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madriver42(at)gmail.com
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 Posted: Mon Nov 29, 2010 8:51 am Post subject: Radio noise |
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I know this has been discussed before but like to ask anyway. I installed an old RST 360 com radio in my 701 panel and when I start the "Rotax" it is very noisy. Seems to be a whine don't know whether or not this is alternator or ignition. Saw a wiring diagram for another radio which stated that you must install a 22,000uf capacitor in series on the 12v feed when used with the Rotax engine installation. Will this cure the problem? Your valued thoughts please.
Phil Smith
CH 701 - Flying
Buhl, ID
[quote][b]
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psm(at)att.net
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| Posted: Mon Nov 29, 2010 9:25 am Post subject: Radio noise |
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Hi Phil,
If you put a capacitor in series with your power feed to anything it will stop working - any capacitor blocks Direct Current and passes some amount of Alternating Current. If you want to filter the 12V power you must connect the capacitor between the 12V line and the return line or ground. If you want to try this I would recommend a much smaller capacitor to start - perhaps 50 or 100 microfarads. These are small ceramic (disks?) available at Radio Shack for about the price of the blister package. If you install one near the radio it might help reduce radio frequency noise going to the radio power supply. Still, I don't think this is your problem.
I don't have personal experience with this problem, but I have been reading comments about it for years. The usual solution is to work on the ground path between your headset and radio. It requires a good shielded ground path directly to the radio to work properly. This is usually accomplished by using coaxial cable for the circuit between the radio and headset in both the microphone and earphone paths. This solution works on the principle that it is the audio circuit that picks up the noise rather than the power supply to the radio.
If that doesn't solve your problem I would suggest working on the ground path to your radio from the battery. I have a large copper braid in my plane for this purpose. It runs all the way from the battery negative terminal to the instrument panel. This helps the power supply in the radio do its job.
Good luck,
Paul
Camas, WA
XL installing upgrade
From: owner-zenith-list-server(at)matronics.com [mailto:owner-zenith-list-server(at)matronics.com] On Behalf Of Philip Smith
Sent: Monday, November 29, 2010 8:47 AM
To: aeroelectric-list(at)matronics.com; 701801-list(at)matronics.com; zenith-list(at)matronics.com
Subject: Radio noise
I know this has been discussed before but like to ask anyway. I installed an old RST 360 com radio in my 701 panel and when I start the "Rotax" it is very noisy. Seems to be a whine don't know whether or not this is alternator or ignition. Saw a wiring diagram for another radio which stated that you must install a 22,000uf capacitor in series on the 12v feed when used with the Rotax engine installation. Will this cure the problem? Your valued thoughts please.
Phil Smith
CH 701 - Flying
Buhl, ID
01234567890123456
[quote][b]
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davgray(at)sbcglobal.net
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| Posted: Mon Nov 29, 2010 10:27 am Post subject: Radio noise |
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Phil
I had a similar problem with my XCom. To find it I Started pulling fuses one by one to test for any circuit that may be causing the problem.
When I got to the accessory power circuit to the rear of the aircraft it stopped.
My headset wiring was shielded over the entire length except the last 2 inches. Interference got in at the distal 2 inches where it was unshielded and ran too close to a small linear switching voltage regulator output wires.
Another problem was the intercom squelch not set high enough which caused an unbearable
interference at take off power even though my headset was the only one plugged in.
The large capacitor is used across the charging circuit to filter the dynamo output as it enters the battery bus. Check out the
Aeroelectric.com site for the details and correct capacitor.
Gary Ray
From: Philip Smith (madriver42(at)gmail.com)
Sent: Monday, November 29, 2010 11:47 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com) ; 701801-list(at)matronics.com (701801-list(at)matronics.com) ; zenith-list(at)matronics.com (zenith-list(at)matronics.com)
Subject: Radio noise
I know this has been discussed before but like to ask anyway. I installed an old RST 360 com radio in my 701 panel and when I start the "Rotax" it is very noisy. Seems to be a whine don't know whether or not this is alternator or ignition. Saw a wiring diagram for another radio which stated that you must install a 22,000uf capacitor in series on the 12v feed when used with the Rotax engine installation. Will this cure the problem? Your valued thoughts please.
Phil Smith
CH 701 - Flying
Buhl, ID
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flyadive(at)gmail.com
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| Posted: Mon Nov 29, 2010 10:27 am Post subject: Radio noise |
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Phil:
A WHINE is an ALTERNATOR issue.
If you had a rough hashing sound then it would be ignition.
In either case the sound should increase in frequency as the engine increased in speed (RPM).
The 22,000 uF capacitor (or larger 33,000 or 50,000 uF (at) 16WVDC) goes IN PARALLEL with the B+ wire coming from your Alternator. Got that? NOT in series.
It goes from the B+ terminal (the Positive side of the Capacitor) - To GROUND / GND (the Negative side of the Capacitor). ---| (--- The side to the left is the Positive.
Let me know if you understand what I'm saying.
As far as curring the problem.... I don't know, I have ONLY your expiation of the problem go diagnose by.
Barry
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