[ao16aprs] RE: [sarex] AO16/LU19/IO26 Renewed TRAKNET Interest

["Tim Cunningham" <tim_cunningham@mindspring.com>]

In order to serve as a gateway on AO-16 you will need a PSK modem.
The uplink requires Manchester FM which the PSK modem performs and
the downlink requires PSK.  Also, any TNC2 compatible can be modified
to transmit Manchester FM with a simple $3 modification.  The PSK
downlink is an entirely different story.

The downlink from AO-16 is PSK on 436.051 MHz which requires a radio
that has an LSB mode along with a PSK modem that can control the radio
to keep it on frequency as the Doppler shift walks the signal across the
band.  Ordinary programs that tune the radio frequency are not sufficient
to maintain a lock on the PSK downlink as the Doppler changes the
frequency.  The Doppler shift on the 70cm downlink is roughly 20 KHz,
meaning that the signal is about 10KHz higher in frequency as the bird
approaches and about 10KHz lower in frequency as the bird heads over the
horizon away from you. Tuning is very critical with the PSK downlink.  This
is
the tricky part of the process for automating it.

If we had a closed loop system that could detect a lock on the appropriate
frequency where the software could recognize this condition, then it may be
possible to feed that information back to the computer that a lock has
occurred and then let the tracking/ tuning program take over while still
maintaining a check on the lock, we might be able to automate the process.
This is an area that needs the most attention in order to make this a
successful automated process.  It is definitely possible.

If somebody wants to send a signal up to the bird I can turn my PSK
modem on and decode the downlink.  Everything here is automated
except switching the modem in and out with my other 1200/9600 modem
at the moment.


73's

Tim - N8DEU
Huntsville, Alabama


-----Original Message-----
From: Bob Bruninga <bruninga@nadn.navy.mil>
To: TAPR AO-16 APRS Special Interest Group <ao16aprs@lists.tapr.org>
Cc: TAPR AO-16 APRS Special Interest Group <ao16aprs@lists.tapr.org>
Date: Wednesday, August 25, 1999 11:58 AM
Subject: [ao16aprs] RE: [sarex] AO16/LU19/IO26 Renewed TRAKNET Interest


>On Wed, 25 Aug 1999, Schayk A.H. van wrote:
>
>> Oke i'm willing to give it a try.
>>
>> What do i need to get started, i've got a tnc2 (tf2.7b firmware), a g3ruh
>> modem with scc-card, a ts790e and duoband ant and a 70cm 10 element beam.
>>
>> will this be enough or do i need to invest in more stuf.
>>
>> 73 de Andre PE1RDW
>
>I am not familiar with all your equipment.  Any station that can receive
>the 1200 baud pacsats can do the Gateway function..  This then allows
>anyone with the modified TNC to transmit his position.status.
>
>This is a big experiment.  THere are no cook book solutions. We all need
>to flesh out our AO-16/LU-19/IO-26 capabilities and then see if we can
>make it collectively work for a common good...
>
>bob
>
>
>
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