Satgen344 Satellite Software Pt11    by GM4IHJ             28 Oct 95

Auto Track and Tune.  Anyone operating a modern Amsat has to be able to do
several things at the same time. In a typical Pacsat operation, the
operator must keep transmitter and receiver on tune, update the antenna
azimuth and elevation pointing regularly, operate the complex Pacsat up
and download protocols, and monitor flow up and down of the messages he or
she is interested in. This calls for computer assistance , and the
computer must be able to handle several software programs at once using
Multitasking and/or Terminate and stay resident, software. Several but not
all amateur radio tracking programs can be operated in this automatic
mode, provided that data from the tracking program can be coupled to
suitable antenna rotors , and, TX/Rx tuning systems. It is very necessary
therefore when contemplating a station operation of this complexity, to
ensure that any auto tune or tracking aid you acquire, is compatible with
your microcomputer, your antenna rotors, and your other software. Most of
the availble software and hardware is tailored for the IBM PC.

PLease remember , when using auto tracking, that it is only as good as the
relatively coarse antenna rotation systems used in amateur radio. Always
test system pointing accuracy by observing run ins from either direction
onto a fixed target such as the pole star. You may be surprised at how far
out the ordinary 1st order servo of a radio rotator , can leave you. 

In parallel with auto tracking , various forms of auto tuning are
available.  Some, such as that provided by G3RUH on his excellent PSK
demodulator , can work directly from the received signal operating through
your receiver up down frequency control circuits. This built in hardware
system is very accurate. Less accurate , because it depends on Keplerian
element predictions is auto tuning based on software operating through
your micro computer serial output , driving software controlling your
equipment tuning. Both these types of auto tuning are far superior to
manual tuning, which ceases to become a practical proposition at operating
frequencies of 430 MHz or higher, where doppler shift is fierce.

There are some exceptions to the above. At 435 Mhz a 9600 bps AFSK system
such as used by Uo22 or the Korean satellites is wide band and need only
be tuned three or four times even during a maximum doppler overhead pass.
By contrast smooth tracking of a 435 MHz PSK signal by manual means is
impossible. So if you are going to concentrate on 9600 AFSK only , you
should not need auto tuning , but you will find auto tracking is very
useful. Whereas a PSK satellite user definitely needs both auto track and
auto tune if he or she is to stay sane. Away from the Packet satellites ,
auto track and tune is useful for Oscar 20 Mode JA analog operation, and
will be needed next year for Oscar 22s successor JAS 2. However these auto
aids are not absolutely essential for Phase 3 type operation at Mode B or
mode J , because Ao10 and 13 move only slowly in bearing and elevation,
and doppler shift is minimal ,except at perigee, when omni directional
antennas are prefered.  The simpler Leo RS10, RS12 and RS15 satellites
should not require any of these automatic aids .