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Q-talk 87 - Build a Simple Radio-Checker

Build this simple loop pickup, plug it into your tape recorder, and do your own "radio-check". The pickup loop will work across the complete aircraft band. So the frequency you transmit does not matter.

There are times when no one is around to give you a radio check and sometimes you would like to hear how you actually sound on the radio yourself. Well, now you can

Take a 14-inch length of #20 insulated hookup wire and strip both ends about 1/4-inch Get an 1/8-inch two-conductor plug (RS-274-286), some 1N33A germanium diodes (RS-276-1123), and a .01 MFD ceramic capacitor (RS-272-131).

Solder one end of the 1N34A diode to the center conductor of the plug and the other end of the diode to one end of the 14-inch wire. Now solder the other end of the wire to the longer, outside conductor of the plug. Solder the .01 MFD capacitor to both the center and longer, outside conductor of the plug. Insulate as needed with electrical tape or other similar methods like heat shrink.

To use this pickup loop, plug it into the microphone input of your tape recorder. Hold the loop flat against a side window of your airplane or lay it on the seat. Press the Record button and then transmit a test message using your aircraft radio. Press Stop, rewind and play back your recorded message to hear exactly how you sound on your radio.

I used a GE micro cassette recorder Model 3-5376A. I am sure many other tape recorders will work as well. Most tape recorders use 1/8-inch plugs. Some inexpensive tape recorders are not very sensitive, but I think this loop will still provide a good signal. I put the cathode of the 1N34A (the banded end) to the shorter center pin of the 1/8-inch plug, but either way should work. If it seems the tape recorder is getting too much of a signal, try holding the loop 90-degrees to the window or distort the round loop into a narrow ellipse. You can also build a smaller loop, if you wish. I tested my loop with a handheld transceiver about two feet away from the recorder. Remember, the position of the loop with respect to the radio antenna determines the strength of the signal picked up. Sitting in the cockpit, the radio transmitter signal is usually strong enough that the loop orientation is not too important.

Once you have determined a good test spot for your loop and airplane, you will be able to notice if your radio begins to sound unusual or if microphone A is clearer than micro

phone B. I use "Loop flat against window test message" or "Loop flat on copilot seat test message" or "Microphone A test message" so that I will know what I am listening to when I play it back. Listening to yourself like this will help you learn to make clearer transmissions. You can use the "automatic voice-activated record" feature and tape-record an entire flight if you wish. Since the loop is not tuned, it will pickup your transmissions anywhere in the aircraft band. Good luck.


Radio Shack Part Number

1/8" Plug


1N34A Diode


.01 MFD Capacitor


#20 Insulated Wire

14 inches

You can order a printed copy of Q-talk #87 by using the Q-talk Back Issue Order Page.