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Re: RE: Eagle



On Wed, 18 Jun 2003, Greg D. wrote:

> the uplink doppler.  I found it was much more difficult to get into Mir's
> 70cm repeater, for example, because of the need to doppler-match the
> uplink for the station's receiver.

Very true. If a normal 70cm receiver is used with normal IF bandwidth, you
are absolutely correct.

But if the spacecraft designers simply used a 40 KHz wide IF instead of
the conventional 15 Khz (or even 12 KHz in Europe), then the uplink could
also be "no tune".  My guess is they didnt.

On PCsat we ordered special 40 KHz wide IF filters and for the majority
of the pass you could hit the UHF receiver just fine without tuning.

The tradeoff is losing around 5 dB in the link budget due to the wider
noise bandwidth.  But hey, everyone has 50W rigs for the UHF uplink which
more than made up for it.

So you are correct in principle, but proper design of the Mode-B (UHF up,
VHF down) transponder can mitigate that problem...

Bob


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