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re: FM Sat Channel Spaceing 15 vrs 25k



>>> John Mock <kd6pag@qsl.net> 06/02/06 12:17 AM >>>
>I'm not at all sure about uplinks, and perhaps at 70 cm, 50 KHz 
>spacing  might make sense.... i'm not at all sure how this works 
>without computer control.  Perhaps it's not such a good idea 
>for birds intended  for use by folks just getting started.

But, no one that builds a 70CM uplink should ever use a standard
terresetrial radio with only a 12 KHz IF filter in it!  As you say, that
requires the sender on the ground to constantly tune in the blind
which is a big problem...

The correct way to build a 70CM uplink satellite receiver is with
a wideband (say 45 KHz wide bandwidth).  This is what we did 
on PCSAT-1 so that users on the 70 cm uplink also did not have
to tune for Doppler AND they could use their normal 70 cm radios.

The disadvantage of using a 45 KHz wide receiver to avoid any
doppler adjustments by users on the uplnks is that it ruins the 
uplink budget by 6 dB.  But this is not a problem at all, since
users on the ground have 50Watts, whereas the satellite
may only have 5W.  Again, this is why using all 2m downlinks
makes all downlinks not need any tuning, by the same token,
using a single 45 KHz wide uplink receiver on the satellites also
eliminates any doppler tuning on the uplink from a mobile
on 70 cm as well!

Again, ALL future satellites in my opinion,
1) Should be designed to be workable from a mobile rig and antenna
2) should have all downlinks on 2m where there is an 9 dB advantage
3) should have uplinks on 70cm where the worse link is made up
    for with more power from the mobile
4) Should have widerbandwidth uplink receivers on the satellite so
    the mobile does not have to tune
5) An alternate uplink or downlink could also be 10 meters...

Bob, WB4APR
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