Something I don't understand about the D3 compensation: what is the purpose to send a pilot frequency from Italia or the Netherlands, so that the 3F1 satellite measures/observes the doppler shift versus a point in Europe
1) when a shift versus Perth has to be corrected ?
2) when the actual compensation seems to be implemented, not onboard the sat, but on the ground in Perth ? (why send a pilot freq. to the sat ?).
A communications engineer would be better placed to comment, but a couple of points:
a. it seems that the system design wanted the pilot frequency generators (for correction of the uplink and downlink Dopplers) on the ground rather than on the satellite. Perhaps this was to give flexibility in changing the frequency if needed, possibly due to interference, or to avoid having to provide on-board redundancy for that function.
b. the pilot frequency is received on-board at a shifted frequency, but this shift will be measured by the L-band receiver, so can be removed from the total Doppler on the pilot frequency when it is received at Perth.
This system concept seems to provide the required output parameter of the downlink Doppler.