Quoting Stargate [email protected]:

Hi, Can someone point me to a website that explains the current digital modes and ways to use them? Also decoding telemetry from the birds, is there a "one size fits all" software or does each satellite have specialized software for doing this? Can you use Sound cards, TNC, specialized modems? I keep seeing references to 9K6, 38k6, and the like and have no idea what they are.

Also, are TNC's really necessary anymore? I've been away from amateur radio for over 10 years and things sure have changed.

I'm still putting my satellite station together and am down to picking antenna's and feed line. I am trying to build the station up for the future HEO birds as well, so what kind of overall db receiving level should I be shooting for?

Has anyone used "Gulf Alpha" antenna's? The cross polarized antenna's look very good to me. It wouldn't be circular polarization but I would be able to switch between vertical or horizontal with a flip of the switch.

All help appreciated, TNX 73's RoD KD0XX

Rod:

Your questions are numerous enough that I'm of the impression you would enjoy general introductions. I've found that the books offered by Amsat, as well as the ARRL's _Radio Amateur's Satellite Handbook_ are excellent starting points.

The AMSAT webstore has its publications at http://www.amsat-na.com/category.php?c=Publications I own _Getting Started_ (you'll want the 2006 edition), and I suspect you'll like the _Digital Satellite and Telemetry Guide_, too. Because AO-51 is a super test-bed for all this stuff, I'd recommend the book on it. If you want the latest on what's happening, get the Proceedings of the 2006 symposium. And if you haven't become a member yet, please do.

While there are other more expert than I on the subjects addressed above, I'll take a stab at answering them briefly. For digital modes, you can demodulate with a computer soundcard and appropriate software very easily at 1200 bps rate; the 9600 bps rate (short-form, 9k6) is more difficult to do in software, partly because your average soundcard link box for, say psk32, will likely use devices that limit the audio so that the signal cannot be demodulated. Apparently nobody has yet written software that can demodulate 38600 bps (or 38k6). If you're using a TS-2000 as your rig, there is more specific advice I'd be happy to give. So the need of a TNC is determined by what birds you aim to communicate with, and how.

Modulation schemes, alas, vary in satellite work, but you can do quite a bit with the FM modulation you might be familiar with from terrestrial packet, which I believe is designated AFSK.

If you're aiming for antennas that will work on future HEO's, such as P3E, I would look around the web for descriptions of systems that worked well on AO-13 and AO-10. My impression from such research is that you really will want fully circularly polarized antennas when that day comes, especially on mode B downlink: it's 3 dB that would take a lot of boom length to buy otherwise. Back in the day, it seems, people used 7 - 10 element circ. polarized antennas. Of course, it depends on how far the bird is: I just was playing around with the preliminary keps for P3E, and noticed that the distance can be as far as almost 50,000 km away, but much fun can be had at distances under 20,000 km. Plug that into the formulas in the books described above, and you have the makings of a wonderful night of system design!

You ask about a commercial antenna design. Might I recommend getting your feet wet in satellite work first with very cheap home-made antennas, say five elements on 145 MHz and eight on 435 MHz? I've had a blast with such units on the LEOs. They require far less precise aiming (you can do away with the elevation rotor), and are well-equipped for the job. They'll let you find the kinks in your system. You're also less likely to QRO the bird with such antennas. If you want to follow this way of thinking, there are many of us who can lead you to some dead-simple antenna designs that use Home Depot parts.

Either way you go, I note that you don't mention preamps. They are crucial. My strong recommendation is that you buy a mast-mounted SSBUSA or ARR brand preamp for each band that you plan to receive on. I think you'll have more fun with one of these hooked up to a vertical, than with a 20 element circ. polarized yagi that has no preamp.

Finally, if you're thinking ahead to the launch of P3E, don't forget S-band.

73, Bruce VE9QRP