Intermittent squeal on both comms

[0TreeLemur]

Over the past six months or so my comm radios have developed an intermittent squeal when I transmit.   This happens independent from which radio I'm transmitting on.   At first I suspected the PTT switch, so I replaced that.  Negative effect.   Sometimes it is worse than other times.   Often I'll PTT and start talking, and after 1 or 2 seconds the squeal comes in.   Sometimes it happens immediately when I PTT without saying anything (now that's annoying).   I've had a couple of controllers mention it.

This happens independently from whether or not the other radio is on.   It happens when the radio I'm testing is the only thing switched on.  Seems unrelated to the intercom since controllers hear it.  Anybody dealt with this one?

Comm 1: KX155

Comm 2: GNS430W

 

[Baker Avionics]

47 minutes ago, 0TreeLemur said:

Over the past six months or so my comm radios have developed an intermittent squeal when I transmit.   This happens independent from which radio I'm transmitting on.   At first I suspected the PTT switch, so I replaced that.  Negative effect.   Sometimes it is worse than other times.   Often I'll PTT and start talking, and after 1 or 2 seconds the squeal comes in.   Sometimes it happens immediately when I PTT without saying anything (now that's annoying).   I've had a couple of controllers mention it.

This happens independently from whether or not the other radio is on.   It happens when the radio I'm testing is the only thing switched on.  Seems unrelated to the intercom since controllers hear it.  Anybody dealt with this one?

Comm 1: KX155

Comm 2: GNS430W

 

What intercom do you have and was there any maintenance done lately?  It seems that you have an issue with the mic jacks not being isolated from ground.  Now, that MAY not be the issue.  So, what intercom and/or Audio Panel do you have as well?  

[0TreeLemur]

 

2 hours ago, Baker Avionics said:

What intercom do you have and was there any maintenance done lately?  It seems that you have an issue with the mic jacks not being isolated from ground.  Now, that MAY not be the issue.  So, what intercom and/or Audio Panel do you have as well?  

Thanks for writing Greg.  I've got a sigtronics intercom and a Terra 230D audio panel.

You might be onto something here with mic jacks.   A couple of months ago I noticed that one of the back seat audio jacks had lost its capture nut.  I had to take the side panel out to fix it.  Maybe then I messed something up, with something on the mic jack side touching some part of the metal frame/steel tubing? 

[Baker Avionics]

16 hours ago, 0TreeLemur said:

 

Thanks for writing Greg.  I've got a sigtronics intercom and a Terra 230D audio panel.

You might be onto something here with mic jacks.   A couple of months ago I noticed that one of the back seat audio jacks had lost its capture nut.  I had to take the side panel out to fix it.  Maybe then I messed something up, with something on the mic jack side touching some part of the metal frame/steel tubing? 

Ok, there we go, possibly.  You need to be sure it has the black shoulder washer on one side of the mic jack and then a phenolic washer, the chrome washer and finally the hold down nut. 

See if this helps:

[Baker Avionics]

Here is an excerpt from the SPA400 Manual

 

[Baker Avionics]

@0TreeLemur if you need one of these washers, let me know and I will put one in the mail for you

[0TreeLemur]

Hi Greg, that's gotta be it.   Those parts must have fallen down into the gap between the seat and sidewall, and I just found a nut that fit and re-installed without any insulating washers.  I really appreciate your advice on this.  I'll PM you my info.  Thanks so much for your help. -Fred

[Baker Avionics]

12 minutes ago, 0TreeLemur said:

Hi Greg, that's gotta be it.   Those parts must have fallen down into the gap between the seat and sidewall, and I just found a nut that fit and re-installed without any insulating washers.  I really appreciate your advice on this.  I'll PM you my info.  Thanks so much for your help. -Fred

Replied Fred!  Also, I see that Oregon is not colored in on your maps above.  Hmmmm.....we need to fix that!  LOL.  I hope it is the issue and we are more than happy to help out!

[0TreeLemur]

3 minutes ago, Baker Avionics said:

Replied Fred!  Also, I see that Oregon is not colored in on your maps above.  Hmmmm.....we need to fix that!  LOL.  I hope it is the issue and we are more than happy to help out!

Yep, I'm planning  a great big loop next summer to fill in some of those states.  I'll definitely stop by for a visit when things get back to normal!

[Baker Avionics]

7 minutes ago, 0TreeLemur said:

Yep, I'm planning  a great big loop next summer to fill in some of those states.  I'll definitely stop by for a visit when things get back to normal!

Perfect!  We are right next to the fuel tanks at 3S8

[KLRDMD]

59 minutes ago, 0TreeLemur said:

Yep, I'm planning  a great big loop next summer to fill in some of those states.  I'll definitely stop by for a visit when things get back to normal!

Let me know when you come through AZ so I can see the old girl.

[0TreeLemur]

11 minutes ago, KLRDMD said:

Let me know when you come through AZ so I can see the old girl.

