Some rough and ready calculations *assuming a LEO* are that PSK needs the TX frequency adjusting every second or so, certainly over the duration of a short PSK transmission no Doppler correction on TX at 29MHz will result in no QSO.

But there's plenty of software which can adjust an HF transmitter so it'll just be a question of user education. Myself I would probably TX with my TS-480 and RX with a TS-2000.

PSK-125 may be a better option as it is on 6m when there's an opening (such as today).

Simon Brown, HB9DRV www.ham-radio-deluxe.com

----- Original Message ----- From: n3tl@bellsouth.net

I think it's a great idea. I suspect there will, indeed, be some Doppler challenges.

Although, I wonder.... How would Doppler's impact on PSK-31 be different from, say, SSTV? I ask because the SSTV schedules on AO-51 have been pleasantly surprising to me, in terms of the quality of image I was getting.

Some amplifying information on this HF transponder:

? long range = HEO / MEO or long range planning?

LEO

Some rough and ready calculations *assuming a LEO* are that PSK needs the TX frequency adjusting every second or so...

Yes, the good news is that Doppler on the 2m downlink does not impact the link, since it is FM. But still even at 29 MHz, 90% of the time the doppler rate is below 5 Hz/sec. See our original 2002 paper for PCSAT-2 and RAFT. http://aprs.org/psk31uplink.html

But this transponder has one big advantage, everyone's relative position in the passband is seen the same by everyone at the same time, and also, it is full duplex, so each stations uplink software can compensate his own uplink so that he remains exactly where he is.

10m/24m Transponder: Actually, I forgot that we had talked ourselves out of the HF/HF transponder since it would require TWO HF rigs to be able to operate full duplex. Instead we had changed it to 2m SSB uplink and 10m downlink. But then I guess it could be either. Come to think about it, so many rigs now have both VHF and HF, I guess it makes sense to go that way. But then the HF/HF inverting transponder would have only 3% of the Doppler and wouldn't that be a joy. As you can see, we have not made up our minds...

Let's go for it. I'm keen on using the unused "exclusive" HF satellite allocations. I hope many of us will be interested in supporting the concept. Bill - N6GHz

In order to get funding, we are proposing it as a "satcom" system for vehicles, boats and planes that only have old HF and UHF(AM) transceivers. Those low value platforms will never get satcom, but we can build a cubesat to provide it. Of course, it is just a demo with the UHF up and HF down, but all the rest of the time, we will have the links in the Amateur Satelltie Service bands for us. The UHF AM uplink would not be used for amateur radio, but the HF downlink would be available for the amateur transponders we mentioned above.

Bob, WB4APR

That was RS-12 Bob. I remember it well, trying the OTH contact's into the bird on the 15m u/l. I remember calling "CQ CQ RS12 LISTENING ON 10 METERS", and still having JA'S call me back direct, just to get the HF contact on 15m. Great fun. Radio Sport indeed....

73 Jeff fkb2m -----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of w7lrd@comcast.net Sent: Friday, June 05, 2009 2:46 PM To: bruninga@usna.edu Cc: amsat-bb@amsat.org Subject: [amsat-bb] Re: HF satellite?

For those who recall back in the day of RS-13 I think, was mode K. 15M up and 10M down. It provided some very interesting over the horizon contacts when we had good sun spots.

73 Bob W7LRD