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Noise on headsets induced by strobes


NicoN

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As long as I am part of co-ownership for this M20K, we have "chirp" - noise on both headsets as long as the strobes are switched on.

It is not very loud, but it is there.

Recently, two of the power supplies have been repaired and all strobe are flashing now. When re-assembling, I took special care of grounding the power supply and also connecting the shield for the 12V power-line correctly to ground. It was pretty corroded.

Nevertheless the "chirp" is still there, not more as before but still the same. And even more, now we have a second "chirp" beacuse the power supply in the tail has no connection for sync. Only the two nin the wings are synced.

So, for the 12V power a shielded cable is used and the shield is grounded. But for the sync-line there is not a shielded wire! ( seems not be important as the aft one has no sync!).

Are there any ideas around how to get rid of this "chirp" ?

Throwing away the high-voltage strobes and moving to LED is not an option for the next year, I guess

Edited by NicoN
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9 minutes ago, NicoN said:

As long as I am part of co-ownership for this M20K, we have "chirp" - noise on both headsets as long as the strobes are switched on.

It is not very loud, but it is there.

Recently, two of the power supplies have been repaired and all strobe are flashing now. When re-assembling, I took special care of grounding the power supply and also connecting the shield for the 12V power-line correctly to ground. It was pretty corroded.

Nevertheless the "chirp" is still there, not more as before but still the same. And even more, now we have a second "chirp" beacuse the power supply in the tail has no connection for sync. Only the two nin the wings are synced.

So, for the 12V power a shielded cable is used and the shield is grounded. But for the sync-line there is not a shielded wire! ( seems not be important as the aft one has no sync!).

Are there any ideas around how to get rid of this "chirp" ?

Throwing away the high-voltage strobes and moving to LED is not an option for the next year, I guess

Every mooney I’ve flown in (sample size 6) including a relatively new ovation, that didn’t have LED’s has had a chirp when the strobes are on.  Not saying that’s right... just that’s been my experience.

edit- I tend to mitigate the strobe chirp by adjusting my volumes on the audio panel so I don’t really notice it any more.

Edited by M016576
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I am not familiar with the sync lines are connected, or not, on the various models. Just throwing out ideas on how you can pinpoint the source of interference.

Another thought is to run the strobes on a separate power source to see if interference is through the power lead.

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Sorry for the late answer. The Audio Panel is an KMA24.

WHat do you mean with "ground the power supplies at the battery"?

The minus-line of each power supply is shortly connected to the air frame. The battery minus shoud do the same.

 

Another idea: from my experience with repairing the power supplies, I learnt that the sync wire should also have a pretty high voltage on it, but it is non-shielded :-(

Also, it seems funny to me, that the cable from the power supply to the strobe-light itself is NOT shielded. It is a distance of about 2 or 3 feet and there is definitely high voltage on it!

Has anybody tried shielding the "last 3 feet" of the cable?

 

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25 minutes ago, NicoN said:

Sorry for the late answer. The Audio Panel is an KMA24.

WHat do you mean with "ground the power supplies at the battery"?

The minus-line of each power supply is shortly connected to the air frame. The battery minus shoud do the same.

 

Another idea: from my experience with repairing the power supplies, I learnt that the sync wire should also have a pretty high voltage on it, but it is non-shielded :-(

Also, it seems funny to me, that the cable from the power supply to the strobe-light itself is NOT shielded. It is a distance of about 2 or 3 feet and there is definitely high voltage on it!

Has anybody tried shielding the "last 3 feet" of the cable?

 

Another thing to look at is whether or not your headsets are grounded properly. I had an issue with "ground loops" that allowed my headset jacks to act as antenna. Once I got the proper insulators in place, the noise went away. The headsets should be grounded through the audio panel.

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1 hour ago, NicoN said:

Sorry for the late answer. The Audio Panel is an KMA24.

WHat do you mean with "ground the power supplies at the battery"?

The minus-line of each power supply is shortly connected to the air frame. The battery minus shoud do the same.

 

Another idea: from my experience with repairing the power supplies, I learnt that the sync wire should also have a pretty high voltage on it, but it is non-shielded :-(

Also, it seems funny to me, that the cable from the power supply to the strobe-light itself is NOT shielded. It is a distance of about 2 or 3 feet and there is definitely high voltage on it!

Has anybody tried shielding the "last 3 feet" of the cable?

I thought I remember reading somewhere that the sync wire was a low voltage signal, but I might be wrong on that

I do remember reading that the current to the strobe power supplies was actually pretty constant, since it is continuously charging the capacitors between each flash.  If anything, LED flashers would be more prone to noise from the power cable, since their current comes on and off.

I have non-LED strobes on the wings (my tail strobe has been out since I've owned it), but I've never had problems with noise from the strobes.  Of course, I usually have the volume on my headset turned down all the way and the volume up on the radios to minimize noise (if you have to turn the volume on your headset up, you're amplifying noise as well).

