Finding the
two passbands of a linear mode B transponder. This is possible if
we know the downlink central frequency fc(dwn), the uplink central
frequency fc(up) and the bandwidth B :
upband:flowuhf=fc(up)-0.5B&fhighuhf=fc(up)+0.5B
dwnband:flowvhf=fc(dwn)-0.5B&fhighvhf=fc(dwn)+0.5B
Also we can find the mode B calc factor T ( f,T osc ) :
T (1) = fc(dwn)+fc(up)
( INV transponder )
T (2) = fc(up)-fc(dwn) ( NON INV transponder )
Some simple
mathematical manipulations deliver the 'doppler shift compensated translation equations'
( INV transponder ) A1 and B1 .....
A1 RX=T-[TX+DS70]+DS02
B1 TX=T-[RX-DS02]-DS70
DS02 is 2m doppler
and DS70 70cm doppler value. DS02=DS70/3 and DS70=DS023 .....
Concerning a
NON INV transponder :
A2 RX=[TX+DS70]-T+DS02
B2 TX=[RX-DS02]+T-DS70
Because of the
LIN MODE B NON INV function of this transponder we also can find
:
DS70=0.75[T-(TX-RX)].
If it concerns
mode J :
DS70=0.75[(TX-RX)-T].
If you want
2m doppler values ( DS02 ), replace 0.75 by 0.25 .....
And a LIN MODE
B INV function delivers :
DS70=1.5[T-(RX+TX)].
Perhaps you
are able now to construct the mode J formula if necessary. You have
to find :
DS70=1.5[(RX+TX)-T].
And if you want
2m doppler values ( DS02 ) again, replace 1.5 by 0.5 .....
You find some
calculations ( examples ) in : the VUSat transponder ( fourth submenu
button ).