A loop antenna is actually sensitive to the magnetic field and not the electric
field (it is also called a magnetic loop).
They form other antenna types, which feature simplicity, low cost and versatility. You l'll find loop in various shapes; square, circle, triangular, etc.
Widely used up to 3 GHz..electrically small C<0.1 lambda , electrically large C~lambda. Broadcast AM .
tube or transistor) radios are usually equipped with ferrite loop antennas.
Such Magnetic Loop antennas are widely used in WIFI antennas too.
A bit of theory.
Know how to solve Maxwell equations ,Gauss' law for electricity and magnetism?
Or geet you prefer ready-made calculation programs?
There are several ways to build and calculate your Magnetic Loop. A lot of information is available on the net, concerning Magnetic and other
type of Loop Antennas.
Good books about Magnetic Loops are,
The ARRL antenna book Chapter 5 tabel 3.
The Rothammel Antennabook.
A lot of theory and design is described, about magnetic fields,
Magnetic Loops,Shielded loop antennas, formula's etc.
Also the importance of direction finding antenna's (handy for searching QRM / man make noise near your QTH).
The best way to begin is:
Make several small Magnetic Loops, for example 2 meter or 70 cm. Using 6mm thick copper oil pipe Then if you have enough experience WICU pipe ( 12/15/22mm or thicker).
This is made from a soft red copper material and easy to bend, and to process.
To measure de resonance frequency from the Magnetic Loop. take a look at: YouTube for a introduction movie, how to use the MFJ 259(B).
- Easy to build
- Good RX (High Q)
- Reduction of man make noise
- Small size, handy in small gardens .
- Small bandwidth
- Dangerous high voltage on the capacitor ( 100 watt = 3 Kv ).
- Strong magnetic field, keep distance by high power 100 watt or more.
λ = Wavelenght in meters
f = Frequency in MHz.
c = Speed of light, in kilometer p/sec ( 10³ )
φ = Circumference in meters
D =Loop diameter, in meters
λ = c / f
λ = 300 / 3.604
λ = 83.24084351
L = λ / 4
L = 20.81021088
D = l / φ
D = 6.627455693
The circuference = 7 meter.
Wavelenght λ = 300 / 3.604 = 83 meter
¼ λ = 83 / 4 = 20.81 meter
Loop diameter = 20.75 / 3.14 = 6.62 / 3.14 = 2.10 meter.
calculation: pg9hf (c)2012.