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Re: Re: [psk31] PSK-31 Satellite Donwlink Opportunity?



When using HF frequencies for satellite communications remember that the
very thing that makes these bands open for good terresterial DX is going to
make for limited access time to a satellite.  I recall that during the 2M
uplink and 10M downlink days of Oscar 6 the satellite had to be high in
elevation before the angle of incidence at 10M was sufficient for signals
to break through the ionosphere to reach ground stations.  This in effect
limited the downlink access time.  Additionally, since the 2M uplink didn't
suffer from this limitation it was possible for someone to QRM an existing
QSO because he couldn't hear his downlink on 10M as soon as the uplink
signal was heard by the satellite.  When the HF bands were dead, conditions
for satellite work improved considerably with respect to this limitation. 
When they were really open the satellite access was considerably poorer.

Bob Bruninga wrote:
> 
> On Mon, 26 Feb 2001, Jon Ogden wrote:
> 
> > > Ah, another very good point.  So if the INBAND is not such a great idea,
> > > then maybe 15 meters UP and 10 meters down. This solves many problems
> >
> > Why are we insistent on using HF for this satellite?
> >
> > If you are going to do this, why not use a simple 2m transceiver as the
> > uplink and 10m as the downlink.  Then it fits in the band plans and so
> > forth.  As for Doppler, well, heck, it can all be adjusted for in software
> 
> Good Question. The answer is Doppler, and also cheap $99 HF SSB XCVR kits.
> At 10m and below the DOppler is less than 600 Hz and so the Software can
> correct for it without having to have any radio control interface...  At
> 2m and above, the Doppler is 3 to 6 Khz and so there is no way to account
> for it in Software without having to re-tune the rig.  (or design a 6 Khz
> SSB xcvr)
> 
> There are many problems with trying to re-tune the rig under software
> control.
> 
> 1) It takes a hardware interface
> 2) It requires a computer controllable $700 to $2000 ALL mode Rig
> 3) Every radio is different, requiring multiple software modules
> 4) Most of the radios can not tune to 1 Hz precision
> 
> So it changes a simple concept (audio to a sound card) and maybe a $99
> xtal controlled SSB XCVR (see Warbler in this months QST) to the
> requirement for a $3000 Oscar class station...
> 
> My objective was to find a satellite design that would let many
> people use it easily per pass with simple equipment and such that the
> satellite can be built in a 4" cube and thus get an easy ride to space...
> 
> Also, by the time this gets to space, 10m and 15m will again be dead bands
> most of the time, hi hi.  By the way, I have not checked to see if
> satellite opertions is permitted in the new 12 m band under the ITU
> rules...
> 
> de WB4APR, Bob
> 
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-- 
73, Roy

Internet: w0sl@amsat.org
Home Page: http://home.swbell.net/rdwelch
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