[amsat-bb] Re: VO52
John P. Toscano
tosca005 at tc.umn.edu
Tue Jun 12 04:03:31 PDT 2007
> O.K. I have a Icom 820 and for field day I intend to try VO-52 with out computer controlled anything. I have Dos 6.22 , IT and a 386 notebook. Yagis for 2M and 70cm.
> Question should I adjust the transmit (70cm) or the receive (2 M ) for Doppler? I relize that either will work but this is a protocall question covering only the FD operation in June.
> Looking for some sound advise not lectures.
Without computer control, the conventional wisdom is leave the lower
frequency (2 meters) alone, and tune the higher frequency (70 cm). This
should apply on Field Day (lots of rookies) just as well as under normal
There may also be a preference depending on your specific radio. With
the Yaesu FT-847 satellite transceiver, the design of the radio is such
that in satellite mode with tracking turned on, the main dial controls
both uplink and downlink (that's what is "tracking"), and the sub dial
controls the uplink only, so you can correct for Doppler. In the case
of VO-52, the uplink is 70 cm so there is no conflict. But with Mode J
satellites (FO-20, R.I.P., and FO-29, hoping for resurrection) the
uplink is the lower frequency and so the design of the radio is contrary
to the "tune for Doppler with the high frequency". As it turns out, I
find the sub-tune knob on the FT-847 a real pain in the @$$ to use for
tuning Doppler, and impossible unless I put the radio into "Fast Tune"
mode. So I cheat. I turn on tracking, find a station by tuning the
main dial, TEMPORARILY disable VFO tracking, adjust the main dial until
I hear my downlink, then re-enable VFO tracking. At that point, I can
tune up and down the passband and the uplink/downlink frequencies stay
in sync for a short time. Obviously, as the pass progresses, the Doppler
shift changes, and about 3x as fast on the 70 cm band, so you need to
continue adjusting, but once you have your downlink and uplink
synchronized, if you REMEMBER to RE-ENABLE TRACKING, you can quickly
tune up or down the passband to another station and be at least close to
being tuned in on both.
YMMV with the Icom 820. It's been many years since I've seen or touched
one of them, although the first satellite contact I ever heard was made
on one during Field Day by an experienced satellite operator (N0BEL).
Field Day 2007 VHF/Satellite Station Manager, Twin Cities Repeater Club,
operating as W0BU from Minnesota. (We have been a 3A station as long as
I've been around, but this year may be a 2A station.)
More information about the AMSAT-BB