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Re: CQ PSK31 on Oscar 10



At 11:26 AM 4/23/1999 -0700, Clifford Buttschardt wrote:

>Very interesting questions regarding PSK 31 on AO-10.  I would be glad to
>join you in some experiments using that mode if it comes about.  Cliff
>K7RR/W6HDO   Morro Bay, Calif  CM95

The two real considerations for satellite transponder use are signal
bandwidth and transponder power/load.  PSK31 has an extremely narrow
bandwidth.  The carrier is not running at 100% as in FM/FSK and so it is
relatively transponder friendly.  I, for one, see no problems using/trying
this technique on AO-10 with regard to interference with other users or
overloading the transponder, provided one follows standard, prudent
operating procedures. PSK requires sharp tuning and the user will have to
compensate for doppler shift, but around apogee this is minimal, and can
even be controlled by a feedback loop to the mike click buttons.  Also,
when AO-10 is marginally illuminated the signal will show some mild FM'ing
which may make it harder to hold a "lock."   

Remember, both AO-10 and AO-13 had PSK beacons (at 400 baud).  If it's good
enough for the beacon, it's good enough for the passband :-).  We have
allowed and encouraged SSTV through the sats for years with similar
reasoning. The ranging measurements that the P3D group have been obtaining
on AO-10 are made through the transponder with 400 baud PSK signals without
difficulty.   

In my experience, the worst "transponder hammering" signals are the grossly
over-powered CW signals which can induce considerable distortion on the
transponder downlink in step with the keying.  This is a common experience
on the LEO's FO-20 and FO-29 where it's fairly easy to overload things.  It
was also a real problem on AO-13's S-band downlink which had a hard
limiting AGC.  I see PSK31 as having considerably less potential in this
regard than a CW "alligator."  After all, one of the advantages of this new
mode is that it does not NEED high power.   

Although I haven't tried PSK31 on satellite (or HF) yet, I've got the
hardware and hope to get to it shortly.  I think this is one of the
"neatest" modes to come along in quite a while. I say "go for it" and keep
us all posted on how well it works.  In fact, do it soon while conditions
are relatively good!  The weak signal aspects of PSK31 may allow for solid
contacts even through some of the QSB.  



-- 
____________________________________________________________________
Stacey E. Mills, M.D.  WEB:  http://www.people.virginia.edu/~sem2r/
Charlottesville, VA    E-Mail: sem2r@virginia.edu or w4sm@cstone.net  
			     Office Phone: 804-982-4406  Fax: 804-924-8767
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