Rotten
Robbie's
Radio Trackers
This system is based on using either a cheap FM SCANNER or a HAM RADIO receiver.
There is a very good tracking system produced by Walston Retrieval in
Smyrna, GA. These tracking systems are relatively expensive.
When I was introduced to this problem about five years ago
I found the Ramsey "Rocket Finder" transmitter:
While Ramsey claims 1/4mi. for this transmitter it will
only do that with a HAM receiver and a Yagi antenna. With just a FM
scanner the range is closer to 300ft.
This is a FM transmitter. but it does not have either a tone generator or
a data generator. You have to provide one of those externally or just use
it as a CW transmitter. But with a straight CW transmitter it is hard to
use with either a FM scanner or a HAM band receiver.
THIS PRODUCT IS NO LONGER AVAIABLE!
This transmitter weighs just about 1oz. The power for this unit is 2 N-Cell Alkaline batteries available at your local grocery store or drug store. The cost about $3 for a package of 2.
This transmitter has a measured range of about 1/2 mile with a ham band receiver with a 19" whip antenna. That translate to well over a mile of range with a simple Yagi antenna. With a hand held VHF FM Scanner it will probably operate between 1/2 mile and 1 mile with a Yagi antenna.
We will be doing experimenting with receiving antennas this Spring (2008).
Most commercial tracking systems use purpose built receivers. These receivers are very expensive relative to VHF FM scanners and VHF Ham Handi-Talkies.
The cheapest solution is to use a common HANDHELD FM scanner. These can be bought on eBay for as little as $20. Handheld FM scanners come with a "RUBBER DUCKIE" antenna. These antennas are totally useless. A simple 1/4wave whip antenna will give twice the range of the "RUBBER DUCKIE". A 1/4wave whip antenna can be purchased from a HAM RADIO dealer. Or a useable one can be made from a replacement telescopic antenna. An alternate source is from an old set set of "RABBIT EARS" or the antenna from an old portable radio. An antenna up to 48 inches long is very useable. The longer it is the more range you will get. But to double the range from 40 inches you would have to go to 96 inches. That becomes difficult to walk with. The Handheld FM scanners have a sensitivity of .7uV.
The more expensive receiver is a 2M HAM BAND HANDI-TALKIE (HT). These units cost $100 or more on eBay. But they have 4 times the sensitivity (and range) of a FM scanner. These units have a FIELD STRENGTH METER. With the FIELD STRENGTH METER you can get a more accurate line on the transmitter. The 2M HTs are more complex to operate. And they also come with same stupid RUBBER DUCKIE antenna. The same kind of whip antenna can be used with the 2M HTs as I described above for the FM scanners.
The difference in range between a VHF FM scanner and a VHF FM Ham Handi-Talkie is about 2:1 in favor of the Ham receiver.
There are several possibilities for receiving antennas. This can be from a simple whip antenna, a small dipole antenna, a Yagi antenna, or even RDF antenna.
There is a tracking technique called "Shadow Tracking". This technique uses a simple whip antenna held in a position that your body provides a shield shadowing the receiving antenna from the transmitter. As you move around you can find the direction of the strongest signal.
TAPE MEASURE BEAM OPTIMIZED FOR RADIO DIRECTION FINDING