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

Gould Smith gouldsmi at bellsouth.net
Thu Jul 24 18:53:20 PDT 2008

Hi Bruce ad Mark,

Howard's (G6LVB) Tracker 2 has the floating point code (using a PIC 18F620) 
and uses the Plan 13 and the Predict code to calculate the pass information. 
He has a stub for CW output.  The choice of the 4 MHz crystal obviously 
effects how valid the data is after a few days of service.

I have had a Tracker 2 running for months and been talking with Howard about 
some upgrades and combining features.  His code is open source and you can 
download it from his web site.
I understand that some of the code is a little compiler dependent on timing 

This new uC will fit in the same LVB Tracker board and can be programmed via 
a real serial port on the board. I recommend this as a good place to work 

It was designed to be run from a battery as a handheld unit.

Gould, WA4SXM

----- Original Message ----- 
From: "Bruce Robertson" <ve9qrp at gmail.com>
To: "Mark VandeWettering" <kf6kyi at gmail.com>
Cc: "Amsat-Bb" <amsat-bb at amsat.org>
Sent: Thursday, July 24, 2008 7:46 PM
Subject: [amsat-bb] Re: mobile satellite operation...

> 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
> 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


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