begin{bmatrix} -Z & C_2X \\ XC_2^T & -X \end{bmatrix} < 0 \\ \\ &\quad \quad trace(Z) < \rho \\ \\ &\quad \quad AX+B_1W + (AX+B_1W)^T + BB^T< 0 \\ \\ &\quad \quad L \otimes X + M\otimes (AX+B_1W) + M^T \otimes (AX+B_1W)^T < 0 \\ \\ &\quad \quad \begin{bmatrix} (AX+B_1W)^T +AX + B_1W & B_1 & (C_1X+D_2W)^T \\ B & -\gamma_\infin I & D_1^T \\ (C_1X+D_2W) & D_1 & -\gamma_\infin I \end{bmatrix} < 0 \\ \\ \end{cases} \\ \end{align}$$

Solving the above LMI gives the value of $$\gamma_\infin$$, $$\rho$$, and $$W, Z$$ and $$X > 0$$, where $$\rho$$ is equal to $$\gamma_2^2$$.

Conclusion
Once the solutions are calculated, the state feedback gain matrix can be constructed as $$K = WX^{-1}$$, and $$\gamma_2$$ = $$\sqrt{\rho}$$

Implementation
This LMI can be translated into MATLAB code that uses YALMIP and an LMI solver of choice such as MOSEK or CPLEX.

Related LMIs

 * H2 LMI for Satellite Attitude Control
 * Hinf LMI for Satellite Attitude Control


text:
LMIs in Control/Click here to continue/Applications of Linear systems/Mixed H2/Hinf LMI Satellite Attitude Control

The System
Using the same formulation of the problem as in the H2 and Hinf feedback applications (linked below) the system is of the form:

$$ \begin{align} I_x\ddot{\phi}+4(I_y-I_z)\omega _0^2 \phi + (I_y - I_z - I_z)\omega _0 \dot{\psi} &= T_{cx} + T_{dx}\\ I_y\ddot{\theta}+3(I_x-I_z)\omega _0^2 \theta &= T_{cy} + T_{dy}\\ I_z\ddot{\psi}+(I_x+I_z-I_y)\omega _0 \dot{\psi} &= T_{cz} + T_{dz}\\ \end{align}$$

This formulation comes from the process described in Duan, page 371-373, steps 12.1 to 12.8.

 * Tc and Td are the flywheel torque and the disturbance torque respectively.
 * Ix, Iy, and Iz are the diagonalized inertias from the inertia matrix Ib.
 * ω0 = 7.292115 x 10-5 rad/s is the rotational angular velocity of the Earth, and θ, Φ, and ψ are the three Euler angles.

The LMI below utilizes the state space representation of the above system, which is described on the H2 and Hinf pages as well:

$$\begin{cases} \dot x =Ax+B_1u+B_2 d \\ z_\infty=C_1x+D_1u+D_2d \\ z_2=C_2x\end{cases} $$

$$ \begin{align} A = \begin{bmatrix} 0 & 0 & 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 0 & 1 & 0 \\               0 & 0 & 0 & 0 & 0 & 1 \\                \frac{-4\omega_0^2 I_{yz}}{I_x}  & 0 & 0 & 0 & 0 & \frac{-\omega_0 I_{yzx}}{I_x} \\ 0 & \frac{-3\omega_0^2 I_{xz}}{I_y} & 0 & 0 & 0 & 0 \\ 0 & 0 & \frac{-\omega_0^2 I_{yx}}{I_z} & \frac{\omega_0 I_{yzx}}{I_x} & 0 & 0 \end{bmatrix}\\ \\ B_1 = B_2 = \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \\                           0 & 0 & 0 \\                            \frac{1}{I_x} & 0 & 0 \\ 0 & \frac{1}{I_y} & 0 \\ 0 & 0 & \frac{1}{I_z} \\ \end{bmatrix}\\ \\ C_1 = 10^{-3} \times \begin{bmatrix} -4\omega_0^2I_{yz} & 0 & 0 & 0 & -\omega_0 I_{yxz}\\ 0 & -3\omega_0^2 I_{xz} & 0 & 0 & 0 & 0\\ 0 & 0 & -\omega_0^2 I_{yx} & \omega_0 I_{yxz} & 0 & 0 \end{bmatrix}\\ \\ C_2 = \begin{bmatrix} I_{3x3} & 0_{3x3} \end{bmatrix} \\ \\ D_1 = 10^{-3} \times L_1, D_2 = 10^{-3} \times L_2 \end{align}$$

 * Iab = Ia - Ib, Iabc = Ia - Ib - Ic
 * $$q = \begin{bmatrix} \phi \\ \theta \\ \psi \end{bmatrix}$$, x = [q  q']T,   M = diag(Ix, Iy, Iz),     zinf = 10-3 M q ''' ,       z2 = q

These formulations are found in Duan, page 374-375, steps 12.10 to 12.15.

The Data
Data required for this problem include the moment of inertias and angular velocities of the system. Knowledge of expected disturbances d would be beneficial.

The Optimization Problem
There are two requirements of this problem:

 * Closed-loop poles are restricted to a desired LMI region
 * Where $$\mathbb{D} = \{s|s \in \mathbb{C}, L + sM + \bar{s}M^T < 0\}$$, L and M are matrices of correct dimensions and L is symmetric
 * Minimize the effect of disturbance d on output vectors z2 and zinf.

Design a state feedback control law

u = Kx

such that

 * 1) The closed-loop eigenvalues are located in $$\mathbb{D}$$,
 * 2) * λ(A+BK) $$\subset \mathbb{D}$$
 * 3) That the H2 and Hinf performance conditions below are satisfied with a small $$\gamma_\infty  $$ and $$\gamma_2 $$:
 * 4) * $$\lVert G_{{z_\infty}d} \rVert_\infty = \lVert (C_1+N_2 K)(sI-(A+B_1K))^{-1}B_2+N_1 \rVert_\infty \leq\gamma_\infty$$
 * 5) * $$\lVert G_{{z_2}d} \rVert_2 = \lVert C_2(sI-(A+B_1 K))^{-1} B_2 \rVert_\infty \leq\gamma_2$$

The LMI: Mixed H2/Hinf Feedback Control
min $$c_\infin \gamma_\infin + c_2\rho$$

s.t.

 * $$\begin{bmatrix} -Z & C_2X \\ XC_2^T & -X \end{bmatrix} < 0$$

 * trace(Z) < $$\rho$$

 * AX + B1W + (AX + B1W)T + BBT < 0

 * $$L \otimes X + M\otimes (AX+B_1W) + M^T \otimes (AX+B_1W)^T < 0$$
 * $$\begin{bmatrix} (AX+B_1W)^T +AX + B_1W & B_1 & (C_1X+D_2W)^T \\ B & -\gamma_\infin I & D_1^T \\ (C_1X+D_2W) & D_1 & -\gamma_\infin I \end{bmatrix} < 0$$

Gives a set of solutions to $$ \gamma_\infin, \rho$$, and W, Z and X > 0, where $$\rho$$ is equal to $$\gamma_2^2$$.

Conclusion
Once the solutions are calculated, the state feedback gain matrix can be constructed as K = WX-1, and $$\gamma_2$$ = $$\sqrt{\rho}$$

Implementation
This LMI can be translated into MATLAB code that uses YALMIP and an LMI solver of choice such as MOSEK or CPLEX.

Related LMIs

 * H2 LMI for Satellite Attitude Control
 * Hinf LMI for Satellite Attitude Control