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New alternator
Not an expert here but you mention that you got a new alternator - did you have this problem with the old alternator? Was anything else 'new' or 'changed' just before the problem started?
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Good question. The alternator is new, and was installed with the engine. Unfortunately, there is no before to compare to.
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Troubleshooting update
I finally got around to trying out all the suggestions you guys have provided.
First I disconnected everything electrical except intercom, radio, engine display, alternator, mags, and still had the noise, so I think it isn't RFI from any of the periferal circuits. Then I tried the ferrite beads with no effect. Then I disconnected the radio and the intercom from the aircraft system and used an additional battery to run them. I tried all three combinations, radio on the battery, intercom on the battery, and both on the battery. I still got the noise every time the radio was powered up, didn't seem to matter from where. The wires between radio and intercom and the wires to the headset jacks are all shielded. It is an older radio, a Terra 760D. So my thought is that the radio unit itself is picking up the RFI. Any thoughts out there for where to go next? |
Back in the day...this used to be a big problem on Cessna and ADF sine the alt noise would kill the ADF from pointing. The answer was always a bad capacitor on the alternator. Not that far along on my build so I am not sure what is standard today or if it is built in to the alt these days. Maybe someone else can chime in with further details
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Disconnect the antenna from the radio (DON'T TRANSMIT!!) and see if the noise is coming thru. Evidently this is a case of radiated EMI. Also how well is your engine grounded?
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Check your grounds.
Do you have a single point aivionics grounding point? Is the case/tray of the radio grounded? |
I have tried disconnecting the antenna without effect.
I have checked all the grounds, I don't have a dedicated ground strap for the radio rack, it should be grounded through the brackets. But would the problem be ground issues if I still get the RFI with the radio completely disconnected from aircraft power and running on a separate battery? |
I fixed mine.
I had the same noise in my 6. When I added power the whine increased in pitch. The more things I put on the louder the noise. Though I had an alternator problem. What I did was to bring the alternator power output to a fuse buss on the firewall, and connected to the load side of the main contactor. I used to have it in the cockpit under a circuit breaker on the panel. I also did the common ground setup as Bob Nuckolls suggests. All loads are brought back to the firewall mounted ground strap, inside the cockpit and under the cowl. My plane is now dead quite in the headsets, under all conditions. Where is your alternator power lead connected to the battery?
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