Intermittent Squelch Problem

danhagan

danhagan

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El Paso, TX
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danhagan
Radio stack is:

1. Comm1 - Garmin 530
2. Comm2 - Bendix King KX 155
3. AudioPanel - PSA 6000

Problem: I hear over-powering squelch on the ground or when over-flying within 1300 feet AGL (especially if radio towers around). It is intermittent. I have shutdown each of the above components individually and totally including running the Garmin 530 in "fail safe" and still get it. It sounds like you pulled your squelch knob. It occurs on both Comm1 and Comm2. It seems to improve at altitude. It doesn't matter how long the radios have been on - although it seems worse at the beginning after engine start. I have shutdown EVERYTHING on board trying to isolate the problem.

Not performed: Saw a suggestion I think from weirdJim in another thread to check before engine start (didn't do this).

Hangar buddy suggested it was probably the ELT picking up interference and he suggested disconnecting it and flying it (haven't as I figured something would have to be listed inop or placarded). ELT is the older type and not the 406. Suggestions?
 
danhagan said:
Radio stack is:

1. Comm1 - Garmin 530
2. Comm2 - Bendix King KX 155
3. AudioPanel - PSA 6000

Problem: I hear over-powering squelch on the ground or when over-flying within 1300 feet AGL (especially if radio towers around). It is intermittent. I have shutdown each of the above components individually and totally including running the Garmin 530 in "fail safe" and still get it. It sounds like you pulled your squelch knob. It occurs on both Comm1 and Comm2. It seems to improve at altitude. It doesn't matter how long the radios have been on - although it seems worse at the beginning after engine start. I have shutdown EVERYTHING on board trying to isolate the problem.

Not performed: Saw a suggestion I think from weirdJim in another thread to check before engine start (didn't do this).

Hangar buddy suggested it was probably the ELT picking up interference and he suggested disconnecting it and flying it (haven't as I figured something would have to be listed inop or placarded). ELT is the older type and not the 406. Suggestions?
Click to expand...


Your buddy is probably right. I've experienced the same symptoms and then test flew with the ELT removed and the symptoms disappeared.

ELT's can be removed for 90 days following the instruction in FAR 91.207.

Somehow older ELT's pickup the radio trash from high powered transmitters, it mixes with the circuits in the ELT and gets reflected out the ELT which the com and/or nav radios pickup.
 
Last edited:
bnt83 said:
Somehow older ELT's pickup the radio trash from high powered transmitters, it mixes with the circuits in the ELT and gets reflected out the ELT which the com and/or nav radios pickup.
Click to expand...

It took us the LONGEST time to figure this one out. Turns out the collector-base diode in the output transistor acts as a parametric oscillator/mixer due to variations in Cob and turns out trash all over the band when whapped hard enough by really high powered (or highly directional antennas) FM stations. You could never track it down because some FM stations on different frequencies would generate the trash in the aircraft band and others would generate it in some other band.

You are correct; you can operate the aircraft up to 90 days without an ELT, put it back in for 5 minutes, take it out again ... or just say to hell with it and if ever called on the carpet, "...but I just took it out yesterday...".

Don't forget to put it back in a few days before the annual.

Jim
 
weirdjim said:
It took us the LONGEST time to figure this one out. Turns out the collector-base diode in the output transistor acts as a parametric oscillator/mixer due to variations in Cob and turns out trash all over the band when whapped hard enough by really high powered (or highly directional antennas) FM stations. You could never track it down because some FM stations on different frequencies would generate the trash in the aircraft band and others would generate it in some other band.

You are correct; you can operate the aircraft up to 90 days without an ELT, put it back in for 5 minutes, take it out again ... or just say to hell with it and if ever called on the carpet, "...but I just took it out yesterday...".

Don't forget to put it back in a few days before the annual.

Jim
Click to expand...

Didn't get an opportunity to try removing the ELT until this weekend. Unfortunately, it does not appear to be the ELT causing the intermittent squelch to kick in ... ELT is already back on board.

Ran into my old mechanic and he questioned a new alternator we had to replace last year ... I told him I had the problem prior to the new alternator.
 
I had this issue. Turns out my problem was the usb adapter plugged into the cigarette lighter. I've tried various ones but they all seem pretty noisy.
 
Another thing to check is that the remote control panel for the ELT may have a dying battery. That causes many of them to go goofy. They do not have a sane fail safe mode.
 
focal_plane said:
I had this issue. Turns out my problem was the usb adapter plugged into the cigarette lighter. I've tried various ones but they all seem pretty noisy.
Click to expand...

Haven't been using one in mine, so can't be that ...

flyingron said:
Another thing to check is that the remote control panel for the ELT may have a dying battery. That causes many of them to go goofy. They do not have a sane fail safe mode.
Click to expand...

Will look into that next Ron, thanks ...
 
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