Precidcting doppler shift on future passes?

I’m currently using a twin FT-817 setup for working satellites outdoors, and as I move to operating on the linear sats the hardest thing to determine is the doppler shift required on each radio to be able to find myself on the downlink.

I’ve not had any success in finding any Android apps that provide real time doppler adjusted freqs and so the next solution would be to use Gpredict before the pass to give me the offsets I need. Is there an easy way to do this using the radio control window? Or is there a different solution that I’ve not been able to find.

I guess that ultimately I could use a small computer to connect both radios to Gpredict in the field but I’d prefer to understand how this works, and actually work the satellites manually before automating it.

73 de Ciemon G0TRT

The radio control window can give you the Doppler corrected frequencies in real time and the pass prediction data can list the Doppler correction at 100 MHz during the pass. I think you will find it diifficult to work the linear sats manually.

+1 on not working linear transponders with manual doppler control. Please don’t be ‘that guy’ that users with doppler control have to continuously have to chase around the transponder passband.

Alex thank you, should the doppler corrected requencies window work continuously without radios connected? I only get one update per click of the engage button.

I know that working linear sats manually will be difficult but hard things are there to be learned about and practised until it’s not hard. Working FM satellites was hard until I understood my radios, my antenna, the satellites and the passes, and now they’re not hard to work.

Mark, if operators aren’t able or willing to chase a contact or work through their automated station then that’s fine by me. But this hobby is as much about learning as it is about operating. But so far no-one has been able to point me at a resource that can predict those AOS and LOS frequency shifts. Gpredict and other software can do it in real time, so they could be able to predict too, clearly that functionallity isn’t there. Maybe it’s a lost art.

No, it’s not difficult to do at all, but software designed to control rigs is really only interested in doing it in real-time.

As an example of how doppler can be programmatically calculated, here’s some code I use to generate a doppler profile simulating a transmission through a linear transponder satellite, using the pyephem library:

I didn’t quite remember tat but it looks like you are right.