Sunday, 26 January 2014

First delve into Digimodes

Oh, alright then, its not quite the first time! Yes, way back in the '90s I played 2m Packet for a bit, and more recently a bit of WSPR from the main station, and I am working on the WSPR 10m transceiver for demo purposes. And yes, I have spent a lot of time decoding utility transmissions in FAX, RTTY etc. But I refer here to my first attempts at live, 2-way QSOs in the interesting world of 31 baud Binary Phase Shift Keying.

BPSK-31, or simply PSK-31 as its usually known, is something ive recently begun playing with. I have FLDIGI software installed on my PC, and the necessary PTT and audio lines to the Alinco DX-70TH already in place. So, after monitoring received signals for a while, I tuned the rig up on 80m, set it to low power on USB, and into test load sent it a continuous alignment tone. My interface unit allows me to adjust the audio drive level, which I did to give me a 5w output signal, hopefully nice and splatter and IMD free. I then switched back to antenna, and started to climb the learning curve...

The biggest trouble with learning this mode, is learning the software! Yes, its a Keyboard to Keyboard mode, so in theory I just have to type the message, but that's remarkably tedious when you have to type callsigns etc. So I started to explore the software's Macro buttons, which do all that tedious stuff for you (in fact, it can do everything for you!) It seems the trick is to use the very clever logging features of the software. As a contact comes in, when the callsign is displayed, you click on it, and it goes into the logs 'callsign' box, all well and good. Do that for name and location also. And then, when the macro button is pressed, the software auto populates these details in your transmission! Clever stuff. The only bit I haven't worked out how to do is the signal report, I'm still doing that on the keyboard.

Another smashing feature I discovered of this program is its ability to simultaneously decode all transmissions within band in the selected mode, display them live, and search them for a key phrase, such as 'CQ', highlighting when it spots matching transmissions. All you do then is click it, and your tuned and decoding that transmission ready to reply!

First few goes with this then, once set up, I started to reply to CQs, and was very pleased to be answered and make the contact. Tally so far is just a few inter-European QSOs, France, Spain, Germany, Poland. But as a first trial at just 5w (the power of my cars brake light!) its very encouraging. I still haven't fully mastered the macros yet, so don't always get it exactly right, but I'm sure with time that will come.

I want now to get or build a low cost, QRP PSK transceiver, for demo use, to show just how accessible the hobby is. I'm looking for a 20m version of the Warbler-80, which is very simple, but does use specialist crystals. I'd very much like to build a PSK-20 from small wonder labs, but they are now closed as the proprietor has retired. However I have been offered one complete, if its a sensible price I may go for it.

PSK-31 seems to be ideal demo material. Simple kit, low cost, and can be run from laptops, tablets etc. It should appeal to prospective, tech savvy youngsters. It also has the advantage of low power operation, and for those who need to keep quiet, can be done with no sound at all! Ideal for late night operating.

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