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Re: PSK modems??



 
> Hi all:
> 
> I have a question about the Pacomm PSK-1 modem. I'm told that
> this modem is a decode only unit, and must be used in combination
> with a standard TNC.  I understand that LU-19, WO-18 and ao-16 all
> receive standard packet signals and transmit in BPSK.

What's a "standard packet signal"?  The 1200 baud Pacsats receive
Manchester encoded FSK signals from groundstations that are usually
generated with the aid of a Pacsat modem and a voice-grade FM
transmitter.  This is different from (and far superior than) the
AFSK-FM modulation used for terrestrial VHF-FM 1200 baud packet
communications and DOVE-OSCAR-17's downlink transmissions.

See my "Amateur Satellites" column in the Jan/Feb 1997 issue of
"Satellite Times" magazine for a description of the modulation
methods used in digital satellite communications.

> I was also wondering if one can receive messages and files
> from these birds with the PSK-1 without uplinking to the satellites??
> In other words, are the files "broadcasted" or does one need
> to send commands in order to receive the files??

You only need to transmit to request files or fill holes in files that
have been partially received.  Many times it is possible to receive
whole files and directory information with a receive-only setup.
 
> Since I cant afford the $500.00+ for a full blown sat modem, 
> I can at least find a used PSK-1 to receive image files from
> WO-18 and other data from the various pacsats. 

No one can afford $500.00+ for a full blown sat modem.

> Any suggestions??

Interface an inexpensive TNC to a homebuilt modem, and your total cost
for full-duplex communications will be reduced to something in the range
of $150.00.  If you already own a 1200 baud TNC, then your total cost is
reduced to probably less than $50.00 (ie: the cost of parts to build the
modem).

> Thanks , AB2CJ

No problem.  ;-)


73, de John, KD2BD

-- 
-=-=-=-=-=-=-=-=-=-=-=-=- John A. Magliacane, KD2BD -=-=-=-=-=-=-=-=-=-=-=-=-
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