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I want to get a Garmin Astro 320 (or 430) which transmits GPS coordinates to a Garmin handheld unit on frequency 151.820-ish and 154.600-ish. But I would like to have the Garmin Astro GPS collar on my dog and receive the coordinates on a handheld APRS ham radio (thinking of getting the Kenwood D74A). Is this possible?

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    $\begingroup$ Hello Daniel, and welcome to ham.stackexchange.com! $\endgroup$ – rclocher3 Aug 25 '20 at 14:51
  • $\begingroup$ Apologies if I assumed wrong, but I added a "United States" tag since the frequencies (and possibly the protocols) vary in the models Garmin supply across the world: www8.garmin.com/astro-legal $\endgroup$ – natevw - AF7TB Aug 26 '20 at 20:50
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I don't know what protocol the Garmin 320 and 430 dog tracking collars use, but it is highly unlikely that they use AX.25 packet as their protocol, because that protocol is old and slow, and therefore harder on batteries. If they don't use AX.25-based APRS packets, then you wouldn't be able to receive the packets on a Kenwood TH-D74A.

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No. These collars do not transmit in the ham bands nor do they use APRS.

While many ham receivers can receive outside the ham bands, the protocol used by the Astro is proprietary, best I can tell. So to demodulate and decode it with anything except Garmin equipment will require some reverse engineering.

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  • $\begingroup$ Looks like the collars in question are MURS band, but it's possible the protocol is similar to that used by their RINO devices over FRS (for which they apparently got a waiver to send data — see e.g. this complaint). There are some preliminary notes and samples of that protocol on radio-active.net.au/web3/APRS/Resources/RINO and simply listening to the collars in comparison might provide a first pass guess as to whether they're similar. $\endgroup$ – natevw - AF7TB Aug 26 '20 at 20:38
  • $\begingroup$ There's also some potential hints at www8.garmin.com/astro-legal which reveal that at least several of the European variants of the Astro collar use GFSK. That doesn't seem in conflict with the RINO samples, but my armchair is a bit over my skis already :-P $\endgroup$ – natevw - AF7TB Aug 26 '20 at 20:46
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    $\begingroup$ The FCC certification info related to one of the collars itself (TT 15) that one would potentially be listening for can be found at fccid.io/IPH-0282320/Test-Report/Test-Report-2677489 and confirms GFSK for that US model as well. $\endgroup$ – natevw - AF7TB Aug 26 '20 at 21:23

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