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Interference on 125.00 MHz (apparently an external ground issue)

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Feb 15, 2012
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At a local controlled airport, the tower freq is 125.0, so I have occasion to tune it, often fly simulated approaches there.

Five years ago, or perhaps more, I noticed a lot of background noise on that frequency, right in the area of that airport, sufficient that it would break squelch on my primary radio, an IFD540. The secondary radio, an SL-30, seems to handle the noise most of the time, and keeps it squelched. Normally I tune airport towers and "above" on COM1, but now at that airport use COM2 for its tower, so that largely side steps the issue. There is a customization for the squelch on the IFDs in the maintenance menu, but I haven't tried fiddling with that because this is the only issue I'm seeing, don't want a more aggressive squelch when it is not generally needed.

I spoke to the principal at the large avionics shop in town, and he confirmed the situation. He sees the same thing in many different aircraft and all kinds of equipment, because they do test flights after installs, and do fly to CYHM and tune the tower on 125.0. Initially (years ago) when he first encountered it, he thought it was install related, but after checking everything, and then seeing it in other planes assumed it was external. He also reports that this occurs not just in the area of CYHM, but only on 125.0 that he has noticed thus far.

I am wondering if it is some sort of interference from cellular stations with an intermodulation frequency clash, or some other newer ground communications network. Before five or so years ago, we did not see it.

I'm posting this to get a sense if others, in particular at areas distant from me, whether they are seeing this as well. I don't think I am going to "solve" the external issue, but more just academically curious.

* Orest
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