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Re: Satellite tracking programming ideas

At 02:26 AM 1/18/2008, Phil wrote:
>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?

Hi Phil,

If I understand your question correctly, there is yet another way to do this
which is seamlessly (i.e. it does not require any manual intervention at all
except for tuning the knob.)

Here is how it works in InstantTune:

1. Read RX VFO.frequency
2. Is the frequency different than the one you last wrote (within X hertz)?
         NO. User has not tuned, just go ahead and update TX and RX VFOs
         YES. User has tuned. Use the new frequency to set the new TX VFO
             and remember the new RX VFO frequency.
3. Repeat every 400 milliseconds.

The value of X, the frequency change minimum step size, depends on the mode
and the type of radio and sometimes the operating mode of the radio.

If you want to look at the code for how this is done, you can download it
from the AMSAT web site at:


Look at the source files named "control.hpp" and "control.cpp"

>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.

Again, in InstantTune, the frequencies are re-calculated every 400 
BUT the radio VFOs are only updated if they REALLY need to be. That 
depends on the
mode and the radio. Some radios are really annoying (beeping, blanking etc.)
so you only want to update them if you really have to  For the FT-100 
for example,
InstantTune only updates the TX VFO if it is off by more than 100 Hz. For the
TS-450, it is 10 Hz for SSB and 100 Hz for FM. The FT-847 is well 
behaved so it
is updated within 10 Hz all the time etc.

If you want any help, please email me. I also have a paper on radio tuning from
the 1997 AMSAT Space Symposium that I can send you if you would like 
an overview.

73 and best of luck with your projects.
Tony AA2TX

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