FROSTBITE 96

Use of packet radio and APRS by Cheshire RAYNET.

Written by: Mike Tyrrell G6GAK Feb. 1996

Background

The use of packet radio on the Frostbite event has developed over several years. In 1994 a series of tests were carried out by a mobile packet station travelling to each checkpoint during the event and testing the quality of the radio path back to the control centre. These tests were carried out on a 70cms channel to avoid interference with the main 2m voice network.

It was quickly found that operating mobile packet is more difficult than voice. The mode requires essentially three pieces of equipment (radio, TNC and computer) vs. one (radio). As well as the challenge of engineering equipment and interconnecting leads to cope with the environment outside the shack it is difficult to operate over marginal paths. Whereas with voice communication it can be quickly established if the radio path is marginal this is not so easy to do with packet radio.

These tests highlighted the need to operate a packet station in a position which would have good coverage of the whole event, for example on top of a suitable hill. Mobile stations could then use this station (known as a NODE) to relay packets back to the main control.

For Frostbite 95 a packet network was set up with mobile stations at three checkpoints and fixed stations at the main control and the finish. RAYNET had been asked to assist in the production of the race results and the allocation of start times for both days. This was accomplished using the packet radio system while the conventional voice networks provided the primary function of safety communication.

In order to process the results a series of simple programs were written around a spreadsheet package. The checkpoints and finish stations filled in the times in the spreadsheet as competitors arrived and, on a periodic basis, sent this information back to control as plain text files. The files were sent using conventional packet programs (e.g. paKet 6.1) with stations connecting one at a time to the main packet control station. The use of the Node on a hilltop provided fair coverage of the course but there were still some problems with poor signal strength.

The use of spreadsheets was fairly successful (the results were produced in time for the prize giving!) but the method was found to be cumbersome and more information than was necessary was being sent from each checkpoint.

Developments for Frostbite 96

Analysis of the packet log files after the 1995 event highlighted three main types of information being sent between the packet stations :-

Competitor times.
How many people had passed through a checkpoint
The location of equipment or personnel (e.g. drinking water van, ambulance etc.)

Although the use of spreadsheets and conventional packet radio (i.e. where one station is connected to one other station at a time) was effective for the competitor times it was not efficient for 2 & 3. Often the information sent in by a checkpoint to control would then have to be sent out again to other stations.

A search for a more effective method to use packet radio to distribute this information found a suitable program known as APRS (Automatic Packet Reporting System). APRS was developed in the USA by Bob Bruninga (WB4APR). The software embodies Bob's experience over many years using packet radio for public service events.

APRS is widely used across America both for day-to-day amateur activity and during emergencies. The fundamental difference in its approach is that is uses unconnected packets to distribute information. This means that as soon as one station enters a piece of information it can be seen by all the other stations on the network.

As well as being able to distribute messages as text information APRS can also display the location of objects on a map. These objects may be either be placed manually on the map by the operator or, with the use of satellite tracking technology, they can be automatically displayed as they move about.

How APRS was used

The attached diagram shows the different types of stations used on the event.

At the event control centre two APRS systems were set up (these shared a single TNC and radio). One system was used to provide overall control of the network, the other was used as a "read only" system i.e. information could be read from the map and message lists but could not be modified. This provided an opportunity for people unfamiliar with APRS to see what it could do without the risk of interfering with the operation of the network.

Three mobile outstations were distributed around the course. These fed information into the APRS network on a regular basis. This was mostly done using the single line bulletin facility.

Some examples were :-

BLN2 :08:57 Control Main event 71 started. Fun event 80 started

G7LQD :13:50 CP4 71 started, 63 passed, 4 retired, 4 missed CP4 out

BLN8 :08:42 CP3 First runners through 111-2 and 303-2

At the finish hut a fixed station was set up using both APRS and a spreadsheet package. As the competitors arrived their race time could be calculated quickly at the finish using the spreadsheet. Provisional results lists were printed from time to time and posted on a notice board. Every hour or so the APRS program was shut down and a conventional packet terminal program was used to communicate all the latest finish times back to the event control centre. These were then used to printout results for people who had returned to the centre and to calculate the start times for the second day.

Two mobile stations were equipped with Global Positioning System (GPS) receivers, these stations were able to transmit their location automatically every few minutes.

The first of these tracking systems was used on the vehicle used to transport drinking water to the checkpoints around the course. Although this vehicle had an amateur on board it would have been impractical to inform control of their position by voice because they were always on the move. However, using the APRS map display the event controller could see their exact position, speed and direction of travel whenever required.

The second system was used as a "manpack mobile" with one of the RAYNET sweep teams. These teams carry out an important role to walk the course behind the last runners and locate any lost or injured teams before that section of the course is closed. Usually the control centre only know the exact position of the sweep team when they reach a manned checkpoint but with the use of the GPS they were able to continually monitor their progress as they walked along the course.

One of the most important things during the event is the location of the first and last teams. This is used when making decisions about moving people and vehicles around the course. In previous years control have keep track of this by recording the time at which checkpoint operators report the first and last team past their point.

A special feature in APRS enables the user to position a marker on the map and assign a speed to it. The software will then automatically move the marker along a predefined course at the given speed. This method was used with symbols representing the first and last teams, their estimated positions were transmitted every minute over packet and could be seen by any of the APRS equipped checkpoints. The estimated positions were manually updated by control when the teams actually passed a manned checkpoint. These estimates were found in practice to be very accurate and only minor corrections were needed over most of the course.

Day 1 of the event provided another good example of the use of the map display to communicate information. At around 8am, just after the event had started, an abnormal load broke down on the A41 close to the event centre. This was a route which would normally have been used extensively by support vehicles during the event. The load completely blocked the road for the duration of the event. By plotting it's position on the APRS map in control all the outstations could also see where the problem was and plan alternative routes.

Where to get more information

The Frostbite 96 event was the most effective use of packet radio to date by Cheshire RAYNET and the APRS software was shown to be more versatile for this type of activity than conventional packet programs. More information about the use of APRS on this event can be obtained from the author :-

Mike Tyrrell G6GAK 189 Runcorn Road, Barnton, Northwich, Cheshire CW8 4HR

Email 100321.1327@compuserve.com

Internet http://ourworld.compuserve.com/homepages/Mike_J_Tyrrell

There is a full description (written by WB4APR) of the capabilities of APRS in the book

PACKET: Speed, More Speed and Applications

Published by the ARRL

ISBN: 0-87259-495-5

The APRS program is distributed as Shareware, the latest version can be obtained from the TAPR Internet ftp site at

ftp://ftp.tapr.org/tapr/SIG/aprssig/upload/