One of the things that are key to having a pleasant experience working linear
transponders is software controlling your doppler shift. I’ve been a proponent
for manual tuning once when I was dismissing software control as something
for people who don’t know how. Well, let’s say I saw the light and leave it at that :).
Gpredict does a pretty good job but of course different than let’s say HRD which
I use when running Windows or MacDoppler on Mac OS.
In Gpredict you enable radio control by selecting the appropriate module in the drop
down menu on the right. Select your radio in the Settings portion of the window and
click on engage. On the left hand part of the window you can select your satellite and
the matching transponder (or beacon if you just want to track that) and click on Track.
Now when you click on the T button to tune the radio to the frequencies it never works
for me right out of the box to be spot on and I have to do some manual tuning.
While tuning manually, the Trace function on the radio needs to be off! Otherwise
you’ll be chasing your tail.
The way I do it is to leave the uplink signal where it is and then manually tune to find
my downling signal. Once that’s the case Gpredict keeps tracking both in sync and
you can work the satellite. So far so good one might think, but what if I want to change
frequencies? Clicking the L button links the two VFOs but unfortunately changes the
uplink frequency to what it thinks matches the downlink which is usually not correct.
The way I found a working solution for me was to first find my downlink, then turn on
the Trace function and on the linear satellites also the REV so that you track your
uplink frequency against (or in reverse) to your downlink frequency. Now I can tune
across the passband while keeping both frequencies close. It’s not a 100% match.
Once you’re at the desired frequency, you can then tweak the uplink to match the
downlink. Tuning the uplink VFO does not change the downlink, the other way around
both frequencies change.
While this sounds complicated at first, once you try it out it is pretty straight forward
and gives you the most control over where you want to be in the passband. After
tuning to the new frequency I turn the Trace function off in case I need to fine tune
the other station without changing my uplink.
This might work for other radios like FT-847 and IC-910H similar, I’m not familiar
with those so feedback is as always welcome.
73 Mike K5TRI