I have plane power internally regulated alternator and a B&C standby alternator on the vacuum pump pad, externally regulated. On certain frequencies I get loud static, like broken squelch. It happens with either alternator running but quiets completely if I turn off the alternators. I'm not sure where to look since it occurs with either alternator. Ideas?
Not sure what conclusions can be made from this. But - I’ll guess:
- At first blush, both alternators are showing the same noise (whenever either is on and the other off). Not likely that both have an issue so need to look for a common cause. Perhaps if you further detail the conditions of the noise going away (as in what you change) this assumption can be verified or ruled out.
- The noise seems to be voltage dependent as it is only there when an alternator is on. This could point to another component in the plane as the root issue.
- While I can see some other component as a noise source, I would not guess “antenna ground” as the cause. As I’ve posted before, RF ground and DC ground are two very different things.
So, now time to roundup the usual suspects:
- You are looking for something that is generating RFI and the RFI changes with buss voltage.
- Verify the noise is not present when on the ground with the engine off.
- Connect a regulated power supply (not a battery charger) to the battery and raise buss voltage to you normal value with the engine running. Noise come back?
- Open all breakers (other than the radio and audio panel). Noise gone? Shut one breaker at a time and log results.
LED lighting is a typical RFI source, There are ways to mitigate this problem. As this problem is new (I’m assuming no changes made) then look for wiring issue. Here how you ground the LED lighting power lead shielded wire would be the first on the list.
And the sleeper issue is a USB charger port. Isolate it.
As you have not reported any engine cranking problem it is safe to assume engine ground is adequate.
Have fun,
Carl