Transponder Frequency Translation

 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=DS02•3 ..... 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 ).