2m FM PSK Test

Last night I organised to have a play around on 2m FM with digital modes. I was curious to see two things:

a) Did it work; and
b) How well did it work.

I was pretty sure it would work – after all it’s just tones – but I wasn’t sure if there’d be any noticeable benefit. In the end I’d tee’d up a sked with Steve (VK2ZSZ) over in Queanbeyan at QF44op with me being at QF44mp. This was going to be an interesting path as it would require the signals to traverse at least one significant ridge line between us (probably an additional 200m ASL at it’s peak). Also, Peter (VK1NPW) had mentioned he’d attempt to join in but I was very dubious if that would work because I knew from experience that that path was a struggle (almost 100% unreadable) with voice – he being at QF44mo.

So in summary, we planned to try some PSK31 with the following stations all on basic vertically polarised antennas:
  • VK1HOW – QF44mp – 20W on a FT-7800 – 0km
  • VK2ZSZ – QF44op – 5W on a FT-817 – 15km
  • VK1NPW – QF44mo – 10W – 4km (that’s a surprise, I thought he was much further than VK2ZSZ)

What I found was that I was receiving VK2ZSZ at S4 with almost full quieting most of the time and 100% copy with close to 40dB S/N. VK1NPW was being received at S2 (about where the noise floor was – squelch was fully open as you’d expect) and I could copy him but had to keep manually adjusting the frequency in fldigi – and no S/N reading was offered by fldigi unfortunately. With VK1NPW’s signal I could also still see noise in the waterfall so definitely not full quieting.

As for signals between VK2ZSZ and VK1NPW, generally VK1NPW could not receive VK2ZSZ.

So what was seen was that we could get a very clear copy using PSK31 over 2M FM where otherwise voice would have been a real struggle (and at least with VK1NPW it would have not been possible at all). I would have also liked to switch over to simplex voice and try just for comparison, but we ran out of time – I might try and set this up soon just as a quick test with them both.

Therefore, the benefits (and enjoyment) of digital text based communication can even be realised on FM. Further, it was great to see the path over to VK2ZSZ as that was definitely a case of knife edge refraction and was a good enough path to even allow us to execute PSK-250 (unfortunately wider modes met a limit with computer processing power).

Thanks to both Steve and Peter for supporting me in this experiment. Hopefully there’ll be a few more in the future. 🙂
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