A transponder does not translate by exactly the published difference —
the oscillator on board is decades old on some birds and a kilohertz or
two out. So an operator who sounds right to themselves comes back off
frequency, corrects it on the transmit VFO, and the tracker put it back
one second later, every second, for the rest of the pass. Reported on an
IC-9700 against HRD, which keeps the shift the operator sets.
The tracker already worked this way for the RECEIVER: it reads the dial
back and treats a move as the operator choosing a new station. The
transmitter had no equivalent — its comment even said so, "derived from
the nominal and never argued with". Now it is read back too, and the
difference becomes a standing trim on the nominal uplink.
Applied to the nominal rather than the corrected frequency, because a
translation error is a fixed offset in the uplink band and not something
that scales with the Doppler. Read only while not transmitting: mid-over
nobody is turning the knob, and on an Icom this read switches to the SUB
band and back, which is the same path TuneSatellite already uses to
write the uplink and not something to do under a carrier.
Kept per satellite AND per transponder, because that is what it belongs
to: the error is a property of the hardware in orbit, stable from one
pass to the next. Capped at 20 kHz so a bad stored value cannot put the
station outside the passband for ever, and shown in the tune panel with
a reset — an offset taken silently from the VFO has to be visible, and
the VFO alone cannot bring it back to zero once the operator has drifted
somewhere wrong.
SatTuner gains SatTransmitHz, implemented for the native Icom satellite
mode and for the Flex uplink slice; anything else reports nothing and
the uplink is left to the arithmetic, as before.
The hard part of satellite tuning is not the arithmetic, it is deciding
who owns the dial. A tracker that forces both frequencies fights the
operator every time they turn the knob to follow a station across a
linear transponder; one that never touches the receiver leaves them
chasing a signal that slides nine kilohertz across a 70 cm pass.
So the operator owns the receiver and the tracker follows them. Every
second it asks the radio where the receiver actually is. Where it put it,
nothing has changed. Further than a dial-turn's tolerance, and the
operator has chosen a station: what they landed on is converted back into
a nominal frequency, and the transmitter is derived from that. Which is
the division of labour on a linear bird — the operator listens, the radio
does the sums.
Three ways to reach the radio, because a satellite pair is a shape of
operating rather than a manufacturer's feature. An IC-9700 or IC-9100 is
asked for its OWN satellite mode: it pairs main and sub, gives full
duplex, and keeps the dials linked the way its designers meant, which is
always better than an imitation built out of split. A Flex gets two
slices, A the downlink and B the uplink, created when missing, because
"slice B does not exist" is not something to make an operator fix at the
start of a ten-minute pass. Everything else gets the downlink, and is
told so — half the job announced beats half the job hidden.
What goes in the log is the NOMINAL pair. Two stations working each other
through a transponder read different numbers off their dials at the same
instant; the only figure they can both agree on is the transponder's own.
FREQ is the uplink and FREQ_RX the downlink — the one place a satellite
QSO differs from every other kind, and the reason FREQ alone cannot
describe one.
rouggy