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RE: ECHO Operations Planning





> -----Original Message-----
> From: Michael Kjorling [mailto:michael@kjorling.com]
> Sent: Monday, 20 October 2003 10:37
> To: AMSAT-BB
> Subject: Re: [amsat-bb] ECHO Operations Planning
> 
> 
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On Oct 19 2003 19:32 -0400, Bob Bruninga wrote:
> 
> > MODE RX   DESCRIPTION               UPLINK      DOWNLINK
> > ---- --- -------------------------- ----------  -----------
> >  E   RX4 Experimental
> >  -       (HF) Multiuser             29.400      S-Band WFM
> >          (LV) Lband Voice           12xx.xxx    S-Band WFM
> >          (LB) Lband Bent Pipe       12xx.xxx    S-Band WFM
> >          (LD) Lband digital         12xx.xxx    S-Band Digital
> 
> Just thinking (and, as it looks, it's going to be a while 
> before I can become
> active on the amateur satellites), wouldn't using wideband FM 
> be a huge waste
> of spectrum? (There are wide S-band amateur allocations, but 
> not infinite.)
> Yes, Doppler shift is a concern, but is it really *that* much 
> of a problem?

Well, judge for yourself.  I have quantified the amount of Doppler for
various amateur bands for a LEO (based on an orbit the same as UO-14) on my
site at http://vkradio.com/doppler.html

> Also, how would this affect SSB signals (not just voice SSB), 
> and especially
> a situation where multiple SSB signals are present throughout 
> the transponder
> passband - say, a few CW users around 29.400 and a couple of PSK31
> transmitters at 29.402?

PSK-31 and SSB would shoot right by the passband!  I got the impression the
HF passband was going to be demodulated on the bird and then presented to
the WBFM modulator for the downlink.

> 
> I believe that today, computer control of radio equipment is 
> more of the norm
> than it has ever been. This makes automatic correction for 
> Doppler shift on
> both the up- and downlink quite feasible.

And locking the system up for only those who can afford the latest gear. :(
Computer control for me is not feasible, and won't be for a while as there's
many things higher up the priority list than a $2k-$3k rig (and that's the
cheaper end of computer controlled gear here).

> Some modes, especially high-speed packet, could probably 
> benefit a lot from a
> wide bandwidth link in terms of tuning ease. But voice and narrow-band
> digital modes (CW, PSK31)?
> 
> After all, what's the situation on AO-40? I don't hear people 
> complaining
> that finding and keeping your frequency relative to e.g. the 
> MB is hard, even
> when the satellite is moving very fast relative to the earth.

AO-40 moves much slower relative to the earth than a LEO.
> 
> If tuning is considered a problem for new satellite 
> operators, what about
> building your own WFM gear? Wouldn't that put off a lot more people?

Not as much as having to spend $3k on a new rig :)

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