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Re: SSTV on the birds



On Tue, 29 Feb 2000, Joseph Trombino Jr wrote:

> I was ... surprised to hear SSTV .. in the upper end of the FO20 passband.
> ... I thought  heavy duty cycle ... formats such as RTTY, FM and SSTV
> were not to be used on linear transponders?

Maybe its time to consider being more flexible in our gentlements rules to
allow for variations in usage.  Maybe we should publish a table of the
agreed total transponder power AND the aggreed user UPLINK EIRP and the
MODE power effeciency.  Something like this (totally made up, fictitious
numbers):

     BAND    TOTAL PWR FULL RECOMMENDED MODE POWER POWER*BW
SAT  WIDTH   DOWNLINK  LOAD Uplink EIRP FACTOR     PRODUCT
---- ------- --------  ---- ----------- ---------- --------
FO20 100 KHz    1W      50   10W CW        .4          2
                        10   50W SSB       1         150
                         1   50W SSTV      8        1200
                         1   50W FM        8        7200
                         1   50W PACKET    8        7200

Then everyone could listen to the transponder and evaluate the current
pass loading.  If their chosen mode would not overload the bird, then it
should be permissible within the "gentlemens rules".  IE, one SSTV would
fit within the "rules" if there were only 2 other QSO's in progress...ETC.

Since some of the birds are so underutilized (some times in the middle of
the week, you can scan the band, and/or  call CQ until  you are  blue, but
there is no one on.  Then why be bound by rules meant to apply for the
worst case contest load?  Isn't this like the "dog in the manger"?

With over 20 operational satelliites in space with downlink power budgets 
ranging from .5 to 50 watts, It would seem to me to be in the best
interests of AMSAT(S) to clearly communicate to us users the technical
recommended operating modes and factors for each bird.  The gentlemens
rule of CW and SSB only seem a little outdated to me, when we have birds
flying overhead that NO ONE IS USING...

I think satellite operators would follow the "gentlemens agreements" if
they were clearly posted.

de WB4APR, Bob

I used the 8:1 SSB peak to average power considerations in the above
relationship between SSB and SSTV/PACKET/FM... I left bandwidth out, since
on most birds hardly any real bandwidth is being used.  If bandwidth were
also included, then its a real eye opener:

     MODE      PWR*BW
               PRODUCT
     --------- -------
     CW            2
     SSB         150
     SSTV       1200
     FM         7200
     FM PACKET  7200

THere is certainly room for some subjective modificaiton of the loading
factors or receommended max-loads to make this workable in practice...


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