Friday, August 13, 2010

Digital Mode Programs That Work #4: PC-ALE

It's not hyperbole to say that PC-ALE was the one program that totally revolutionized utility radio listening. It feels like forever since Charles Brain, G4GUO, suddenly appeared on the scene with a very functional Windows program for receiving AND transmitting in what was then the fairly new radio mode of Automatic Link Establishment.

A full description of PC-ALE would require a book. It's a big program, though it doesn't look it. It has a lot of parameters, and no one has ever fully explained some of them. There's no PC-ALE For Dummies. This makes it one of the more intimidating programs available to hobbyists free of charge.

Fortunately, the hams have taken it up in a big way, and they're driving most of the program's evolution. A few years back, it bifurcated into two major variants. These are a continuing refinement of PC-ALE, and a split-off called MARS-ALE.

As the names would suggest, this was due to the different needs of worldwide use in amateur bands (HFLINK) vs the more structured nature of the Military Auxiliary Radio System. Both of these programs are being actively supported by N2CKH.

Both of these have dedicated Yahoo groups. N2CKH maintains that MARS-ALE is actually the best of the two for receiving. I've experimented with it, and also with the newer PC-ALE versions, but the one I like best for completely personal reasons is still PC-ALE 1.071 Alpha.

MARS-ALE comes with transmitting blocked unless you have DoD authorization. Don't even try transmitting with PC-ALE until you've joined the HFLINK group, gone to its site, and read up on how to do this without destroying amateur-grade equipment.

PC-ALE comes fairly well configured for receiving right out of the box. I tweak a few things having to do with radio control, but these are different for every installation out there. Mostly, you want to make sure you've enabled the logging of soundings (propagation checks).

Frequencies are entered by a clunky interface and then you go to the "QRG files" menu and save them. QRG? means, "What's the frequency?" A QRG file is basically a freq list with associated parameters and network addresses to be used with that list.

You'd think that all the bugs in PC-ALE's basic engine would be out by now, but you would think wrong. As noted, the innovation has been driven by other needs, such as getting it scanning with all even semi-popular radios, or using IP networks with 3rd-party additions.

One nasty bug I've always had goes as follows. Stay with me, because this can really mess up your loggings. Let's look at an extract fresh from today's log:
[20:11:20][FRQ 23337000][SND][ ][TWS][ADW ][AL0] BER 0 SN 00
[20:11:20][FRQ 18003000][SND][ ][TWS][ADW ][AL0] BER 30 SN 08
[20:11:20][FRQ 17976000][SND][ ][TWS][ADWSPR ][AL0] BER 27 SN 07

What has happened here is that PC-ALE has created three different hits from what was one single long sounding on 17967. Most people will say wow, three freqs in one second. Well, no, because I've watched these appear on the screen and there have never, ever, been actual transmissions on these extra logged frequencies.

The dead giveaway is that the third of these shows a bit-error rate and SINAD of zero. Such a case wouldn't even decode. It's an obvious program malfunction caused by resuming scan while data from the sound is still being processed.

To be safe, I go through PC-ALE logs and eliminate doubles or triples with the same time and 00 measurements in the last one. Accurate frequency logging is worth it.

Just to confuse things more, the second two have truncated off the last part of ADWSPR due to technical reasons having to do with how all but the first three letters of ALE addresses are sent. Since ADW is also in use by Andrews AFB, it's easy to get confused here. These truncations can occur in any incomplete decode, not just mishandled sounds.

Another issue (not a bug) is the clattering of relays in many radios when they're being scanned. These peak the front-end circuit by switching filters as frequency is changed. If you're going to leave it scanning for hours or days at a stretch, this no doubt shortens their life.

Newer versions of PC-ALE have a "silent" mode which is said to stop this on some radios. I haven't tried this. On the NRD-545, I turn off the relays manually before starting PC-ALE.

Now that I've scared EVERYBODY off of PC-ALE or MARS-ALE, don't be deterred. The rewards are great if one gets the hang of either of these. Happy gurgling.