Friday, 16 November 2012

The mysteries of propagation

G4VXE and I had another little play on 2m JT65. Same QRG (144.165.000 if you're interested in joining us), same kit, same antenna, just 24 hours different.

Completely different ballgame. We had to go up to 20W, and only just completed.

It confirms what we all know, of course: that when bands are open, you need no power. When they're shut, you need lots of power and it's still difficult- these two occasions were more than 22dB different! You can't make that up with a linear. Even a linear AND a beam. The interesting thing is what's different about the two times. I don't think last night's "opening" was forecast by anyone or anything, and the band wasn't crowded with DX chasers.

We followed this up with a short burst of JT9-2. Clearly, JT9-2 wasn't designed for a closed VHF band, but there seemed little point in trying JT9-1, with essentially the same "floor" as JT65. Anyway, it was a spectacular failure, despite being able to see the other trace on screen and, in G4VXE's case, measure it as -22 - well useable.

We put the failure down to version incompatibility - I was on v0.3, he was on 0.2


  1. I've now grabbed the latest JT9 software. I see it's version 0.4!

    73, Tim

  2. Just grabbed it. Will be QRV with this tomorrow sometime...