Popping static navcom

[JMichael]

What do you make of this? Popping static that is random, but occurs at a higher frequency in flight. It is not heard when a transmission is being received. It is not heard on a handheld. It is heard on both left and right seat ports. There is no audio panel. Michel radio in a Stinson. Both mags were recently rebuilt and it has a tailbeacon ADS-B out. Aircraft does not have static wicks and I'm in an area that tends to have high humidity.

 

[Bell206]

What do you make of this?

When did you 1st notice the static? After the mag work or any other work?

Define “random”?

Is there a beacon or strobe light installed?

Are you sure you can’t duplicate it on the ground?

 

[JMichael]

Random means no periodicity. However, I suppose that a plot of engine firing events against popping events might show a correlation where a random pop coincides with an engine firing, although I don't have the equipment to measure that. I did duplicate it on the ground, but it's more pronounced (meaning more events) in flight. There is a beacon as in ADS-B tailbeacon. There are strobes. I haven't tried checking for strobe/no strobe as a factor, thanks for pointing that one out.

 

[Bell206]

Okay. Lets back up. I know what random means... I wanted to know how you defined it in this context. Does it happen the entire flight? One time a flight? Once a minute? Etc. No need to get detailed like comparing to the engine firing. Beacon as in rotating beacon, but you said you have strobes. Duplicating on ground is a good thing as you can troubleshoot in more depth. But when did you 1st notice it, after some maintenance? However, check to see if the strobes causing it first and we'll take from there.

 

[JMichael]

Yes during entire flight and while the engine is running. Popping is several times per minute in flight, say every half second to two seconds. On the ground two or more seconds apart. The fact that it stops when transmissions are being received seems odd. No maintenance related event that I can recall. I don't have many accessories to turn off, mainly strobes, nav lights, and transponder.

 

[Bell206]

The fact that it stops when transmissions are being received seems odd.

Not really. It would depend how the interference is entering your radio system either radiating in or via the power wires. If radiated that could explain the silence. Given the noise rate is that fast (.5-2 sec intervals) may help isolate the source quicker. Start simple and see if you can isolate the noise further starting with the strobes, then move to the xspndr. And while at it see if the noise rate changes with engine RPM. But keep each test separate. But to confirm, no noise with power on but engine not running?

 

[JMichael]

Yes correct, I didn't hear it with the engine not running. And I didn't hear it on the handheld, which would seem to rule out radiated noise.

 

[Bell206]

And I didn't hear it on the handheld, which would seem to rule out radiated noise.

Not necessarily. Most radiated noise is not strong enough to "transmit" that far but it can radiate into unshielded wires in close proximity. Without the engine running and power on, turn on each power consumer and see if you can hear it, especially the strobes and transponder. And do you know if your ignition wires are shielded?