Garmin Astro tinkering

[poolecw]

Hey guys, I stumbled upon your forum and hope you can help....

I have a Garmin astro dog tracking system. This gps tracking unit replaces the old radio telemetry systems used for dog or animal tracking. I use this GPS tracking system for hunting with hounds at night. The hound wears a collar with a transmitter. The collar transmitts gps coordinates back the my handheld gps unit. The gps unit then displays the hound's location on a map.

Eough back background info. I am trying to increase the range of this system. Garmin states that the unit has a range of 7 miles, which is highly overstated. In reality, I get about 1.25 miles of distance before I start loosiing signal with the hound. I bought a cheap aftermarket folding telescopic antenna off ebay and it improved range to 1.5 miles.

Is there an amplifier on the market that could work? I know of a guy that has tried this, but I don't know where he got the amp from. On a hunting forum, I found a picture of a modded gps system that had an amp in between the handheld and the antenna. (pic is below)

I would love to get some feedback and advice from you experts.

Oh yeah, the transmitter is on the MURS band.

Thanks,
Chris P

 

[Nursecosmo]

Your first, easiest and best option would be to use a gain antenna such as this one... http://www.arrowantennas.com/arrowii/arrowii.html
These guys can build a Yagi antenna to operate on any frequency you choose in the VHF band. You will need to specify which MURS channel you are operating on, as there will be a minor change in element length to get the best efficiency for the frequency. Use of one of these antennas should get you a range of at least 5-10 miles.

The MURS frequencies are as follows...
Ch 1 151.820 MHz
Ch 2 151.880 MHz
Ch 3 151.940 MHz
Ch 4 154.570 MHz
Ch 5 154.600 MHz

 

[dudmuck]

I was reading on qrz a thread about garmin astro.
One post seemed to say to be careful of RF front end overload of receiver with external antenna. It might suffer from intermod from other strong signals on vhf, or worst case be damaged by very strong signal. Or perhaps that was in reference to using an LNA with the receiver unit.

If you want to make it a hobby project, you could put some kind of bandpass filter or cavity on the receiver, with an LNA with overload protection that wont over-drive your receiver.

But if this is a real must-work application, there are all kinds of GPS to GPRS (cell phone) locator units that will work anywhere there is cell-tower service. These are made for pets, or children or whatever.

 

[coonhunter359]

a 3db rooftop

a 3db rooftop antenna works well out to 5 miles a bandpass filter will cutout off frequencies and even allow a VHF two way to be used on the same antenna