following story is based on the fact that non Amateur Radio trackers
must use a "type approved" radio and be used on a frequency outside the
For Amateur Radio use, I now strongly recommend
the amazing Yaesu VX-8GR, which is a dual-band radio with build-in APRS
and a build-in GPS. This radio enables you do do Tracking and Voice
communication at the same time. And it is also capable of receiving and
transmitting Messages. More info on the Yaesu Website.
The original story of the development of a non-Amateur radio tracker
A lot of research has gone into the choice of
Tests where done to determine the range of VHF and UHF radio trackers,
especially in dense and forested terrain. This proved what we already
knew from our HAM background, that VHF signals travel much better
through forest than UHF.
The radio protocol we selected is APRS, which
Automatic Packet Reporting System. More information on this in the Technical Background.
has been in use for many years worldwide, and has a proven track record
:) And, it is fully open source, so there is a large source
hardware and firmware available, for very reasonable prices.
It is important that the transmitted packets are
short as possible. Reason is that the shorter the packet, the best
chance that they will be received without errors. And, more Trackers
can operate on the single frequency, including the Repeaters which also
need timeslots to re-transmit the packets. We use a highly compressed
format, which gives packets of a length less than half a
The drawback of this system is that we cannot use the full
resolution, we are limited to a resolution of 1/100 of a minute (as in:
169 Degrees 59.99 Minutes), and this translates to about 18
meters resolution on the ground.
We have not found this to be a problem
tests, as a higher resolution is not really required
the location of search teams in the field. Note that these teams
normally report their location in the New Zealand Map Grid, in a
resolution of 100 meters! However, the Trackers are field
programmable to use a different encoding scheme, which will add another
two digits, and which would (theoretically) give a
resolution of 18 centimeters. In reality normal GPS resolution is not
better than about 5 meters.
As for the hardware, we currently use a