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re: Full Duplex



On J-FM satellite with more than a few users on it, i think full-duplex is
essential.  Two reasons:  First, if you can't hear yourself, then it is 
difficult to tell if you are successfully being transponded.  Second, and
more importantly, if you can't hear yourself, you can't tell if you are
causing interference.  

More than half of the time i try to make a contact on AO-27, i stop half-
way through giving my callsign because i can hear that i'm not making the
bird.  On weekend transcontinental passes, this went up to 80%.  I hate
to think of how much QRM i'd be causing if i weren't running QRP and
stopping when i knew i couldn't hear myself!

Note that these remarks about full-duplex are in addition to transmitting
only when you can copy other stations' call signs.  Beginners who can't
hear the bird very well, and can't hear themselves, have completely
ruined many an AO-27 pass.

Furthermore, it's simply harder to do; i operated briefly in half-duplex
mode on a Hawaii trip and i found it challenging.  I found out the hard
way that not being able to hear myself was a SERIOUS handicap.  Maybe
it's OK on a lightly loaded bird.  I thought that there was so little
traffic on UO-14 over HI that i didn't need full-duplex but i found i
really needed it on a nearly vacant bird as well.

By the way, if you can't hear yourself on AO-27 (or equivalent) because
you're desensing your own receiver, then you're probably running too much
power (or your antenna needs tuning).  I routinely ran about 140mW on
AO-27 from California for passes west of the Great Plains and rarely more
than 1W when talking to the East Coast on a homebrew antenna comparable
to an Arrow.

My position is strong on this one.  If you are using Mode J-FM (or B-FM)
on more than a occasional basis, and/or especially if you are a beginner, 
you should NOT operate half-duplex!

		         -- KD6PAG  (Networking Old-Timer, Satellite QRPer)


[Note: I never send unsolicited binary attachments and if you receive anything
purportedly from <kd6pag@qsl.net> that isn't signed with my callsign, then it
probably isn't from me.]
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