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Re: mobile satellite operation...



On Wed, Jul 23, 2008 at 6:18 PM, Mark VandeWettering <kf6kyi@gmail.com> wrote:
>
> During one of the many recent discussions, somebody mentioned that
> Doppler tracking wasn't really that difficult, all one needed to do was
> download InstantTrack or whatever on some old, ancient PC, and that you
> would need to have a PC around to track the satellite anyway.
>
> But here's the thing: I _don't_ need a pc to track the sats. I operate
> handheld with my little TH-D7A in one hand, and my trusty Arrow in the
> other. Before each pass, I run a little Python satellite prediction
> program that I wrote to dump information about the pass, which looks like:
>
> AO-51 will be visible from grid CM87ux starting in 04:44:31 at 01:44:03
> 01:44:03 +0.0 132.0 K 18.8N 102.4W AOS
> 01:45:00 +3.3 127.9 K 22.3N 103.2W
> 01:46:00 +7.2 122.4 K 25.9N 104.0W
> 01:47:00 +11.4 114.8 K 29.5N 104.9W
> 01:48:00 +15.8 104.4  33.1N 105.9W
> 01:49:00 +19.8 90.3  36.7N 106.9W
> 01:50:00 +22.1 72.7  40.3N 108.0W
> 01:50:18 +22.3 67.1 J 41.4N 108.3W MAX
> 01:51:00 +21.5 54.1 J 43.9N 109.2W
> 01:52:00 +18.3 37.9 J 47.5N 110.5W
> 01:53:00 +14.1 25.5 J 51.1N 112.0W
> 01:54:00 +9.7 16.5  54.6N 113.6W
> 01:55:00 +5.7 10.0  58.2N 115.6W
> 01:56:00 +2.0 5.2  61.7N 117.9W
> 01:56:35 +0.1 2.9  63.7N 119.4W LOS
>
> At home, I know basically where the compass points line up, and for away
> from home contacts, I carry a little compass. With a tiny bit of
> practice and a reasonably accurate digital watch, you get pretty good at
> just tracking the antenna naturally over the course of a pass. With the
> FM birds, I just listen for the signal getting raspy, and tune down in
> frquency as needed.
>
> For me, I don't want to carry a PC. Or a laptop. I have my little FT-817
> that's actually pretty good to use on a strap around my neck, but if you
> have to sling a laptop and operate it all simultaneously, you're
> probably screwed.
>
> So, here's the idea: the Python library I wrote is actually pretty
> simple. It's a direct port of G3RUH's Plan 13 algorithm, and runs fast
> enough to be entirely useful. It also has the capability of doing
> Doppler translations at a reasonable rate, even on a fairly modest
> microcontroller. (In fact, the way I started on this project was noting
> that G6LVB's tracker implements the same algorithm to provide automatic
> antenna tracking). So, why not build a little battery powered
> microcontroller unit that provides Doppler tracking for the FT-817ND?
> You could load the orbital elements onto (say) and SD card on your PC in
> the house, and then jam the little thing into a smallish battery powered
> microcontroller, and it would provide automatic Doppler tuning. Then,
> truly mobile operation would be possible on the linear birds, without
> having to bring laptops or juggle with the reasonably fast Doppler of VO-52.
>
> Yes, the setup isn't quite ideal: you don't get full duplex, but in most
> other respects, it would be totally adequate.
>
> You could even use an off the shelf controller like:
>
> http://gumstix.com/store/catalog/product_info.php?cPath=26&products_id=79&osCsid=cb40b0a364041ad11ee9af494c9a518f
>
> which has a USB->host connection, two serial ports, and costs $129. This
> establishes a sort of greatest upper bound on how much such a project
> need to cost.
>
> What do people think? Will the lack of full duplex kill me in this
> endeavor? What am I overlooking?
>
> Mark "trying to turn ham radio into just button pushing" VandeWettering
> KF6KYI
>

Mark:

I've been thinking of something along these lines, too: a little pack
that plugs into the serial port of the FT-817, powers off its aux
power and does doppler correction using a PIC. The atmel ones have
floating point built in at a low cost, and I have one of these
breadboarded. Unfortunately, more pressing concerns have sidelined
this experiment.

My thinking is that the user interface would consist of a single
button and a speaker emitting CW so that one could select the proper
bird. It would have to have some way of connecting to a host computer
and get updated keps.

I suppose the smartest thing to do would be to build on G6LVB's code,
but I sorta' wanted to try out the atmel chips.

73, Bruce
VE9QRP

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