On Friday, July 15, 2016 at 1:19:23 AM UTC-7, bumper wrote:
On Wednesday, July 13, 2016 at 7:03:39 AM UTC-7, John Carlyle wrote:
JJ, I haven't tried that experiment yet. Need to find a 50 ohm terminator and then get out to the airport where the glider is stored. I'll post the results.


You wouldn't need a 50 ohm terminator (dummy load) if you don't transmit. You are only seeing if the interference is RF, coming into the radio via antenna or coax. Disconnecting the coax at the back of the radio should do. If that does eliminate the noise, then a hand held radio with squelch turned down might be useful in locating source.

If it does not eliminate the interference when powered from aircraft buss, turn other stuff off one by one to try to find guilty device. Install ferrites on wiring. If it's still present when powered up from a battery (no other devices turned on) then for sure it's internal.

LNAV would generate a lot of noise and break squelch on some frequencies. Ferrites on LNAV wiring solved problem for me. Best if there's enough wiring slack to go through the ferrite hole more than once - though once will often do.

bumper

The terminator is necessary to keep the radio from receiving anything on the antenna input. An unterminated input will function as a poor antenna. You can make a terminator with a BNC cable and a 50 ohm resistor soldered between the center conductor and the shield. Or you can buy one at:

http://www.trianglecables.com/produc...WMCRoC5vrw_wcB

This is the only way to resolve the issue presented.

Tom