Interference/Squelch Break on Radio

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avengineer

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avengineer
Hello. I'm an airport engineer that works with GA and commercial service airports. One of the GA airports I work at in Kentucky has had an issue with squelch break/intermittent interference across the UNICOM frequency for a few years. We've tried lots of mitigating efforts and have been able to make the issue go away for periods of time, but it always seems to come back. We know it's associated with the taxiway circuit.

Have any of you pilots experienced anything like this before? If so, do you remember when and at what airport?
 
Do you have access to a spectrum analyzer? That should be your first step in figuring out what kind of an RF environment you're dealing with.

Then make note of the aircraft/radio combinations that experience the issues.
Also see if it seems to happen when certain aircraft are in the area - a bad unit on one aircraft that radiates broadband RF will raise the noise floor and cause squelch breaks around it.
 
I've seen this twice. One was at KAWO Arlington before the Amazon fulfillment center and adjacent industrial park were built. I believe it was traced to a faulty base radio installation at a commercial poultry farm. The other is KRNT Renton. They have two huge radio towers near the field that (last I heard) still caused com radios on aircraft in the downwind to break squelch.

I have had individual pilots ask me about this problem in their aircraft that is not associated with a particular location. It usually turns out to be a cheap Chinese USB power bank or some other non-aviation RF noise emitter being carried in the cockpit.
 
wilkersk said:
I have had individual pilots ask me about this problem in their aircraft that is not associated with a particular location. It usually turns out to be a cheap Chinese USB power bank or some other non-aviation RF noise emitter being carried in the cockpit.
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^^^^ this .... I'll make a guess that there is something generating RF noise strong enough to blank the frequency. A spectrum analyzer with directional antenna (small yagi) would be perfect for finding the source. You might consider asking the local armature radio club for help too. These cheap chinese "wall worts" are notorious for causing this type of RF noise. The other is solar panels and the AC/DC converter.
 
I'll add, if you do suspect there is an errant RF noise emitter on or near the runway, the local amateur radio (HAM) club would likely love to help you track it down. See the ARRL article at the bottom of this page:

ARRL's Role in RFI Investigations​

 
Thank you all for your ideas--we've started chasing a few of these (and others we ruled out previously).
 
We had an issue years ago hearing a radio station occasionally cut in on UNICOM, never quite good enough or long enough to identify the station. The FAA and FCC brought in some equipment to better trace the source and found a nearby FM station had a "dirty transmitter" that was bleeding over other frequencies.
 
I had this issue last week at KTUS. I was doing my BFR and while we were taxing to the active, ground static just went off and wouldn't stop. Radio was showing 'Rx' in the window. The CFI thought it might have been us, so we swapped radios, still had the static. We called out to tower multiple times to check both, and they were reading us Lima Charlie with no issues. They couldn't hear any open static or anything. So we started to shut down lights, etc, thinking I might have a static bleed or something in the plane was causing the issue and the radio was picking it up as evident by the 'Rx' in both the radios. I'm all LED lights at this point, so I'm feeling pretty good its not that, but when we shut off beacon, the squelch cleared up. So we thought it was that, but then it immediately came back again regardless of my lights being on or off. After we did all that the CFI felt we ruled ourselves out of the equation and felt it was coming somewhere else. We requested to just go to tower at that point. We still had ground on the other just to see if anything changed. A few moments later, it just stopped on its own as we were holding short waiting. Just very odd. No issues at all when we returned.

I also occasionally get this squelch break static in an area east of the airport out past Benson when going East. And usually its when I am with ABQ Center on Flight Following. Again, I don't think it's me because it will just randomly clear itself up after a few minutes. I've heard other pilots share the same issue in this area. I don't understand what it means, or what I can even do, but it sure is annoying listening to it for a few minutes.

Is their an easy way to rule yourself out of the issue? Every time I hear squelch break and the static just drone on, I immediately think its something I'm doing, and my first inclination is to bump my PTT thinking something is stuck. But this is stupid because I'm always showing 'Rx' in the window when this happens, and never 'Tx'. So when I rationally think about this, I'm clearly not transmitting anything since there is no 'Tx', and clearly receiving since its always 'Rx.' This is one of those areas where I wish I had a better way to troubleshoot to at least determine if I'm receiving my own noise or if its something somewhere else, and I'm simply picking it up.

I have an IFD440 and a new PSEngineering audio panel. My secondary radio is a Narco MK-12E. Both seem to be in good shape, and in general seem to have clear coms normally.
 
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Squelch settings on radios are somewhat subjective - depending on the background noise and/or signals present at the time they were set. It is also possible for VHF (which includes aircraft comms) and UHF signals to 'skip' longer distances, depending primarily on atmospheric conditions at the time (known as 'tropospheric ducting'). We experience this at times in West Michigan, with signals crossing Lake Michigan.
 
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