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Code to turn a RS41 into a Amateur Radio Foxhunting Beacon
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README.md

RS41-FOX - RS41 Amateur Radio Direction Finding (Foxhunting) Beacon

This codebase turns a Vaisala RS41 into a 70cm 'radio fox', suitable for use in amateur radio direction finding contests.

This is a fork of https://github.com/darksidelemm/RS41HUP, which is itself a fork of https://github.com/df8oe/RS41HUP.

Features:

  • Morse Ident containing callsign & current battery voltage.
  • Long CW beacon (user-defined length and number of repeats)
  • Low-Voltage Cutout, to avoid destroying rechargable batteries.
  • Beacon GPS position when battery is below a user-defined threshold.

Configuration

Configuration settings are located in config.h. Modify as appropriate before compiling/programming.

Compilation

(Currently only supporting compilation with GCC under Linux/OSX)

Programming

Either:

  • Use the ST Micro ST-LINK utility (Windows only), or
  • stlink under Linux/OSX (though I haven't had much success with this yet...), or
  • Use flash.sh with a Black Magic Probe. You will need to modify the path to the debugger's serial interface. I haven't been able to do the initial erase/program via this method.

Refer to this file for programming header pinouts. Note that you will need to power up the RS41 using the power button before you will be able to flash the chip.

Usage

  • Program as above.
  • Once batteries are inserted, press the power button to start transmissions.
  • Remove batteries to stop transmissions.

Power Consumption Notes

Power consumption of the various peripherals is approximately:

  • uC + other quiescent power usage: ~100 mW
  • Radio: ~170 mW (20mW TX Power)
  • GPS (Acquisition/Tracking Mode): ~210 mW

In the case of a stationary radio fox, there isn't much point enabling the GPS after the initial position fix, so we turn it off. This almost doubles our battery life...

Runtime Estimate

Achieved battery life will depend on your battery chemistry and transmit duty cycle. As a pessimistic estimate (assume 100% duty cycle, GPS disabled), we can state that the power consumption of the RS41 is 270mW.

Using 2x AA Lithium cells (~3Ah @ 3V = 9 Wh), we have a runtime of approximately 33 hours. Using 2x Alkaline AAs, (~2.5Ah @ 3V = 7.5 Wh), the expected runtime is 27 hours (if operating continuously), though note that the discharge curve of the batteries is quite different to the Lithiums, and the low-voltage thresholds will need to be adjusted appropriately.

Runtime Actuals

  • 2x Energizer Industrial Alkaline AA - 20mW TX, On = 10 seconds, Off = 10 seconds, Low Voltage Cutout = 0.5V - Runtime: 36 hours.
  • 2x Energizer Lithium AA - 20mW TX, On = 10 seconds, Off = 10 seconds, Low Voltage Cutout = 0.5V - Runtime: ??
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