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RE: Question, FM on AO-40




Gary:

In order to have sufficient signal arrive at your receiver to make
FM usable, you would need to be louder than Leila would likely allow.
In addition to this,  FM is constant power.  For you to use your
fair share (say not more than you would if you were running SSB),
then your FM carrier power should equal the average power you
would transmit in an SSB conversation.  THis would lower the available
power to the FM to a point that it is almost surely completely
unusable.

Bob
N4HY

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Gary Gonnella
Sent: Thursday, October 23, 2003 8:32 PM
To: Amsat-Bb
Subject: [amsat-bb] Question, FM on AO-40


I don't want to start a argument or propose changing operating practices,
but why is FM forbidden on AO-40? This is a question that I have been
pondering for some time and would like other opinions.

With the passband limited to SSB or CW I understand that the average power
usage is considerable lower then a mode that has a carrier such as AM or FM.
I find it hard to believe that the average power level of FM would be any
higher than the digital modes being used presently. RTTY and PSK31 have a
constant carrier and SSTV has close to half of the bandwidth of FM.
I understand that the bandwidth consumed by FM is much larger then the other
modes but band congestion is not generally a problem with the satellite.

Given that the wider signal does not interfere with another QSO I see very
little difference in power between FM and SSTV, and there is a lot of SSTV
activity on AO-40. If I am putting 100 Watts ERP in SSTV or FM the satellite
should not be able to tell the difference. I understand that the Signal to
Noise will be higher at receive because of the wider bandwidth but that is
not the point.

Just some thoughts to ponder.

Gary Gonnella W6RYO
http://www.w6ryo.com


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