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

[pete <pho@crocker.com>]

Whats the baud rate of the downlink?
Pete N1AGV

Tim Cunningham wrote:

> 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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