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?
Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Alternator static
- Thread starter bob888
- Start date
Carl Froehlich
Well Known Member
New problem or always there?
Carl
Carl
ALT NOICE
As it seems related to both alternators, I would check engine ground to
firewall and negative bus bar. It is important that the connection is good.
Also check that the headset female plugs (LO) in the panel are not connected
to air-frame GND.
A poor grounding of the antenna (corrosion) may also present problems.
Good luck
As it seems related to both alternators, I would check engine ground to
firewall and negative bus bar. It is important that the connection is good.
Also check that the headset female plugs (LO) in the panel are not connected
to air-frame GND.
A poor grounding of the antenna (corrosion) may also present problems.
Good luck
I would start with the antenna wiring and connectors. The engine puts out many undesirable EMI signals. However, a properly functioning radio and antenna can deal with them, but a system with faults cannot. The fact that you are only getting this on a few frequencies means that it is an issue with the radio or it's antenna. If it were noise floating around via your grounds it would likely appear more universally. Not saying that ground noise isn't getting to the radio or antenna, but things like noise on power bus and frame ground bus tend to first appear all the time on the headsets, not just on a radio and only on a few frequencies. If the issue was between the radio and the audio panel or anywhere out to the headsets, the static would be present on ALL frequencies.
The very first thing I would check was resistance from the antenna's base plate airframe ground, as this one of the more likely issues to just pop up. next is to check continuity of both center conductor and ground from one side of cable to the other. Be sure to wiggle everything around while testing. And next is to test the antenna. A simpler check is to plug a rubber antenna from a handheld into the radio and see if the problem disappears. if it does, you know the radio is good and your issue is somewhere in the antenna or it's wiring.
The fact that you can make the noise go away by turning off the alternator does not necessarily mean that the alternator is the problem. If it were, it is very likely that the noise would be far more problematic.
The very first thing I would check was resistance from the antenna's base plate airframe ground, as this one of the more likely issues to just pop up. next is to check continuity of both center conductor and ground from one side of cable to the other. Be sure to wiggle everything around while testing. And next is to test the antenna. A simpler check is to plug a rubber antenna from a handheld into the radio and see if the problem disappears. if it does, you know the radio is good and your issue is somewhere in the antenna or it's wiring.
The fact that you can make the noise go away by turning off the alternator does not necessarily mean that the alternator is the problem. If it were, it is very likely that the noise would be far more problematic.
Last edited:
Carl Froehlich
Well Known Member
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
