The story began with during a meeting between myself and Adrian 'Snow'
Dance, who has been working in Search and Rescue New Zealand for many
years, and who trained search dogs. His original website (but
now a bit out-of-date) can be found at http://www.k9nz.co.nz/ .
developed a system where the dog would carry a jacket, containing a GPS
and special electronics. The jacket had two 'tabs', who could be pulled
out, one by a person needing help, and the other by the dog itself. The
'tabs' had a small radio transmitter in them, which could be tracked
with radio finders. The track of the dogs, and special events like the
dog barking, and the tabs being pulled, would be stored in the GPS as
waypoints. The dog was trained to return to his handler who then could
download the GPS data to a computer, and trace the dog's track and all
events on the way.
my background as a HAM radio operator, I immediately asked, why don't
you fit the dog with a transmitter, so you have live data on his
was done, and ideas thrown around, options looked at and discarded.
Satellite tracking? Not an option with a dog tracking through steep
gullies and dense bush. Also the size and weight of the tracker was a
major issue. And how to get the data back to the dog handler, who
him/herself was out in the middle of nowhere, with no cellular
coverage, and who would need a satellite downlink to follow the dog?
No, the solution had to be using a direct telemetry radio link, with
the option of radio repeaters. But, it would have to be able to be used
by SAR New Zealand, without the need of a HAM radio operator to be
present. This meant that the radios had to be New Zealand Type
Approved, and that a suitable frequency had to be found and allocated.
this process it also became clear that this GPS radio tracking system
would be extremely useful for all SAR teams in the field. If they could
be live tracked, and shown on a topographical map at the forward field
base, this would make any search much more efficient, the controller
could see where his teams where with one look at the screen, send them
to any location, and be able to confirm that they indeed did search all
the required areas. There would also be a 'track record' for later use.
looked at the various options. We noted the ICOM system, but I did not
like the idea to have to rely on this one company for the whole system.
I would prefer a system that is fully 'open source' which would make it
customizable, and not reliant on a single company, who may change or
drop the system any time they liked.
obvious choice, for many reasons, was APRS, the Automatic Packet
Reporting System, designed by Bob
Bruninga in the 1980's .
The system itself is based on the AX25 packet protocol, which has been
in use for a very long time.
uses AX25 in the 'unproto' mode, which means it broadcasts a packet of
data without waiting for a reply or confirmation.
for APRS is readily available from various sources, and the firmware
which runs on this hardware is mostly 'open source', so if required it
would be possible to make changes in the way the system behaves. So far
this has not been necessary, and the existing 'trackers' are extremely
configurable. But APRS can do much more than just be used to transmit
GPS coordinates by search teams and search dogs. It is a full Radio
based messaging system in itself. In remote locations, just using
radio, and through Digital repeaters, it can send and receive messages
between laptops and even, if the Tracker has this capability, to the
Trackers themselves. For example, the forward controller can put an
'Object' icon on the topographical map, to indicate a special point,
and this will then automatically show up on the screens of all other
stations following, or participating, in the search. All without Local
Area Networks, satellites or cellular coverage. More on this
in the Software
For more information of the APRS system, check the new APRS website from
Bruninga at http://www.aprs.org/
we knew we where going to need a special frequency allocated, some
decisions had to be made regarding the type of modulation, and the
a full digital modulation system would be best (PSK, QPSK, etc.). This
means that the transmitters used would be of a special type, designed
especially for digital telemetry. The problem here was the cost of this
equipment. Unlike standard hand held radios, these units are very
expensive, and they had to be New Zealand Type Approved.
decided to stick to the standard system used by HAM radio operators
using APRS worldwide, which is a standard FM radio connected to the
Tracker by the microphone input and the speaker. This would
enable us to use of-the-shelf hand held type approved radios.
tests where done with APRS trackers in various situations, using the
HAM 2 meter and 70 cm bands. It became quickly clear that VHF had much
better penetration through dense forest than UHF. Also, signals
bouncing around hills came a long way further with VHF than with UHF.
it was going to be a VHF frequency. But, because our Digital Repeaters
would have to work very close to the VHF Voice repeaters used by SAR
and Police, we needed to be far enough away (in frequency) not to get
or give interference with these voice repeaters. In the end, we managed
to get allocated by RSM a nationwide channel in the EE band, which is
in the 170 MHz range, and several SAREX tests where our Digipeater was
installed next the portable Police voice repeater in the ESB band has
given no interference issues whatsoever.
development continued with the Trackers,
and the Software
program, which in the end we had to develop from scratch...
updated October 2009.