Satgen343  Satellite Software Pt10   by GM4IHJ               21 Oct 95

HIDDEN EXTRAs -BLON, BLAT, FREQUENCY, MODE.  As discussed in satgen342 ,
Users must regularly update the Keplerian orbital elements of their
tracking software. This is a well established procedure with most software
providing automatic or semi automatic update procedures. But as software
is improved , each year sees more features added which themselves require
additional inputs of data by the user. Typical features of this sort are
Bahn Longitude (BLON) and Bahn Latitude (BLAT) which tell the software
where a spin stabilized satellite is pointing its antennas, so that SQUINT
angle , the offset between the line from the satellite to your station and
the antenna pointing line can be tabled, permitting assessment of
difficulty accessing the satellite. Other EXTRA features include the
accurate satellite transponder mixer frequency or beacon frequency to
allow exact doppler calculations , and , details of when and where the
satellite changes its operating modes as it goes around its orbit.

None of the above data features will be found incorporated in NASA or
AMSAT Keplerian element statements. Though some software writers locate
this kind of data in the same part of their programs as the Keplerian
elements.

BLON and BLAT data presently applies only to Oscar 13. It is published
regularly by Amsat . Oscar 10 no longer responds to stabilization commands
, and the simpler low earth orbit satellites are not stabilized to point
in a fixed direction throughout their orbit, so they are equiped with omni
directional antennas. Publication is made by Amsat at the same time as
satellite mode switching data is issued via packet radio bulletins or
Amsat publications. Dates are quoted when ever shifts in satellite
pointing are scheduled , so users of AO13 need to watch for these
bulletins and ( in almost all cases ) manually edit the appropriate
section of their tracking software data files

MODE SWITCHING data reports details of when during an orbit the transmit
and receive frequencies of the satellite will be changed. Because of the
need to use certain modes when the satellites antennas are pointing in a
certain direction, changes of mode switching times and Blon Blat changes
are usual synchronised , with a particular set of Blon Blat and mode
switching sequences lasting perhaps unchanged for one or two months . So
if your tracking software reports the mode in use at any particular part
of the orbit , you must check from time to time that your mode switching
data is up to date.

DOPPLER, some tracking software prints out doppler frequency data to help 
with up and downlink tuning. As explained in Satgen 336 , the actual
frequencies received and transmitted by the satellite are often slightly
different from those measured on the ground prior to launch. Individual
operators need to measure for themselves just exactly where their systems
tune by measuring signal frequencies when the satellite is exactly at
closest approach to their station ( ie zero doppler ). If you cannot do
this Amsat publish their versions of these frequencies from time to time ,
but be warned your individual station equipment ( particularly receiver
convertors ) is unlikely to be in exact agreement with anyone elses
figures. So if you can , measure your own figures and enter them in your
software.