[amsat-bb] Re: mobile satellite operation...

Bruce Robertson ve9qrp at gmail.com
Thu Jul 24 16:46:57 PDT 2008

On Wed, Jul 23, 2008 at 6:18 PM, Mark VandeWettering <kf6kyi at 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¡ã 132.0¡ã ¨K 18.8¡ãN 102.4¡ãW AOS
> 01:45:00 +3.3¡ã 127.9¡ã ¨K 22.3¡ãN 103.2¡ãW
> 01:46:00 +7.2¡ã 122.4¡ã ¨K 25.9¡ãN 104.0¡ãW
> 01:47:00 +11.4¡ã 114.8¡ã ¨K 29.5¡ãN 104.9¡ãW
> 01:48:00 +15.8¡ã 104.4¡ã ¡ú 33.1¡ãN 105.9¡ãW
> 01:49:00 +19.8¡ã 90.3¡ã ¡ú 36.7¡ãN 106.9¡ãW
> 01:50:00 +22.1¡ã 72.7¡ã ¡ú 40.3¡ãN 108.0¡ãW
> 01:50:18 +22.3¡ã 67.1¡ã ¨J 41.4¡ãN 108.3¡ãW MAX
> 01:51:00 +21.5¡ã 54.1¡ã ¨J 43.9¡ãN 109.2¡ãW
> 01:52:00 +18.3¡ã 37.9¡ã ¨J 47.5¡ãN 110.5¡ãW
> 01:53:00 +14.1¡ã 25.5¡ã ¨J 51.1¡ãN 112.0¡ãW
> 01:54:00 +9.7¡ã 16.5¡ã ¡ü 54.6¡ãN 113.6¡ãW
> 01:55:00 +5.7¡ã 10.0¡ã ¡ü 58.2¡ãN 115.6¡ãW
> 01:56:00 +2.0¡ã 5.2¡ã ¡ü 61.7¡ãN 117.9¡ãW
> 01:56:35 +0.1¡ã 2.9¡ã ¡ü 63.7¡ãN 119.4¡ãW 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


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

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