Becker AR-4201 Design Fault?

Well, I was wrong. The Becker AR4201 radio that’s in my current glider is not generating noise internally on 123.50 MHz. The noise is coming from a GPS in the glider.

In my first glider, I heard noise on 123.50 MHz from the AR4201. The noise was only on that frequency, though, and I sold that glider before I got around to tracking down the source of the noise.

In my second glider, when I heard noise again on 123.50 MHz from its AR4201, I removed the radio from the glider and connected it only to an antenna and a speaker. I heard noise on 123.50 MHz with the antenna disconnected, so I knew it had to be coming from inside the radio. Naturally I figured that the AR4201 had been the source of the noise I'd heard in my first glider, too.

In my third glider, when I also heard noise on 123.50 MHz from its AR4201, I pulled all the fuses except for the radio. The noise was still there, so I believed it was again inside the radio. Strike 3 against Becker? No. Crucially, I had not disconnected the antenna. Yesterday I did disconnect the antenna and surprise, surprise, there was no noise. I obviously goofed during my previous trouble shooting on this glider! But what was the problem?

While reconnecting the antenna, I noticed a green blinking LED on my Cambridge GPS 25. What the heck? It turned out some genius at the factory had wired the GPS 25 to power without going through the panel fuses! When I unplugged the power lead from the GPS 25, the radio became noise free on 123.50 MHz with the antenna connected. Time for ferrites on the GPS 25, and time to exonerate Becker...

Thanks to everyone who wrote in on this thread. I appreciate your helping me to find the source of my noise problem.

-John, Q3

Glad you found the issue and resolved it (sorta).
Thanks for the follow-up, may help others down the road!

The way I like to trouble shoot a radio that is breaking squelch is to turn on only the radio with no squelch.......wide open, so that it gives all background noise. Then I turn on all other electrical equipment, one at a time. Think of it as filling a dam, noise from each unit adds to the overall water level. When the dam is full it spills over or breaks squelch. All equipment will add a little background noise, but some add tremendous amounts. The Cambridge GPS is about the worst offender I have run across. You can try moving the GPS as far away from radio antenna as possible, do this with radio on as you listen to the background noise in different positions. Best bet may be to get another GPS. Grounding everything to ships ground may help, shielding and ferrit's may also help.
Good luck,
JJ

JJ, That's a good technique for finding noise generators, thanks for sharing. You know the glider, so you'll remember that the GPS is on the parcel shelf. That means the radio antenna cable and the GPS output run together for almost 10 feet. I was always going to replace the L-Nav and Gps-Nav, that may happen sooner now.

-John, Q3

On Friday, July 22, 2016 at 6:34:05 PM UTC-4, wrote:
The way I like to trouble shoot a radio that is breaking squelch is to turn on only the radio with no squelch.......wide open, so that it gives all background noise. Then I turn on all other electrical equipment, one at a time. Think of it as filling a dam, noise from each unit adds to the overall water level. When the dam is full it spills over or breaks squelch. All equipment will add a little background noise, but some add tremendous amounts.. The Cambridge GPS is about the worst offender I have run across. You can try moving the GPS as far away from radio antenna as possible, do this with radio on as you listen to the background noise in different positions. Best bet may be to get another GPS. Grounding everything to ships ground may help, shielding and ferrit's may also help.
Good luck,
JJ