ron228rj(at)gmail.com
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 Posted: Wed Jun 27, 2018 8:58 pm Post subject: Mysterious Solution to Radio Noise |
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I recently started flying with a new Garmin GTR-200 radio. My antenna design and placement is new and highly experimental. I made a full wave loop from 22 AWG and installed it one foot in front of my instrument panel. Since the fuselage circumference is too small there, it is more of a zigzag loop.
Initial results are good. I transmitted from 10 miles away from the airport and the Unicom reported loud and clear. When low on final, I heard a radio transmission from and airport 70 miles away. And, I had no problem talking to ATC in the DC SFRA.
BUT, on many frequencies I get continuous noise on the radio. Increasing the squelch configuration didn’t help. I noticed that when I changed screens on my GRT Sport EX EFIS the noise changed its character. And, sure enough, with the EFIS off, the continuous noise goes away. I did discover that the back of the case of my EFIS is not grounded like everything else on the panel. But, connecting ground to it didn’t change anything.
However, the noise completely goes away if I just touch the radio or radio rack with my finger. The radio case and rack are both grounded. I checked that. So, I grabbed a two foot length of 22 AWG wire and taped one end to the radio rack and connected the other end to nothing. The result was the same as when I touched it. The noise is gone and the radio works normally.
So, there’s the fix, but how and why does it work?
Thanks,
Ron
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