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1 hour ago, NicoN said:

 

WHat do you mean with "ground the power supplies at the battery"?

The minus-line of each power supply is shortly connected to the air frame. The battery minus should do the same.

 

I think I found the assumption that one poster (Greg) was trying to eliminate...

For most real electrical circuits in vehicles... grounding to the airframe should work...

Unfortunately, some circuits cause noise in other circuits and simply grounding to the airframe doesn’t work as well as expected...

Relying on the airframe to do the grounding job is not the best for a few things...

Certain circuits are are more sensitive to noise.  Some circuits are more noisy.

A reminder to also check grounding strap health in their various locations as well.

 

Examples of sensitive... Audio, video, and engine data wires...

Examples of Noisey... Ignition wires, electric motor wires, strobe wires...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

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28 minutes ago, carusoam said:

I think I found the assumption that one poster (Greg) was trying to eliminate...

For most real electrical circuits in vehicles... grounding to the airframe should work...

Unfortunately, some circuits cause noise in other circuits and simply grounding to the airframe doesn’t work as well as expected...

Relying on the airframe to do the grounding job is not the best for a few things...

Also, aircraft aluminum is a worse conductor than steel, and some of the coatings used can make chassis grounding more susceptible to ground loops, I think

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Nico,

Expect a few things may have changed in 40 years...

1) Ground straps may have been lost, or broken, or their connections corroded....

2) Some things can be grounded better than the original design... both the noise makers, and the audio sensitive devices....

3) My first experience with this came in my M20C... the motorized red light could be heard humming along through the ancient audio system...

Good luck with the hunt!

Best regards,

-a-

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  • 2 weeks later...

Seems, it will be a real adventure!

 

BTW: Reading the wire-scheme for my Sigtronics Intercom:

  • Only the MIC-Jacks should/must be isolated from airframe-ground to a single point ground., while the headset-jacks seem to have their own ground to airframe.

Just one more question: Avoiding ground loops means to have all the jacks collected to ONE single point and THEN connected to airframe or to something else?

Simply asking: WHat will I measure when I use my Ohmmeter between the Jacks housing and airframe, supposed the jack is correctly isolated ? High Resistance? Or low resisnatnc, because it is still connected to airframe ( at ONE point).?

 

 

Merry christmas!

 

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Nico- it should be 0 ohms (or very close to 0) resistance since you are just measuring a path from one point to the other connected by the airframe (basically the equivalent of a straight run of wire).

The reason for the common ground is simply to cut down on the amount of background noise the microphone circuits pick up from strobes, alternator, etc.

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4 hours ago, NicoN said:

Seems, it will be a real adventure!

 

BTW: Reading the wire-scheme for my Sigtronics Intercom:

  • Only the MIC-Jacks should/must be isolated from airframe-ground to a single point ground., while the headset-jacks seem to have their own ground to airframe.

Just one more question: Avoiding ground loops means to have all the jacks collected to ONE single point and THEN connected to airframe or to something else?

Simply asking: WHat will I measure when I use my Ohmmeter between the Jacks housing and airframe, supposed the jack is correctly isolated ? High Resistance? Or low resisnatnc, because it is still connected to airframe ( at ONE point).?

 

 

Merry christmas!

 

IIRC, the jack grounds come from the radio, and the shielding is grounded to the radio as well.  The radio itself should be wired properly to the avionics (or main bus) ground bar, and that should be properly wired to the battery and attached to the airframe as well.

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Seems, it will be a real adventure!
 
BTW: Reading the wire-scheme for my Sigtronics Intercom:
  • Only the MIC-Jacks should/must be isolated from airframe-ground to a single point ground., while the headset-jacks seem to have their own ground to airframe.
Just one more question: Avoiding ground loops means to have all the jacks collected to ONE single point and THEN connected to airframe or to something else?
Simply asking: WHat will I measure when I use my Ohmmeter between the Jacks housing and airframe, supposed the jack is correctly isolated ? High Resistance? Or low resisnatnc, because it is still connected to airframe ( at ONE point).?
 
 
Merry christmas!
 


The only way you can check to see if your jacks are truly isolated is to remove the ground from the audio panel and check the jack against the plane. It should read wide open. If you are seeing any continuity, you are either shorted or have a ground somewhere.

Make sure you use good isolating washers on the jacks. All of my noise issues were caused by the jacks grounding on the mounting plate.


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The factory used non-shielded wire and grounded the power supplies at the end of the wing.   Because of this a lot of electrical noise gets into the structure of the aircraft and then find its way into the radio bus. Either via the 12v power line that goes into bus or the ground. If you pull three conductor shielded wire to each strobe power supply and then one of those goes to the +12v off of the switch the other you connect with the sync  wire and the third tie  this together into a single shielded wire to the negative battery post that will do wonders for your noise. 

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