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RE: Question, FM on AO-40

Bob Wrote:
> 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

Now we have a good discussion started.
I will confess, I have tested FM on AO-40 and found my signal readable when
it is 10db or lower below the beacon and well within the level allowed by
So as for the "fair share of power" I again can make the same statement for
SSTV. There is no question it is a very inefficient use but I maintain it is
possible without using anyone else's power.

Jim Wrote:
> Guess again.  SSTV has the same bandwidth of SSB at about 3 KHz (RTTY is
> narrower), whereas a narrow band FM signal (the commonly used FM in
> service) is 15 to 20 KHz wide.  Also, as a general rule of thumb, it takes
> a considerably stronger signal to hear a FM carrier than SSB.  PSK31 is
> designed as a very weak signal mode and both SSTV and RTTY work pretty
> with weak signals.

Jim I agree that the bandwidth makes receiving harder but if the power level
is kept within limits I don't see how the satellite would know the
difference. Also I find that SSTV is not great at weak signal level and I
maintain an FM signal at the level of a decent SSTV picture would be
copyable, although I would probably find it very tiring to listen to.

Gary Gonnella W6RYO

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