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jan(at)claver.demon.co.uk
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 Posted: Thu Nov 26, 2015 6:13 am Post subject: Troubleshooting radio whine/noise on C essna 182P |
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Will be interesting to hear what the final outcome will be on your "noise" problem.
Regarding the isolation of the microphone - I am sure someone can give a better technical answer than I can. Simply put I think of the microphone circuit as being electrically insulated from chassis ground - hence you need too run two separate wires back to your radio. Think of it this way ... The microphone receives a steady signal on one wire - you speak into the mic - that changes the signal which now go back to the radio in the other wire ... 
The shield you have on the wire is to prevent any changes to the signal in the two wires ...
All the best
Jan
| Quote: | On Nov 26, 2015, at 01:38, sacha <uuccio(at)gmail.com> wrote:
Jan,
I think at this point I would agree with you: the problem is most likely related to the voltage regulator, not to switches.
I have ascertained that the noise is entering through the wires, not the antenna as its volume is independent of the radio volume.
I also tested the noise suppressor capacitor (cessna part 0770038-2) today with a multi-meter but I could not get it to give a reading so it may be fried. Although I just realized that I did not make sure it was discharged before I attempted to take the reading. I'll have to take that reading again. Nevertheless, the look of the part (an old rusty box), age of the plane (43yrs young) and the fact that I have seen capacitors fail in other equipment makes me think this might be a good candidate for replacement.
Regarding insulation of mic/headphone jacks, is it correct that mic jacks must be insulated from the airframe, but the headphone jacks may either be grounded to the airframe or insulated with a separate ground wire running back to the intercom? If it is correct, can someone explain the logic?
Happy Thanksgiving
Sacha
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sacha
Joined: 04 Jan 2015
Posts: 15
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| Posted: Sun Dec 06, 2015 10:17 am Post subject: Re: Troubleshooting radio whine/noise on C essna 182P |
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Thanks for your explanation about the radio grounding. It's obvious when one thinks about it.
I'm still struggling with this. I rechecked the capacitors and they measure 5.7 uF for the S1915 which is correct and 3.54 uF for the RFI filter (Cessna part 0770038-2) which seems like a plausible value.
So the only remaining possibility seems to be some bad connection somewhere, most likely on the ground side of things. But the puzzle remains as to why an alternator that fails can suddenly cause a grounding problem.
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