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I have a (actually two crisscrossed) 457kHz ferrite rod antenna from the internals of an avalanche beacon where 196uH <= L < 204uH and C = 560pF. I need to be able to evaluate the data from the receiving antenna's signal to determine the distance between the transmitter and receiver with a BeagleBone Black. Originally I thought I'd be able to wire the antenna up to the input of an ADC on the board, but after spending hours playing around with a beacon set to transmit and the receiving antennas wired up to an oscilloscope I realized that the voltage signal (mean, amplitude, and rms) coming from the antenna really doesn't fluctuate much until the transmitting beacon is within very close range. What parameters of the receiver's signal are used to evaluate distance? Is there any easy way to interface these two parts?

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  • \$\begingroup\$ Interfacing an antenna to an ADC falls under something called "software radio" and not just any old ADC can be used (though it being such a low frequenfy of 457kHz should make things a lot easier). \$\endgroup\$
    – DKNguyen
    Apr 30, 2020 at 3:54
  • \$\begingroup\$ I don't know anything about avalanche beacons, but I always thought those beacons only determined direction via an antenna and not distance? Like those animal trackers. \$\endgroup\$
    – DKNguyen
    Apr 30, 2020 at 4:00
  • \$\begingroup\$ @DKNguyen a lot of this RF stuff is really new to me. Modern avy beacons give you a distance reading in meters and they indicate the direction of the flux line they're picking up. They all have at least 2 antennas to prevent signal holes if the orientation of a buried victim doesn't line up with their buddy's transceiver. The old school analog beacons operated at 2.275kHz with 1 antenna and guided their users with audio tones. \$\endgroup\$
    – SCutler
    Apr 30, 2020 at 4:20
  • \$\begingroup\$ What parameters of the receiver's signal are used to evaluate distance? none realistically. You can DF the source by using antenna rotation but the amplitude of the signal received is a very poor marker for distance. \$\endgroup\$
    – Andy aka
    Apr 30, 2020 at 8:57

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Since you know the frequency, you might try either of these:

1) use an analog multipler such as MC1590

2) use a gated OTA such as CA3080 or (the triple) CA3060

3) build your own synchronous detector using analog multiplexors; remember to implement both Inphase and Quadrature channels.

4) use the NEE602 double-balanced mixer

ohhh you may want some narrowband upfront amplifiers. The standard IF transformers operating at 455+-5KHz should be fine.

In fact, just get an old AM radio, and attach your crossed ferrites to the output of the mixer.

You probably want to pose this as a new question.

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  • \$\begingroup\$ I'll look into those. Thank you! \$\endgroup\$
    – SCutler
    Apr 30, 2020 at 4:22

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