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Date: Thu, 5 Oct 2000 12:23:26 +1000



The following is based on an email I sent to the Sunsat team after last
night's successful parrot pass over VK.  It contains a few of my
observations from the operation in this mode.  One warning I didn't add is
that parrot mode has proven to be very popular on its first day, so things
might get rather heavy in the Northern Hemisphere. :-)
 
For those who haven't worked parrot mode or heard SO-35's Mode B downlink,
the signals are huge, at least S9+20 and totally noise free on the downlink
with a small beam.
 
Anyway, here's the email...
 
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>The parrot repeater is working beautifully! :-) Signals were S9+ for the
>entire pass, comparable to local terrestrial repeaters for most of the pass
>(i.e. extremely strong, totally noise free needle bending signals). Audio
>quality was excellent as well, it's really working well! The mode was also
>very popular, with many stations taking part in the pass. Looking forward
to
>another session tonight. I'll do some recordings and put them up on the
web.
>:)
>
>Only hitch is the "blind" transmission into the bird, not being able to
hear
>other uplinks creates a little confusion, but I've worked out a couple of
>techniques that help. Might write the full thing up on my site, after the
>parrot passes have finished next week. :) But here's the basics:
>
>1. Don't put out a call on every 10 second cycle. Using alternate cycles
>gives other stations a chance to actually respond to your call, instead of
>you doubling with people you're trying to work!
>
>2. Respond to someone else's call, in preference to putting out a CQ
>yourself, this reduces the number of cycles required to get a coherent QSO.
>
>3. If there is a QSO in progress, wait till both parties have signed off
>before transmitting
>
>4. Keep it brief - parrot QSOs take longer to complete, due to the nature
of
>the medium. And don't Tx for longer than 10 seconds, or you'll discover the
>inherent "alligator!" :) ). Due to the limitations of simplex repeaters,
>each "over" takes over 20 seconds to complete (10 secs uplink, 10 secs
>downlink per over, plus courtesy tones), compared to a few seconds for a
>quick over in duplex mode.
>
>5. Under heavy conditions, putting out a call late in the 10 second uplink
>window may help avoid QRM as other stations cease transmitting, and get you
>a worthwhile contact.
>
>6. If standing by to give others a go, wait a minimum of 3 full cycles
>before transmitting again, more would be advised under heavy conditions, or
>take your one contact and log it as a success :)
>
>Anyway, catch you next time around. :-) This unique mode may not be the
most
>efficient way of working satellites, but it's interesting and is of benefit
>to stations not setup for multiple bands. Particularly well suited to
mobile
>and portable stations (though I do just as well on the more traditional
>modes portable :) ).
>
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Over the next week or so, I'll make more observations and refine the
guidelines for eventual web publishing, but hope these help.  And hope to
have audio from VK on the web within 24 hours.

Tony Langdon. 
Systems Development and Support. 
ATC Training Australasia.  Level 2 321 Exhibition St Melbourne  3000. 
Phone:  1300 13 1983     WWW:  http://www.atctraining.com.au
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