Ham Radio

Passive Field Strength Meter

building a Passive Field Strength Meter


Since I moved to my new QTH I’m in a constant search for an antenna.
I can’t put dipole or vertical so I did some research and settled on Magnetic Loop antenna.

The next few month will be dedicated to the build of this antenna.

I found Kevin’s (KB9RLW) channel on YouTube (here) and he got many videos about Magnetic Loop.
One of them is about junk box magnetic loop, it’s fascinating to see how it performs so well.

In the middle of the video he explains how to build a passive field strength meter (RF meter) so I wanted to give it a try.


I ordered the needle meter from eBay and the rest I found in my drawer so I don’t have values and part numbers.

1x Needle Meter 0-50μA (I think it’s called 44C2)
2x Germanium Diodes
1x 10k or more Potentiometer
Few wires



The build is fairly easy as you can see on the schematic I draw.
If you connect it and the needle is moving to the left, you need to reverse the polarity of the diodes.

In the end I tested it with my UHF radio on my local AllStar node and it worked just fine.

I think It’ll sit in my controlling box for the Magnetic Loop.

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