Hello Phil, you wrote:
This requires some manual intervention in that I have to stop the automatic tracking, turn the knob and then restart the tracking. This could take a few seconds which would mean that the tracking could be a few seconds behind. The alternative is to click on an up / down tuning arrow which will stop the tracking and adjust the received frequency. Clicking on a restart button would restart the tracking. I think that's the way satpc32 works.
SatPC32 works similar as Instant Tune (see Anthony Monteiro's detailed answer): With SSB sats the program polls the RX VFO once per second. If the result is equal with the previous one the user hasn't moved the VFO knob or tuned the frequencies via mouse or keyboard. Then the program can update the frequencies for Doppler correction if necessary.
If the values are different the user has moved the knob or tuned the radio via mouse or keyboard. The program then postpones a possible Doppler correction. It waits until it gets two equal values again (that means the user has stopped moving the knob). Then it calculates the frequency change the user made and recalculates and sets the new TX frequency like your program does and automatically continues with Doppler correction.
So, no manual intervention is necessary.
The program updates the radio frequencies for Doppler correction when the higher one of both frequencies has changed by a certain amount of Hertz. This "interval" can be selected separately for SSB and FM sats (typically 50 - 100 Hz with SSB and 300 - 500 Hz with FM sats).
Good luck with your project.
73s, Erich, DK1TB
----- Original Message ----- From: "Phil" phillor@telstra.com To: amsat-bb@amsat.org Sent: Friday, January 18, 2008 8:26 AM Subject: [amsat-bb] Satellite tracking programming ideas
Thank you for reading this.
I'm currently marooned because of flood water, and likely to be so for at least another week, so to pass some time I decided to upgrade my satellite tracking program. Disappointingly, playing with the current satellites in this country is pointless so the programming exercise is purely academic.
Originally, my tracking program displayed the link frequencies but I decided that was unnecessary since the radio has a perfectly good display itself. So to make frequency corrections, due to hardware errors, or to listen to another part of the downlink I simply used the radio's tuning knob. The program detected that the receiver's frequency had changed and calculated a new uplink frequency.
This requires some manual intervention in that I have to stop the automatic tracking, turn the knob and then restart the tracking. This could take a few seconds which would mean that the tracking could be a few seconds behind. The alternative is to click on an up / down tuning arrow which will stop the tracking and adjust the received frequency. Clicking on a restart button would restart the tracking. I think that's the way satpc32 works.
I've probably got too much time on my hands and both methods seem to work equally well. Does one method have an advantage over the other?
The update interval has to be fairly short so that a manual frequency change can be quickly detected. I'm currently updating the radio based on time. The alternative is to update based on frequency, say every time the higher frequency changes by 20Hz. This would lessen the number of radio updates during periods where the Doppler effect is at a minimum but does it matter if the radio is undated unnecessary? The rotator bearing is updated every ten degrees but that's to lessen mechanical fatigue.
Regards, Phil.
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