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Alternator Noise When Touching Metal Airframe Grounds

 
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nuckolls.bob(at)aeroelect
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PostPosted: Sun Jun 10, 2018 8:37 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

At 09:21 PM 6/9/2018, you wrote:
Quote:
I've always had various levels of alternator and strobe noise in my audio system, and have never been able to track down and eliminate the problem. Today I was flying lots of short hops in the warm weather, sweating more than usual, and I noticed an interesting clue.

The noise got much louder when I touched the metal part of the push/pull throttle control. So then I tried the mixture, and prop controls, same thing. Then I tried the ceiling-mounted aluminum elevator trim wheel (which doesn't connect to the engine, of course), same thing. Touching the screws that hold the instrument panel in place, or the aluminum air vent in the panel did not generate the noise.

I'm not really sure where the circuit path is in this case. The headset only makes contact with me through insulators like the leather ear seal covers and the furry pad at the top. My shoes have rubber soles, and seat upholstery is the only other thing I'm in contact with.

Has anyone encountered this before, and figured out what was causing it? It almost reminds me of being able to make noise by pointing my fingers near the heated windshield of some old plane I flew once. Sort of a windshield theremin

Have you run the traps on seeking to discover
at what point noise is entering the system?
What volume controls or switches have an
effect on the noise you hear? What does
your audio system look like? Stereo phones?



Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Jun 12, 2018 11:27 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

At 08:44 PM 6/11/2018, you wrote:
Quote:
Thanks for your help Bob. It's a 4-place airplane with stereo panel-powered Lemo jacks, parallel two-plug jacks (all isolated from the airframe) and a PS Engineering PAR100EX audio panel/intercom. In the past I've played with the volume controls but didn't think to try it out on this most recent flight. In the past, the noise was reduced when I turned down the intercom volume level, or the local headset level on the Bose X.

Okay, the fact that intercom volume has
an effect suggests that the noise is getting
in upstream of the intercom. The "touch
sensitivity" is suggestive of a possible
poor or even floating ground in the
upstream wiring.

Downloaded the manual . . . do you have
the remotely controlled comm transceiver?





Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Jun 12, 2018 2:12 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

At 03:01 PM 6/12/2018, you wrote:
Quote:
Yes, and also a gns430w and skyview system.

Just for grins . . . try unplugging the
data cable between the intercom/controll
panel and the remote transceiver . . . and
see if the noise is affected.



Bob . . .


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PostPosted: Tue Jun 12, 2018 2:13 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

At 03:01 PM 6/12/2018, you wrote:
Quote:
Yes, and also a gns430w and skyview system.

Just for grins . . . try unplugging the
data cable between the intercom/controll
panel and the remote transceiver . . . and
see if the noise is affected.

Oh yeah, are you sure it's alternator whine . . .
pitch rises and falls with engine rpm?



Bob . . .


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PostPosted: Wed Jun 13, 2018 3:32 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

At 03:31 PM 6/13/2018, you wrote:
Quote:
Thanks Bob, I'll try that early next week and report back. What I was calling alternator noise does rise and fall with engine RPM, and goes away when I pull the main alternator field CB

very well . . . just making sure we're
peering into the right rabbit hole . . .



Bob . . .


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PostPosted: Mon Jun 18, 2018 12:51 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

At 02:16 PM 6/18/2018, you wrote:
Quote:
Thanks Bob and everyone, I'm back with new data, having returned to the airplane and flown it today.

Disregard what I said before about the volume- the noise is not impacted by the local headset volume or by the intercom volume, or the 430 volume. It seems to be not adjustable at all. It does not seem to be present when the engine is not running, but then again the alternator noise is the majority of the noise, and it would not be present with the engine off.

Are these headsets noise canceling? I.e. fitted with
electronics of some kind? I was looking for Bose X
Model info on the 'net with no success for the quick
look-see.



Bob . . .


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PostPosted: Tue Jun 19, 2018 5:03 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

At 07:37 AM 6/19/2018, you wrote:
Quote:
Yes, ANR heAdsets powered by the airplane electrical system.

Okay, do I correctly interpret that your
audio system is capable of using either
the Bose X or say a plain vanilla headset?

The fact that your noise is affected by
changes in body conduction suggests that the
stimulus is entering the system through
those spaces in close proximity to your
bod . . . like the things clamped on your
head?

Try another headset if you can . . .



Bob . . .


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PostPosted: Tue Jun 19, 2018 10:07 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

At 09:36 AM 6/19/2018, you wrote:
Quote:
Good suggestion, thanks. So far all 4 lemo sets are the same. I have a dual plug version of the same bose to try, and can do that and report back

Hmmmm . . . not sure I've got an accurate image
of the differences between 'lemo' and 'dual plug'.
Does this described the connectors at the end
of the headset cord . . . single mulit-pin as opposed
to "Y" plugs?

To be significant, the test headset needs to
be a generic, non-electronic . . . but go
ahead and try the dual-plug Bose X too.



Bob . . .


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