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MAGNETIC LOOP ANTENNA By G4TUG

Below is the result of my own research and practical findings of my Magnetic Loop Antenna.

There are quite a lot of designs for both small loop antennae (less than 0.8 of a wavelength) and large antennae (more than 1 full wavelength). Both types are usually used for direction finding purposes. The foregoing are almost all electrostatic loops. However, an exception is the shielded loop that actually blocks out the electrostatic component. I feel sure we all know that aerials emit electrostatic and electromagnetic fields.

Many discussions and debates have taken place over the air and in clubs about the magnetic loop properties and usage; resolving this is the purpose of my short note about my findings.

Some say that the mag. loop is directional and others say not. Both are correct. It is not significantly directional for sky waves but is so on ground wave and that gives it a superb means of vastly reducing unwanted emissions.

Looking from above (plan view) the mag.loop has a figure-of-eight polarisation. Many people attempt to peak up the wanted signal but without any worthwhile success. The reason is because the lobes are so broad. The proper method of use is to null out the unwanted interfering signal because the null points are a very sharp knife edge indeed, being at right angle to the lobes. The unwanted signal could be from a welding garage, hospital, industrial estate, beacon etc.; almost anything emitting a ground wave. It does not matter from which direction the sky wave is coming; it will probably not be affected at all.

The mag.loop is a very high Q device thus giving excellent frequency rejection away from the wanted (and tuned) signal.

Some other advantages are:

That it is designed to operate between approximately five and ten feet from the ground. Raising it any higher would not improve performance at all, probably detract. My own is mounted atop my clothes line pole.

It may be mounted among trees and other objects. It should not be closer than ten feet from metal structures though. It is not necessary to use it in the loft unless it will not fit elsewhere.

I trust the above will clarify and enlighten, dispelling some of the misconceptions that I have heard.


Rod, G4TUG 

g4tug@talktalk.net


LINKS TO G4TUG SUBJECTS
About Me (index) Ham Radio Cars
Hobbies RodLog Ham Radio Logging System Software Reading
My Diet Magnetic Loop Antenna Sailing
Computers Noise Figure of Receivers and Pre-amps Gardening
Links to other sites Experimental HF All Band Aerial Classic Films