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I am an owner of a Yaesu VX-6R. This radio works great on amateur bands.

As a glider pilot I often need to hear the frequency of the local airport. I would like to find out whether this radio is suitable for listening on the airband.

Many times, especially when the antenna is not vertical to the ground, the frequency I am listening on is jammed (the squelch breaks — lasting for 1-2 seconds each time) and I hear something that sounds like humming from local FM radio stations.

I was wondering if the antenna (30 cm long rubber duck) has something to do with this. It is important to note that my other radio, a Yaesu VX-3, doesn't seem to have the same problem while listening on the same frequency.

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  • $\begingroup$ What modulation are the airport frequencies you are interested in? My understanding is that airband communications, regardless of frequency, are amplitude modulated (AM) for a bit more safety when communications overlap. Amateur handhelds for VHF/UHF would typically deal only with frequency modulated (FM) signals, though I suppose there could be exceptions. $\endgroup$ – natevw - AF7TB Mar 25 '16 at 20:12
  • $\begingroup$ Update: from a quick search, looks like the VX-3 supports at least AM broadcast bands on the MW frequencies, so I wouldn't be too surprised if it then also allows demodulating AM of airband as well. At this point I think I should reword this as an answer, assuming my suspicions about the airband communications are correct :-) $\endgroup$ – natevw - AF7TB Mar 25 '16 at 20:14
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The cheapest and surest way to test for this is to swap antennas, as both use an SMA connector for the stock rubber duck. Experience with a VX-5R found a similar problem with a cold solder joint on the jack, not the antenna, that was sensitive to orientation, but you can rule out the antenna by sw

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My experience, with a VX-5R, is that its AM receiver just isn't very good.

It will switch into AM mode when you tune into the air band, but because it's really an FM radio, there is no AGC on the AM. Distant aeroplanes sound much softer than near ones. Even if the voice is clear, it's soft.

So the squelch opening and faint hum that you hear might actually be a more distant aeroplane. Try turning up the volume and listening carefully for the voice.

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As explained in my comments above, I think your problem is this:

  • Airband communications are typically Amplitude Modulated, i.e. AM. (This has nothing to do with the frequency: just because they may be at VHF/UHF megahertz frequencies and close to FM broadcast frequencies, rather than MW kilohertz frequencies like broadcast AM in the United States, does not matter. Technically speaking, you can use any modulation at any frequency, albeit subject to legal/practical restrictions.) They use AM for safety reasons: amplitude modulated signals are able to combine over top of each other. They don't always combine perfectly, but hearing the mess of overlapping AM signals is better better than if using FM, where the strongest signal may simply win and you didn't realize someone else was talking. (See Tenerife airport disaster for an example where sadly it was still not enough to prevent an accident.)

  • Most amateur radio communications on VHF/UHF tend to be frequency modulated, i.e. FM. Other modulation is certainly allowed, and certainly used especially in specialized simplex communications, but far less common in typical use with repeaters and APRS gateways and whatnot.

All this to say: you need to verify that your receiver can demodulate signals of the type you wish to receive. It looks like the Yaesu VX-3 does support AM, and must be automatically selecting that mode for you. Apparently your VX-6R does not support AM demodulation, or at least it is not switching over from the usual FM mode, to the necessary AM mode, when you try to listen to the airband transmissions.

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