[aprssig] CNSP-18 via ISS can work (FREQ MAP)

Thomas Krahn thomas at tkrahn.com
Tue Dec 4 20:19:59 EST 2012

A dedicated region for ARISS is actually not necessary.

You can simply use the Keppler coordinates to calculate the position of 
the ISS at any given time and then only transmit at 145.825 MHz when the 
ISS is close to the balloon's current GPS location. It doesn't matter if 
the balloon is over the sea or over a continent. The tracker could use 
every opportunity to reach the ISS. Listening stations on the ground can 
permanently listen on both QRGs or they could switch by a computer 
program that considers the ISS position and the last position reports of 
the balloon to predict at which frequency the balloon will transmit.

The tracker code is already implemented and opensourced to switch 
countries and the ISS. I pre-calculate the ISS positions to a table and 
store them in the PROGMEM of the microcontroller.
If you want details, email me directly.

Using the Kepler Elements directly would be more elegant but I'm not an 
experienced enough coder.

BTW some countries (like China and others) also use APRS on 70 cm. Is 
there any progress on getting a standardized 70cms frequency for APRS 


On 12/04/2012 06:54 PM, Robert Bruninga wrote:
> I overlayed a sketch of three 145.825 LAT/LONG boxes on G6UIM's APRS Freq
> Map that could shift FREQS over the Atlantic with 3 IF-THEN lines for the
> three freqs 144.39, 145.825, and then 144.800.
> See: http://aprs.org/transatlantic-freqs.GIF
> Bob, Wb4APR

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