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1200 baud PACSAT Uplink



I was watching my manchester 1200 baud PACSAT modem on a scope and noticed
a skew in the data.  The high frequency components and low frequency
components were skewed by 6 dB.  THis is exactly what  you would expect
with pre-or-de-emphisis etc.. and its hard to tell if it is transmitted
that way, or is that the de-emphasis in my test receier?   But it raises
the question of WHAT DOES AO-16 want to see?  and how can I tell if I am
transmitting it right?

I have two PACSAT modems and the on-air signals appear quite different on
a scope,  even on the same packet.  How do I know which one is right?
Also we need a test procedure that does not require any special test
equipment.  So I am asking what the level of the two components should
look like on an OSCOPE connected to a typical 2m FM receiver.  This way,
we are all using the same eyeball.

   Since no one can visit AO-16 to see what the eye pattern looks like up
there, I am dependent on you successful uplinkers to tell me what a "good"
signal looks like by telling me what you see is the difference between the
two tones on your scope.  Just about anything in a full quieting signal
will work, but its the weak signal where a proper signal will gain many dB
over a poor one... right?

bob

P.S.  If I generate the manchester via an XOR and an R/C low pass filter,
then by definition, I am transmitting a skew of 6 dB between the high
frequency components and the low.  Seems like this is actually the
opposite of what is needed if a receiver with de-emphais is used on the
other end...  SO I am actually sufffering 12 dB of missmatch!  So you see,
knowing what AO-16 "likes" is very important...




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