Re: [amsat-bb] ECHO Operations Planning

[Bob Bruninga <bruninga@xxxxxxxx>]

On Mon, 20 Oct 2003, Michael Kjorling wrote:

> wouldn't using wideband FM be a huge waste of spectrum?

Not at all.  We have 10's of MHz of bandwidth.  Not worth quibbling
over 0.2 MHz for the benefit of minimizing Doppler tuning.

> Yes, Doppler shift is a concern, but is it really *that* much of a problem?

Yes!  At 2.4 GHz, the Doppler on ECHO will be over 10 KHz per minute.
That means if we use normal 5 KHz FM, then you have to retune every 30
seconds...

> Also, how would this affect SSB signals

ECHO has no SSB downlinks.

> 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?

By using WFM downlink, then there is practially no downlink doppler and
everyone sees the SAME 3 KHz PSK/CW/SSTV bandwidth as the satellite sees.
Thus, each uplink station simply tunes his uplink to put himself where he
wants to be and everyone see's the same thing.

> 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.

The Doppler on AO-40 is +/- 60KHz over 12 hours.  On ECHO it will be over
10 minutes.

> 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?

Every Brodcast band FM radio is a WFM receiver.  You can buy an FM radio
for probably $5....

Bob

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