'So you think that you have a RFI problem ?'



T
oday it can be a challenge to obtain clear reception of HF signals.
This plagues Ham radio operators as well as shortwave listeners alike.

At my old apartment the RFI levels were extreme to say the least.
No internal antenna could pick up anything but noise and even simple outdoor wire antennas were equally poor performers.

Things seemed pretty bleak until I started experimenting with small loop antennas.

The loop antenna in this demonstration video was approximately 5 meters (1/10 Wavelength) in circumference.
The main loop was actually part of the aluminum window frame.

To connect to the main loop a much smaller pickup loop , called a ''Faraday loop'', was made from coaxial cable.
It was 1/5 of a diameter of the main loop and was similar to this design.




The pickup loop was placed near to the window frame loop.
Typically with small loops like this (aka magnetic loop) you would use a variable capacitor to resonate the main antenna loop.
As my main loop was the window frame adding a capacitor was not possible , nevertheless it was still found to be acceptable for receiving purposes in the upper SW HF bands , but as expected it did suffer below 5MHz.
To improve performance lower in the frequency range the main loop would have to have been bigger in size.




When completed this antenna provided a vastly superior signal to random wire antennas , even though it was much smaller in size.
This is because loop antennas like this are not sensitive to near field signals.

As much of the noise that we hear is generated close by to our listening location most types of antennas that are close to it will pick it up strongly , drowning out the comparatively weak radio signals.
As loop antennas are essentially deaf to near RF sources the signals from further out are now heard.

In the example video below it shows me switching from the
window frame loop antenna to the random wire antenna of about 10 meters in length which goes outside up into a tree.
The loop is connected to the Lo-Z coaxial connection and the random wire is connected to the Hi-Z spring terminals.
A slide switch on the rear of the radio selects between the two.


Click the image below to see the short video.

https://www.youtube.com/watch?v=HiI2agS6AiE


Or Download the video in AVI

Remember , It starts off with the loop connected and then ends with the random wire antenna.





As you can see , the difference between the two antennas is like night and day.

RFI problems don't need to end radio listening pleasure , but sometimes you have to work outside the box to achieve worthwhile results.
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https://www.youtube.com/user/HamAndShortwaveRadio