Monday, January 12, 2009

Life in the Digital Age

When I was first licensed back in the 90's one of my first additions to the shack was a TNC. I spent many happy hours making contacts on RTTY, Pactor, and AMTOR with my MFJ-1278 multimode controller. I dabbled a bit with HF packet but only rarely managed a decent connection even with the "local" nodes in Alaska. With the addition of a 9600 baud modem board I was able to connect with orbiting packet radio satellites. I seem to recall that UO-22, KO-23 and KO-25 were the birds of choice back then. At the time it was all pretty cutting edge stuff. Nowadays everyone uses text messaging over the internet and cell phones but I like to remind people that hams have been communicating that way for over fifty years.

Right around the time I had to dismantle the shack in 2000 the first of the new "soundcard" modes were becoming available. Instead of an expensive box that used the computer only as a dumb terminal these new modes used the sound card and the computer to digitally process and generate signals. I remember experimenting briefly with the first generation of PSK31 software and the resurrection of the Hellschreiber mode. Ever since I got back on the air last year I've been intending to get back into the digital modes and see what has changed since the turn of the century. I'd been reading about the outstanding weak signal performance of some of them and thought that they might hold the key to communicating under the harsh HF conditions we experience in the far North. So, with that in mind, this past weekend I warmed up the shack and set out to get connected.

The first thing that had changed was the software. Instead of dedicated software for each mode now there are several "all-in-one" packages that do many different modes. I tried a few different ones but for the moment I've settled on MultiPSK by F6CTE. This versatile package includes all of the common modes (PSK31, RTTY, etc), all of the nifty new weak signal modes and some of the more esoteric stuff that I'm into like SSTV, HF FAX and HF SELCAL decoding. Thanks to a few sunspots I was able to make contacts in all the modes I wanted to try even with heavy QSB from the aurora.

First up was PSK31. Lots of activity on this mode but it suffers badly from the phase distortion of the aurora. Strong signals (S2 or better) were solid copy but weaker signals frequently produced gibberish. Still, I had no trouble to complete a couple of contacts. I'm sure I'll be spending lots of time here once conditions pick up a bit more.

Next was good ol' RTTY. It also requires even stronger signals than PSK31 for good print. Furthermore, it is also very succeptable to QRM. My opinion is that RTTY has outlived its usefulness. I just can't see any advantage to using this mode any more. Outside of contests I haven't seen much RTTY activity and once the major contest sponsors start allowing PSK31 and other digital modes in "RTTY" contests I think it will seldom be seen on the bands.

One mode that I had experimented with before was Hellschreiber. Invented in 1929 by Rudolph Hell, this mode uses the human brain to perform the signal processing. Very similar to HF facsimile, Hellschreiber (the most popular variation on HF is called FeldHell) transmits and receives individual pixels of letters that appear on a scrolling strip on the screen (originally it printed on a paper tape). Even in the presence of noise it is easy for the brain to discern the exact text received. I found that I could copy signals that were up to 10 dB below the noise floor (according to the MultiPSK software). Even better than that is the fact that the transmitted signal is very low duty-cycle. This means you can run full QRO without hurting anything. All the other modes I tested are 100% duty cycle so even though my radio and amplifier are both rated for continuous duty I always back off 3dB (50%) in continuous transmit modes just to be on the safe side.

The most unusual mode I tried was JT65. Originally developed for weak signal VHF work it has also become popular on the HF bands. Using a very narrow bandwidth and some heavy-duty computer processing this mode can be used to exchange callsigns and short (very short) messages in a timed sequence. I was able to make contacts easily with stations that were 20dB below the noise (again, according to the MultiPSK software). On the downside, at a minimum 7 minutes to exchange only calls, grids, signal reports and a trivial message (like 73 NAME IS JOHN)... I just dunno. I'm undecided on this one. It'll certainly never catch on for contesting, hi hi. Of course using it for something like EME work is a whole different ballgame. Or is it? Like I said, I still can't quite wrap my head around this one but I just know I'm going to be making a bunch of JT65 contacts (mostly off the moon, I hope!).

I saved the best for last. Olivia. This is my new favorite digital mode. Olivia uses MFSK (Multiple Frequency Shift Keying) and two layers of Forward Error Correcting to enable error-free copy at up to 13dB below the noise. Of the several Olivia contacts I made, one was a 30 minute rag chew with VE2FSK (2500 mile path). His signals were -11dB S/N (not even moving the S-meter) the entire time but 100% copy in both directions. I also had a 10 minute QSO with LU6DLL (8000 mile path). Again, signals hovering around -13dB S/N, barely detectable on the speaker (never mind moving the S-meter!) and still perfect copy. If I hadn't overheard a stronger station signing SK with him I don't think I even would have noticed he was there. Wow! It is for this reason that Olivia (and JT65) by convention use dedicated 'channels' on the amateur HF bands. Info on Olivia, JT65 and the HF channel plans can be found at

So I guess my old MFJ-1278 is relegated to junk box now. My Kenwood TS-2000 even has a built-in TNC for 9600 baud packet so I don't even need the MFJ for satellites anymore. Ahh, progress!

1 comment:

Paul Gerhardt said...

Thanks for the QSO from NWT. I loved seeing the airport as I also enjoy flying...
K3PG Paul in MD