Will do!  I was recently contacted via LinkedIn by the gentleman who owned her from 1970-72.  He lives less than 45 Mooney minutes away in Georgia.  Once covid is over, I promised him a visit!   He's going to share photos with me when she was factory original "poppy red".

[aviatoreb]

Could it be something with your charging system?  Maybe your alternator protesting its getting old?  Or something with your voltage regulator getting old?

[0TreeLemur]

1 hour ago, aviatoreb said:

Could it be something with your charging system?  Maybe your alternator protesting its getting old?  Or something with your voltage regulator getting old?

I have a generator.  It weighs a ton but is very quiet. 

 @Baker Avionics nailed it I think.  I'll confirm this weekend.

[takair]

The grounds make sense.  I recently had a variation of this problem that got worse over time, mainly in transmit.  Had a buzz in the radios.  To my surprise it turned out to be the turn coordinator.  It is working fine, but I confirmed the electrical noise by unplugging it.  It had original Mooney wiring and the ground went to some location common to the audio ground.  The fix was to move the ground to an independent and remote location.  Audio and TC now in great working order.  Radio has never been so clear.

[0TreeLemur]

1 hour ago, takair said:

The grounds make sense.  I recently had a variation of this problem that got worse over time, mainly in transmit.  Had a buzz in the radios.  To my surprise it turned out to be the turn coordinator.  It is working fine, but I confirmed the electrical noise by unplugging it.  It had original Mooney wiring and the ground went to some location common to the audio ground.  The fix was to move the ground to an independent and remote location.  Audio and TC now in great working order.  Radio has never been so clear.

I did not know that ground proximity could have that affect.   Good to know, and I look forward to getting back to my non-squeal configuration. 

[takair]

23 minutes ago, 0TreeLemur said:

I did not know that ground proximity could have that affect.   Good to know, and I look forward to getting back to my non-squeal configuration. 

Yes, audio grounds and power are best isolated as much as possible from motors or other sources of electrical noise (thus the non conductive washers). When things are new, perhaps not as critical, but as motors age and the rotors start making some noise and the filters degrade...electrical noise (arcing is an extreme form)can make it into your very sensitive comm equipment and come through in the form of squealing, scratching, whining, and other noise.  Filters can help, but distance can be a free source of filtration.  Hope you get it sorted out.  Sometimes we don’t even realize how annoying they are until we get rid of them. 

[0TreeLemur]

On 11/26/2020 at 11:03 AM, takair said:

Yes, audio grounds and power are best isolated as much as possible from motors or other sources of electrical noise (thus the non conductive washers). When things are new, perhaps not as critical, but as motors age and the rotors start making some noise and the filters degrade...electrical noise (arcing is an extreme form)can make it into your very sensitive comm equipment and come through in the form of squealing, scratching, whining, and other noise.  Filters can help, but distance can be a free source of filtration.  Hope you get it sorted out.  Sometimes we don’t even realize how annoying they are until we get rid of them. 

Good day at the hangar today.  I re-assembled that mic jack correctly as per the figure provided by @Baker Avionics, using a temporary plastic washer, and the squeal is gone when I transmit!  Hurray!   THANKS GREG!

There is a whine coming through the system still that has been there for a long time.  Based on what takair said, I pulled the T&B CB and viola- the whine went away.  TCL ground confirmed loud-n-clear.   So it seems that my TC100 is making some noise, and something in the radio/intercom system is picking it up.   There is an A&P a Mooney hour away with an apprentice with skills in avionics.  I'll arrange to take it over to him.

-Fred

[carusoam]

Great pireps for the depth of knowledge of both @Baker Avionics and @takair

Thanks for sharing them...

Noises in the audio system are tough ones...

Best regards,

-a-

[0TreeLemur]

1 hour ago, carusoam said:

Great pireps for the depth of knowledge of both @Baker Avionics and @takair

Thanks for sharing them...

Noises in the audio system are tough ones...

Best regards,

-a-

Agreed!  I really appreciate benefiting from their experience!

[0TreeLemur]

On 11/26/2020 at 11:03 AM, takair said:

Yes, audio grounds and power are best isolated as much as possible from motors or other sources of electrical noise (thus the non conductive washers). When things are new, perhaps not as critical, but as motors age and the rotors start making some noise and the filters degrade...electrical noise (arcing is an extreme form)can make it into your very sensitive comm equipment and come through in the form of squealing, scratching, whining, and other noise.  Filters can help, but distance can be a free source of filtration.  Hope you get it sorted out.  Sometimes we don’t even realize how annoying they are until we get rid of them. 

