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I own a Tx/Rx Radio Direction-Finding (RDF) set for a sport called falconry, basically, locating & recovering a pet falcon after flight.

The Tx tag is at 218.025MHz from Marshall Radio Telemetry : Marshal Radio RDF Tag

The Rx is a 10-channel receiver, TRX-10S, from Wildlife Materials Inc. : TRX-10S

I believe all systems for wildlife tracking from different manufacturers are compatible and speak the same modulation language.

Now, I want to know the modulation technique used by the Tx tag, I have my beloved Rigol DSA815-TG spectrum analyzer, but the problem is that, as with all RDF beacons, the signals they transmit are intermittent. They have the famous "Tet...Tet...Tet..." beep fashion... so I can't see the spectral content for an adequate amount of time -- and that is only when I'm able to pick it up (some times the spectrum analyzer misses it...)

My -clear- questions are :

  1. What is the modulation technique used in those wildlife tracking beacons?
  2. Whether I knew a straight answer to (1.) or not, what is a reasonable setup with my Rigol to see the signal?

For reference:

Tx Link : Marshal Radio RT Standard

Rx Link : TRX-10S

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    \$\begingroup\$ Links to ALL devices would help the profoundly lazy and might in turn help you \$\endgroup\$ – Andy aka Mar 2 '14 at 17:06
  • \$\begingroup\$ I believe (without evidence) that pulsed DF beacons are generally CW. Refer wikipedia. \$\endgroup\$ – markt Mar 2 '14 at 20:07
  • \$\begingroup\$ @Andyaka : You have a great reputation buddy (I loved your digital filters PDF) I will add the links, but I assure you, there are no decent datasheets :D Tx Link : Marshal Radio RT Standard Rx Link : TRX-10S \$\endgroup\$ – ThunderStormer Mar 3 '14 at 7:12
  • \$\begingroup\$ @markt : I know, it feels that way :D but the question is CW FM or CW AM Or CW Narrow-Band FM \$\endgroup\$ – ThunderStormer Mar 3 '14 at 7:12
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Rather than use a spectrum analyzer you might be best to use a receiver that can stay locked on the 218.025MHz carrier. One cheap option that works well at that frequency is a USB TV tuner capable of being used by SDR (software defined radio) software. For example see the RTL-SDR page.

There are quite a few software options listed at the bottom of the page but personally I've found the SDR# software to be good if you're running Windows. In the case of a periodic signal you'll also be able to capture it to a wave file for later analysis. Having said that I agree with the comment by markt that it’s likely to just be CW.

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  • \$\begingroup\$ Your answer is very helpful I'll try buying one.. (too bad I don't have sufficient reputation to vote your answer up) \$\endgroup\$ – ThunderStormer Mar 3 '14 at 7:20
  • \$\begingroup\$ That's OK, at some point you could accept the answer but I'd leave it a while yet - maybe someone is familiar with that particular product and knows exactly how it works. \$\endgroup\$ – PeterJ Mar 3 '14 at 7:24
  • \$\begingroup\$ No not yet, I don't accept it yet as a final answer. \$\endgroup\$ – ThunderStormer Mar 3 '14 at 12:10

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