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Bill Bradburry wrote:
Ernest,
I have a plastic plane and everything grounds at the same forest of tabs place per Sir Nuckolls. :>)
Everything? As in EVERY-thing?
That's kinda my point. The forest of tabs is a strip of metal with a measurable resistance. People will ground the alternator at one end, and then run a wire to the battery negative post from the other end. An oscilloscope in the middle of the forest will show all sorts of waveforms in the audible range. The same goes for a forest of tabs for the positive side of the equation.
Pull all of the audio stuff off and give it its own forest to play in. Allow for one positive and one negative lead over to the main busses. Some of those nasty waveforms will still make it over, but at that point all of the audio stuff will be riding the same wave and you won't hear it.
Bill B
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*From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] *On Behalf Of *Ernest Christley
*Sent:* Sunday, July 10, 2011 9:34 PM
*To:* Rotary motors in aircraft
*Subject:* [FlyRotary] Re: Noise in headset when I turn the alternator on
On 07/09/2011 10:16 AM, Bill Bradburry wrote:
This is not a big problem since I can not hear the hum when in flight, but I thought someone might be able to tell me how to stop it. I have the Renesis and I am using the stock capacitor that is attached to the engine. When I turn on the alternator, there is a slight buzzing hum that appears in the headset and the frequency goes up and down with the engine. It is pretty obviously the alternator I think.
Does anyone have any suggestions?
Bill B
How do you have your audio system grounded, Bill. People make ground loops more complicated than it really is. If you'll just keep in mind that every wire is also a very tiny resistor, I think most of the misconfigured grounds would solve themselves. I think what I've seen a lot of is people will ground there radio at point A, and the intercom at point B. Electrons from the charging system (or any other noisy system like strobes) have to pass through A and B to get to the battery (the ultimate source AND destination of all electrons in the system). Because the conductor between A and B is a resistor, a small but very real voltage is created. Because the audio system is designed to work off of very small voltage, you can hear every change in the A-B voltage.
The solution is simple. Don't allow ANYTHING to route its electrons between the ground points of all the audio equipment. Bring all the audio grounds to a single point and then that single point to a good ground with a single wire. I actually made a separate circuit board to connect all the audio stuff. Everything comes to jumpers on that one board, and there is a single ground line. I tested my audio equipment last week with the engine going strong. Not a single bit of noise. Well, at least not electrical noise. There was LOTS of exhaust noise. 8*)
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