up and down frequencies of VUSat, HAMSAT.
HAMSAT : downlink centrally : 145.90 MHz,
uplink centrally : 435.25 MHz. Bandwidth 0.060 MHz.
If the values
are correct, we find these two passbands :
435 MHz : 435.220.000
- 435.280.000 ( uplink
145 MHz : 145.870.000 - 145.930.000 ( downlink
and a mode B calc factor T ( f,T osc ) :
T (1) = 581.15
T (2) = 289.35 NON INV transponder
mathematical manipulations deliver the 'doppler shift compensated translation equations'
( INV transponder ) A1 and B1 .....
DS02 is 2m doppler
and DS70 70cm doppler value.
DS02=DS70/3 and DS70=DS023 .....
An example :
suppose there is a transmission to the satellite on 435.25 MHz (
centrally, the middle of the band ). The LEO doppler value ( on
70cm, DS70 ) for that moment is -8 kHz ( a LEO LOS situation ).
The coming back signal ( downlink ) on the ( ground station ) antenna
has now a frequency :
formula A1 RX=T-[TX+DS70]+DS02=581.15-[435.25+(-0.008)]+(-0.008/3)=145.90533etc.
concerning LEO satellites are changing less if AOS or LOS situations
exist ( concerning overhead passes,
also see http://www.qsl.net/vk3jed/doppler.html ). Therefore
it could be convenient to make such a calculation as above.
It is possible
to construct a SATELLITE MODE B
( included doppler shift compensation ) if you want. See the small
formulas I worked out. Some very good results ( examples ) : see
THE SATELLITE handbook ( ARRL edition ISBN 0-87259-658-3 4-3fig4.2
& 4-4fig4.3 ..... ).
Do not think
that an error in the result ( example above, the downlink frequency
) exists. Perhaps you expected a much lower value because the
satellite was moving away. Because of the combination concerning
this transponder type ( mode B INV ) and the doppler effects the
current result exists !
NON INV transponder, T ( f,T osc ) = 289.35 :
An example :
suppose someone transmits on 435.25 MHz ( centrally, the middle
of the band ) and the LEO doppler value ( on 70cm, DS70 ) for that
moment is -8 kHz ( a LEO LOS situation ). The coming back signal
( downlink ) on the ( ground station ) antenna has now a frequency
formula A2 RX=[TX+DS70]-T+DS02=[435.25+(-0.008)]-289.35+(-0.008/3)=145.88933etc.
Remark : both
uplink frequencies are the same ( in example 1 and 2 ), centrally,
in the middle of the band, but the downlink signals are different.
The signal, arriving at the transponder antenna, is not
centrally anymore ( because of the doppler influences ! ). The signal
is not anymore existing in the middle of the band. Both transponder
types give exclusively the same result if Fup=Fcenter.
If, after the
launch, now the frequencies are not quite correct ( because of 'drift'
of the oscillatorfrequency ), is it easy to find a new T-factor.
Perhaps you work with special equipments with very good tolerances.
After measuring and analysing you can find the new T-factor. Do
not forget the doppler values which act during the measurements