RF telemetry is producing a radio frequency pulse that your receiver is directly receiving.
GPS works one of two ways: 1. Transmits a signal on a regular time interval that a satellite system (e.g. Argos) receives and then that information is relayed through the satellite system and then through the internet to your computer.
2. The transmitter links to several satellites to get its own GPS coordinates and then transmits that directly to your hand held GPS receiver which then up links and finds its own satellite coordinates and then plots the two sets on its screen for the user to get a basic direction.
Drawbacks due to the first method is that you either have to have a computer, which even if you have a netbook to get on the internet in the field you still have to have cell service. Along with the fact that you will only get a location update maybe every 20 minutes, depending on the unit. And then the overwhelmingly high cost and the fact that most of these systems are for Biology and research only.
The second method is being used in dog collars now but people are having problems with this as well. The transmitter only last for 24 hours on a fresh battery and the amount of power and bandwidth required is going to limit range to about 5-7 miles.. easily 1/3 or much less range than that of traditional RF. And also a battery life comparison 24 hours for GPS Dog Collar vs. 16,000 hours for a similarly sized RF Dog Collar. All for about the same price..
The sheer power consumption of GPS is the main drawback, instead of a simple RF pulse you are looking at a complex modulated and encoded signal that has to be transmitted.. and this becomes very lossy over long distances.
Falconry transmitter have been made with one thing in mind, Helping you find your bird should it go missing, if there is no battery life or range then what good is it? It has to be small or the bird can't hunt. And you can have the most powerful transmitter int he world but if your receiver isn't sensitive enough to pick up the signal then its all for not.
These things aren't going to be dirt cheap as they are made in the USA and Europe, not China in bulk.
Hmm... I guess it doesn't work quite how I had thought. I had been thinking along the lines of your "option 2" that the GPS transmitters location was detected and triangulated by the satellites who then sent that location to the hand held receiver. In this case the range would be unlimited. Unlimited range and pinpointablility (I made that word up) were my main reasons for being so interested in this technology.
I've been looking into this a little bit more, First you need a receiver that can track 216mhz I found you can get a regular scanner from radio shack for $149-199 and then you need a Yagi antenna, $79 from mikes falconry. You do need to make sure its a continuous frequency scanner as some scanners leave out the 216mhz frequency.
I also found that 216mhz is used by not just the falconry fraternity but by the Hunting Dogs, Wild life tracking , maritime and a number of other interest groups. The argument that there was an economy of scale is therefore invalid as these manufactures are not making a few hundred of these units but thousand.
I did find that there is a section of enthusiasts in the ham radio market that radio track for fun and make there own receivers for around $200 . I asked a few questions and got told yeah you could modify there kit to work with the 216mhz. So if ham radio guys can make there own kits for around 200 and hand made. How is it a production line product costs twice to three times as much ?
so i would challenge companies to make a budget receiver in the $150 price point.