RFI causes radio to break squelch (TKM MX300)

[mtuomi]

Ok, I have no idea if I'm using the correct terminology, but I have a very intermittent issue with my radio (confirmed with the same radio on another airplane so not installation related I believe).

When I fly over areas where I expect to have plenty of radio interference (such as masts, antennas and so on), my radio will think someone is transmitting and I can hear noise. If someone does transmit, it is not affected at all and I can hear them clearly and they can hear me. But the squelch thinks someone is transmitting all the time.
It's so intermittent that I don't want to pay $500 to TKM or Bevan-Rabell to repair it, but I was wondering what part could cause that issue.

 

[bnt83]

Ok, I have no idea if I'm using the correct terminology, but I have a very intermittent issue with my radio (confirmed with the same radio on another airplane so not installation related I believe).

When I fly over areas where I expect to have plenty of radio interference (such as masts, antennas and so on), my radio will think someone is transmitting and I can hear noise. If someone does transmit, it is not affected at all and I can hear them clearly and they can hear me. But the squelch thinks someone is transmitting all the time.
It's so intermittent that I don't want to pay $500 to TKM or Bevan-Rabell to repair it, but I was wondering what part could cause that issue.

https://www.pilotsofamerica.com/community/threads/garmin-430w-problem.97174/#post-2114282

 

[mtuomi]

Thanks, I'll try that when this rainy mess moves out. Symptoms are identical.

Just to make sure I read it correctly - only repair is a new ELT?

 

[Pat Elliott]

but I have a very intermittent issue with my radio (confirmed with the same radio on another airplane so not installation related I believe).

if it did the same thing in another airplane, it's not your ELT, From the TKM manual...

III. OPERATING THE MX300

Operating controls for the MX300 are located on the front panel or through three access
holes in the rear panel. Through the rear panel, adjustments for modulation percentage,
side tone, and speakers can be made (see figure 1). Newer units will also have a squelch
adjustment accessible through a hole in the top cover.

 

[weirdjim]

if it did the same thing in another airplane, it's not your ELT, From the TKM manual...

And you know this how?

Jim

 

[mtuomi]

Both planes were C150M's, I'm assuming he has same AmeriKing ELT as I do (as most C150's do).

 

[weirdjim]

Both planes were C150M's, I'm assuming he has same AmeriKing ELT as I do (as most C150's do).

Sorry, I wasn't aware it was you with the problem.

Jim

 

[Pat Elliott]

And you know this how?

Jim

Well, you are correct, I don't know, BUT if the problem follows the radio, I would suspect the radio. Guess I should have asked more questions such as are the airframes the same, equipped the same? etc.

 

[weirdjim]

Well, you are correct, I don't know, BUT if the problem follows the radio, I would suspect the radio. Guess I should have asked more questions such as are the airframes the same, equipped the same? etc.

The problem with the varactor-mixing in the output transistor C-B junction is that the tuning is affected by minute differences in the length of the antenna, the length of the coax between the antenna and the ELT ... and the like. Identical radios, identical airframes, and identical ELTs aren't necessarily electrically identical.

JIm