[amsat-bb] S band or any backup?
G0MRF at aol.com
Sun Sep 10 03:03:31 PDT 2006
On the subject of a parallel S band TX. That may or may not be simple
depending on what else is available inside Eagle. But in any event it should not
About two years ago when there was a similar period of outrage on the BB,
the hot topic was the wisdom of flying an untried or tested SDX transponder
without a switchable conventional 'linear' backup. I beleieve it was Bob who
announced "There will be no conventional linear transponder in Eagle" I was
very pleased to see Rick, W2GPS, leap quickly into the debate and reassure
everyone that the complicated DSP + logic in the SDX would be backed up by
conventional linear electronics. 'just in case'
In a recent mail the UV transponder has been referred to as having
unbelievably high audio quality. An apparent and very well justified comment on the
quality of the SDX.
What I can't recall seeing, is any reference to any fall back position of a
linear system as a back up.
It's worth remembering that 3 - 5 years time will be the peak of the sunspot
cycle. High solar activity, or an unfortunate error with the orbital change
burn as AO-10, could result in the satellite receiving a great deal of
It would be good to know that the linear backup plans have not been quietly
filed in the waste paper basket.
If it hasn't, then a parallel transmitter for S or any other band is very
simple to implement. Just split the IF, wire the other transmitter in parallel.
5W to an S band patch or whatever, and control it by turning the DC power
line on or off. S band amplifiers no longer need to run in class A with 30%
efficiencies, so an up to date class AB design would not be a large burden on
the power budget.
I suppose my quiet concern is not really the lack of S band, but; If the SDX
or 2m TX fails, what is left in the current design to provide a service to
the 90+% who will not have, or are not interested in C band?
Good engineering is important, but planing for the unexpected is vital.
Incidentally. It occurs to me that a disadvantage of having one major UV
transponder operating 24/7 is that while that concept removes the need for
complicated scheduling it will occupy 100kHz or so of the 2m band permanently
which may not be totally desirable in a limited 200kHz bandwidth. Presumably with
Eagle 2 and 3 under design / construction at the time of launch they will
have differnt bands. - Maybe 2390 - 2400 ish
Enjoying the debate
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