Rob, doing some reading today I came across an interesting article on the Van's Air Force forum: https://vansairforce.com/community/showthread.php?p=972076

This article says that ideally if everything is grounded at one point on the airframe that this minimizes the potential for ground loops.  It also helps to minimize current flowing through the airframe and stray EM emissions.  This is counter to:

On 11/26/2020 at 9:15 AM, takair said:

The grounds make sense.  I recently had a variation of this problem that got worse over time, mainly in transmit.  Had a buzz in the radios.  To my surprise it turned out to be the turn coordinator.  It is working fine, but I confirmed the electrical noise by unplugging it.  It had original Mooney wiring and the ground went to some location common to the audio ground.  The fix was to move the ground to an independent and remote location.  Audio and TC now in great working order.  Radio has never been so clear.

Is this because the source of your noise was not a ground loop, but a stray emission from your TC ground wire?  Thanks.  Noob here on radio noise.

[takair]

11 minutes ago, 0TreeLemur said:

Rob, doing some reading today I came across an interesting article on the Van's Air Force forum: https://vansairforce.com/community/showthread.php?p=972076

This article says that ideally if everything is grounded at one point on the airframe that this minimizes the potential for ground loops.  It also helps to minimize current flowing through the airframe and stray EM emissions.  This is counter to:

Is this because the source of your noise was not a ground loop, but a stray emission from your TC ground wire?  Thanks.  Noob here on radio noise.

Great information there.  The noise is indeed what we would call conducted emission from the TC.  The TC motor is getting noisy, maybe even arcing.  Regarding the common grounds, the note from Ranier in the thread goes into more detail. Note how he lumps the systems into buckets.  Basically you want to keep the noisy grounds away from the sensitive equipment.......but you typically want to keep common system grounds together to avoid the ground loop.  So, Greg’s advice above was to minimize ground loops within the audio system.  My advice was to minimize noise on said grounds or unintentional ground loops.  Most airplanes are not assembled with the thought of electrical grounding.  We electrical types compete with our airframe engineer friends who want to prevent corrosion.  The coatings and wet assemblies are problematic for good ground planes.  A well designed airframe will have very specific ground clusters and power busses, based on equipment types.  This is one reason for an “avionics buss”. We go to great lengths to provide such power isolation, but not as much effort goes into the grounds.  Now, schematically, the power buss and the grounds appear to be the same, but for the reason above and as mentioned in the Vans thread, they are not always optimal.  Our Mooneys were designed when radios were an afterthought.  I guess when all you had was a speaker and no headsets, this noise was the least of their worries.  With today’s lower power and sensitive avionics, little things like ground and power placement, shielding, and even equipment qualification become critical.  When you see things qualified to DO-160x, part of it is it’s tolerance to other equipment or it’s ability to keep its emissions to themselves.  In the case of my TC, it likely would not pass today’s design standards....making it more important to improve my installation.  Hope this helps.  I work with folks who have Masters and PhDs just in these areas....so I am way over simplifying it.....mainly because that’s how I need to think about it...lol.  I’m glad they are around, because some of this can feel like black magic.

[0TreeLemur]

Thanks @takair.   A couple of years ago I bought a spare TC100 that is relatively new.   It was refurbed in 2011.   I could swap the one in my plane with it, which I'm pretty sure hasn't been opened up in decades.  Sadly, when it arrived someone had cut the shielded cable between the TC and the inverter.   That will be a challenge for someone to repair, I suppose.   Maybe that's worth looking into.  

Anybody know what the inverter on the TC100 does?  Does it output A/C power?

FWIW the noise in my headset when the TC is running is probably about in the 2-5 kHz range.   It doesn't change as the TC spins up.   The instant I push in on the TC CB the noise appears.   The instant I pull the CB, the noise stops.

[takair]

19 minutes ago, 0TreeLemur said:

Thanks @takair.   A couple of years ago I bought a spare TC100 that is relatively new.   It was refurbed in 2011.   I could swap the one in my plane with it, which I'm pretty sure hasn't been opened up in decades.  Sadly, when it arrived someone had cut the shielded cable between the TC and the inverter.   That will be a challenge for someone to repair, I suppose.   Maybe that's worth looking into.  

Anybody know what the inverter on the TC100 does?  Does it output A/C power?

FWIW the noise in my headset when the TC is running is probably about in the 2-5 kHz range.   It doesn't change as the TC spins up.   The instant I push in on the TC CB the noise appears.   The instant I pull the CB, the noise stops.

From one of the manuals I have, the wires should be color coded and there are techniques to repair the braid.  Do you have a picture, feel free to PM or email...may be able to help.  As for the noise, I would look for the ground wire off of the inverter and see where it goes.  I suspect the TC100 may be noisier than some.

[0TreeLemur]

1 minute ago, takair said:

From one of the manuals I have, the wires should be color coded and there are techniques to repair the braid.  Do you have a picture, feel free to PM or email...may be able to help.  As for the noise, I would look for the ground wire off of the inverter and see where it goes.  I suspect the TC100 may be noisier than some.

I looked and the inverter is grounded on a lug right below the pilot-side control column shaft, on a screw that penetrates the steel tubing.   There are about three other things grounded there too.  Here's a photo of the really nice looking TC100 with the sliced wire.   Why they did this blows me away.