Weak transmission/noisy intercom

[Morgan3820]

With the annual complete I had some money left over So I went to my friendly avionics shop to have him replace my gs/loc, vor cdi's. One man shop, older gentleman doing this for 40 years, nice guy. He talked me into a new audio panel (while I have it all torn apart...). Immediately started having radio issues, nothing big at first. Not picking up ATC reliably, like they were not hearing me. When I asked my home tower they described my transmissions as poor. Checked my transmission with a handheld and it sounded fine to me. So, went up for some pattern work, static was coming through on Com1, switched to Com2, static went away. Tower complained about weak transmissions, switched back to Comm1, still bad. Landed, went to local mechanic, got him in the plane on headset, started engine....NO static, radio check to ground control..loud and clear. Don't you just hate it when you can't reproduce the fault for the mechanic. Pull out the plane the next day..static on Comm1 again! Clear on Comm2. Shove plane, gently, back into hangar.

1. Static whether engine is running or not. I hear the strobe beacon pop through the static. When I turn off beacon, popping stops but static remains. Never hear the strobe pop before.
2. Weak transmission on both coms, both navs appear to function fine.
3. Intermittent but appears to be getting worse and more frequent.
4. Static does not change pitch with engine speed but I first noticed the problem at idle RPMs. Now at all RPMs.
5. Static comes through both headset jacks. Intercom seems to work fine as I can talk to my passenger and he to me.
6. Digital EGT/CHT takes 20 minutes to turn on, but stays on thereafter and reads expected temps. Maybe related to cold.

Avionics guy suggested one of the magnetos, but would not the engine need to be running for the mags to be the cause. And the runup was normel. I cycled the alternator switch with no change and amp meter is steady and showing a charge.

I have a trip planned in two weeks but I will not go if this issue is not resolved. Please help me go on my trip.

Thank you in advance.

 

[bluerooster]

Shielding on one or more wires not properly connected.

 

[Morgan3820]

Shielding on one or more wires not properly connected.

I was thinking along those lines, but the problem is getting worse. Wouldn't bad shielding make it bad from the first and stay constantly bad?

 

[weirdjim]

With the annual complete I had some money left over So I went to my friendly avionics shop to have him replace my gs/loc, vor cdi's. One man shop, older gentleman doing this for 40 years, nice guy. He talked me into a new audio panel (while I have it all torn apart...).

Does your ISP charge you by the character? If not, what do you mean by replacing the GS/LOC and VOR CDIs? What "new" audio panel did you get?

Jim
.
.

 

[Morgan3820]

Does your ISP charge you by the character? If not, what do you mean by replacing the GS/LOC and VOR CDIs? What "new" audio panel did you get?

Jim
.
.

I had a KI-214, 201 and I changed them out for used KI-209, 208.
PMA 6000 is the new audio panel.

 

[Chip Sylverne]

Are your antenna coaxes bundled inside the harness with the power wiring, or broken out and bundled separately? Maybe there's some rf interference because of how the harness is bundled.
Even with shielded wire, stranger things have happened.

 

[Mikejr718]

Take a look at the antenna coax cables. Look for splices with bnc connectors. The outside of the bnc connector is a direct path to the sheilding inside the antenna coax. If the bnc connector is against something with a different potential to ground than the cable end ground it can cause problems. Specifically if the bnc connector can vibrate around in flight. alternately making contact and not contacting. Possibly wires and cables where disturbed unintentionally while work was done behind the panel. Had a similar problem in my Citabria.

 

[mscheuer]

Dear Reno,

You wrote

1. Static whether engine is running or not. I hear the strobe beacon pop through the static. When I turn off beacon, popping stops but static remains. Never hear the strobe pop before.
2. Weak transmission on both coms, both navs appear to function fine.
3. Intermittent but appears to be getting worse and more frequent.
4. Static does not change pitch with engine speed but I first noticed the problem at idle RPMs. Now at all RPMs.
5. Static comes through both headset jacks. Intercom seems to work fine as I can talk to my passenger and he to me.
6. Digital EGT/CHT takes 20 minutes to turn on, but stays on thereafter and reads expected temps. Maybe related to......

Thank you in advance.

Here is my input:


1. Static whether engine is running or not. I hear the strobe beacon pop through the static. When I turn off beacon, popping stops but static remains. Never hear the strobe pop before.

This is most likely a ground loop issue. Please make sure that all mic and headphone jacks are isolated from ground by insulation washers. If you don't see them, they have to be installed

2. Weak transmission on both coms, both navs appear to function fine.

Not the audio panel! During radio transmissions, we mechanically connect (through relays) the headset to the selected radio

3. Intermittent but appears to be getting worse and more frequent.

Don't have any input on this

4. Static does not change pitch with engine speed but I first noticed the problem at idle RPMs. Now at all RPMs.

To determine if some of this noise is coming from the music input, listen carefully to the noise and then blow into them IC, if the noise goes away but slowly returns after you cease to trip the VOX open, some noise is coming from the music input. Again either ground loops noise or conducted.

5. Static comes through both headset jacks. Intercom seems to work fine as I can talk to my passenger and he to me.

Not the intercom

6. Digital EGT/CHT takes 20 minutes to turn on, but stays on thereafter and reads expected temps. Maybe related to cold.

Not the intercom.

Thank you for purchasing our audio panel, we will be happy to help in any fashion we can.

Sincerely,

Mark Scheuer
PS Engineering, Inc.

Avionics guy suggested one of the magnetos, but would not the engine need to be running for the mags to be the cause. And the runup was normel. I cycled the alternator switch with no change and amp meter is steady and showing a charge.

I have a trip planned in two weeks but I will not go if this issue is not resolved. Please help me go on my trip.

Thank you in advance.

 

[Stewartb]

PS Engineering continues to impress. Mark gave me a similar diagnostic summary after my newly built Cub had a hot mic that had us scratching our heads. Above and beyond typical customer service. Bravo, sir.

 

[Morgan3820]

Thanks to all. Returning to the installer tomorrow to troubleshoot. Hopefully a resolution.