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jan(at)CLAVER.DEMON.CO.UK
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 Posted: Tue Nov 24, 2015 11:15 am Post subject: Troubleshooting radio whine/noise on C essna 182P |
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My money is on the regulator for the noise ... I do not think changing the
master switch will solve your noise problem ... Prove it by just shorting
out the switch !.. Or temporary mount any old 'toggle switch' to just prove
the point ....
--
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sacha
Joined: 04 Jan 2015
Posts: 15
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| Posted: Wed Nov 25, 2015 5:38 pm Post subject: Re: Troubleshooting radio whine/noise on C essna 182P |
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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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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Thu Nov 26, 2015 6:47 am Post subject: Re: Troubleshooting radio whine/noise on C essna 182P |
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The microphone jack should definitely not be grounded locally to the airframe, because other varying current (noise) through the airframe will get amplified along with the microphone signal. It is good practice not to ground the headphone jack either.
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sacha
Joined: 04 Jan 2015
Posts: 15
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| Posted: Wed Dec 02, 2015 11:06 am Post subject: Re: Troubleshooting radio whine/noise on C essna 182P |
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I took some measurements of bus voltage using a Bluetooth oscilloscope called a Mooshimeter. Here are 3 graphs. I'm also including a fourth one which is picture of the voltage in my car cigar lighter for comparison.
Two things are noticeable:
1. The amplitude of the ripple in the aircraft is smaller by a factor of 3 or 4.
2. There seem to be higher frequency components in the aircraft than in the car.
Does anyone have any thoughts about this?
I'm thinking that maybe the noise suppression capacitor is fried and I'd like to test this hypothesis without shelling out $125 for the Cessna part. Can anyone suggest a sensible capacitor I could try out?
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