A packet satellite can also be operated simplex (TX and RX on the same frequency). That means a single antenna and no diplexer for both the bird and ground station equipment. On Tue, Jun 7, 2011 at 10:16 AM, Trevor . <[email protected]> wrote:
> Hi Bob, > > I accept what you are saying about burst mode but it's possible to develop > a BPSK system that does burst mode too. > > A BPSK system with Forward Error Correction can offer a 16 dB advantage > over AX.25 1200 FM. > > As you say there's loads of FM rigs out there so receiving AX.25 is simple > and that's the reason everyone still uses it but for the future we should be > looking to more efficient means of communication. > > 73 Trevor M5AKA > > --- On Tue, 7/6/11, Bob Bruninga <[email protected]> wrote: > > > My pet hate is AX.25 1200bps FM > > [on] satellites... > > > ...But the reason AX.25 1200bps FM is still used > > > for new satellites is because there's so much > > > infrastructure, TNC's, PC software etc, already > > > inplace, it's the easy option. > > > > Actually, there is another very important reason. > > Link budget. > > > > With AX.25 one can have a 2W transmitter on a cubesat which > > has enough power > > to hit an HT on the ground with a whip antenna. The > > same cubesat running > > BPSK might be restricted to only 200mw. > > > > The difference is the Duty Cycle. The AX.25 packet > > only lasts 1 second say > > once every 10 seconds for an average power of 200mw. > > Which is the same > > power as the continuous power of the BPSK (200 mw) which is > > all there is > > available from the cubesat bus. > > > > But the advantage of the AX.25 BURST mode is 10 TIMEs the > > RF power to the > > user on the ground. > > > > For FM mobile-to-mobile satellite communications on OMNI > > antennas, that is > > why we use AX.25, to extend satellite links to mobiles. > > > > There are of course other issues and BPSK does have better > > performance for > > the SAME power, but as you say, there are not that many > > mobiles with SSB and > > all the hardware necessary to auto-tune the radio to track > > the Doppler. > > > > Bob, Wb4APR > > > _______________________________________________ > Sent via [email protected]. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb > _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
