What I found is that it can sometime be linked to a ground loop. One way to get around this is to have a better ground. Try this, disconnect your ground wire and run a large grounding wire from your radio directly to your battery’s ground. Run-up your engine and see if the noise is still there. My guess is that it will be gone, and you will know that you have a bad ground.
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De : Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] De la part de David Leonard
Envoyé : 9 juillet 2011 18:44
À : Rotary motors in aircraft
Objet : [FlyRotary] Re: Noise in headset when I turn the alternator on
On Sat, Jul 9, 2011 at 7:16 AM, Bill Bradburry <bbradburry@bellsouth.net> 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
That is a really common and difficult problem. I still have an alternator buzz. I fly a certified Navion that has a buzz worse than mine. Almost all aircraft have it to some extent. Here are some things to look into and try.
Besides the alternator, look into contributing sources. For me, it is an interaction between the alternator and the intercom. Turn off either device, and the buzz goes away. So if I am solo, I can turn off the intercom. For me, the buzz through the intercom is only weakly dependent on intercom volume. So I can turn down the volume on the headsets and up the volume on everything else, and it minimizes the buss.
I also got small improvements from each of the following:
Installing an noise choke on the power supply to the intercom.
Moving the power supply for the alternator field off the main buss (that included the avionics) into an engine compartment buss near the main alternator power out.
Using shielded wire for the entire run of the alternator field wire. (to the switch and back).
But then better than that, I installed a relay near the alternator so that the field power only travels a short distance and the only connection to the alternator switch is the trigger for the relay. That also improved an alternator over-voltage issue.