From Dale N6JSX/8:
Local governments are getting up to speed to support the new LoJack SafetyNet system. I just attended an Indiana HAM/EMA meeting that this was the topic – asking HAMs to get up to RDF speed to support this system, that is already active in the area.
SafetyNet is a 215-217MHz tracking TX that is attached to an Alzheimer, autism, mentally challenged, or children ‘wrist/ankle’. It sends out a CW chirp TX signal every three seconds for RDF’ing.
I’m still working on getting more specifics on the TX but the whole TX/Ant/Bat is in a 1/2″ high half-dollar size container which means not much of an antenna and I suspect the TX is <30mW — so distance is not great. From what little I’ve seen the TX freq are down to the 1Khz, the one I saw was on 216.037 MHz.
My TH-F6A can RX 215-225MHz but the step is limited to 5KHz, however this signal is well within my usable passband. ComSpec sells a RDF RX for this effort ~$500, LoJack has RX units unknown sales info. I’m going to look at my AOR5000 can give me 1KHz resolution and SSB RX mode to increase detection sensitivity.
I’ll be soon posting in the FILES area ‘215-217 Tape-measure sniffer Yagi’ and a ‘215-217 Quad’ gain antenna designs.
As you can see this will require some good coordinated effort and mobile pattern movements to quickly obtain this QRP signal. So I see a mounted gain antenna on the mobile then switching to a sniffer when going to foot.
More info as I discover it. Check with your local EMA/Police if they are going to support this service – we may get some T Hunting action in remote no-where USA, yet.
This looks to be a wonderful opportunity to use some of the Radio Amateur’s Skills to help find “lost” people who’ve gone walkies.
Here is the URL for the basic tag: http://www.lojack.com/safetynet/Pages/index.aspx
More when Dale posts the antenna measurements and results of his follow-up research.