[amsat-bb] Re: Automatic doppler tracking of DSB

Jim Towler jtowler at xtra.co.nz
Tue Feb 5 23:35:30 PST 2008


Thanks for your email, which I have not included below, to save bandwidth.

You make a number of interesting points, and I might write more at a later

Regarding your point that there was little need to have good Doppler control
of the uplink, as its FM:

In general terms, this is largely true, and for a 2m uplink, little or no
tuning is required on AO-51/Echo etc. However, a number of earlier emails
spoke of the more critical need for AO-16 as it appears to have tight
filters compared to a typical FM uplink. Careful control of Doppler for the
uplink would allow a more full use of the entire filter bandwidth, rather
than using FM-Narrow, and having weak audio.

I still like the idea of attempting CTCSS, so may try this myself at some
point. I have the sometimes great advantage that sat passes here may have
only zero, one or two stations on, so it becomes possible to test or try
things that might be considered unacceptable usage or sharing of the
resource in many other locations around the world. If the sat makes a pass
to my East, I can be close to 100% sure I would be the only station, so
could test mostly anything I wanted that would not be harmful to the sat.
(The downside is that its also impossible to make a contact too.)

Not related to AO-16, but something I intended to test on FO-29 at some
point, was "two-station Doppler correction". Its not something I got around
to, but the plan was to get the exact locations of both myself and the other
station, and feed both sets of data into the Doppler corrections. The result
could be that the other station would use a FIXED uplink and FIXED downlink
for the entire pass, and the other station would do both. This would be
ideal for someone to have their "first go" at working a contact via an SSB
passband sat. HOWEVER, the signals would walk all over the passband on the
sat, so would be totally unacceptable except for short tests, and when very
few stations are in the footprint of the bird, as is mostly the case here in
New Zealand. Sadly, its too late for FO-29, but it is still an idea I'd like
to test. Again, I must repeat: This is NOT for use in busy parts of the
world, were many stations are in the footprint, as it creates a more extreme
use of the bandwidth.

New Zealand

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of James Whitfield
Sent: Wednesday, 6 February 2008 1:58 p.m.
To: amsat-bb at amsat.org
Subject: [amsat-bb] Re: Automatic doppler tracking of DSB

Many thanks to each of you who have replied to my inquiry.

 <<< Contents Removed >>>

More information about the AMSAT-BB mailing list