Re: [amsat-bb] Thoughts on future "FM birds" (was: proposal formaximizing fm le o contacts)

[Bob Bruninga <bruninga@xxxxxxxxxxxxx>]

> At 09:18 AM 8/17/00 -0400, Bob Bruninga wrote:
> >My design thoughts for a new analog SSB satellite for newcomers is:
> >   10 meters UP with users using 25 watt Radio Shack $139 10m rigs
> >    2 meters down for minimum doppler and greatest link budget

Mike Gilchrist responded:
> Many newcomers to the satellite ranks do not have 10 meter privileges.  The 
> RS birds use a 2 meter up/10 meter down transponder.  Most of your other 
> comments apply to this mode (A) also.

True, but there are some subtle but significant differences between
existing mode A and what I am proposing especially realtive to
satellite power and getting more people and newcomers involved in
satellites.

1) SSB uplink on 10m needs only a Radio Shack 10m transceiver ($139).
   Mode A needs an all mode 2m rig ($700?)

2) Using 2m as the SSB downlink requires only a 2m to 10m converter ($49)
   Mode A requires both the 2m SSB transmitter and 10m HF receiver ($139).

3) 2m down is quieter and requires less satellite power.  Mode A's weak
   downlink must compete with higher atmospheric and man made noise.

> Mode A (2 meter up/10 meter down) makes a very nice mode for newcomers and 
> others wishing to utilize existing equipment and antennas to work the 
> birds.  Doppler shift on either band is not severe.  Using standard 
> conventions, it is easy to tune the 2 meter uplink to keep your QSO in the 
> same relative portion of the transponder.

Yes, but still, the doppler tuning of mode A transmitter is 5 times
greater than doing the same on a 10m uplink.  Yes, the combined up/down
total is the same, but with 10m up, the smaller shift is on the uplink,
so everyone in the passband retains their relative position about 5 times
better and the whole group then moves greater relative to any particular
receiver.  Thus a 5 times reduction in the "sliding QSO" problem...

But you are right that it requires a proper license to transmit on
the 10m uplink.

de WB4APR, Bob


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