Coming home one Sunday afternoon
I found a curious message on my answering machine. Kevin Dawson, VK2CKD had
left a cryptic message about the
Sydney
City to Surf fun run, mentioning
something about going in it. On returning the call I was told that we had
just got permission to use APRS in the race, placing a ‘tracker’ on the lead
vehicle. What I did not expect was being told that by that time next week
the race would be over.
With fear and
trepedation I told the WICEN team that I was prepared for the event.
After all I had presented talks on APRS to about 15 groups over the previous
6 months. How could I not be ready?
During the past few months I had
been preparing, hoping an event such as this would come up. I had been gradually
putting the equipment I would need together. I had enough equipment to be
able to track 2 vehicles, set up a repeater and be able to monitor the signal
on my laptop (The Equipment I used is listed in the text box).
Tracker in Start Vehicle
The tracker in the start vehicle consisted of 25 Watt
Yaesu FT-230R 2M Transmitter, Tiny-2
TNC updated eproms, a mag mount Garmin GPS-30PC
GPS, a mag mount 2m antenna and a 3 * 7AH gel-cell batteries. The transmitter,
TNC and one battery were in a laptop bag. The other two batteries were
in an old UPS case.
Digipeater
The digipeater consisted of an
old PK-88 with pre-APRS and
pre-GPS eproms
, a 2 channel Motorola 2m 25W radio and a car battery. The antenna was
a 1/4 wave verticle made from RG-213 co-
ax inside a 16mm conduit.
Reciever
The reciever consisted of a
kenwood TM-251 mobile, recieving
only, a PicoPacket
TNC, 25A power supply with 1.2AH of gell cells,
connected to a NEC Laptop (colour, 100MHz 586). The antenna was the same
design as the digipeater.
|
As in any events such of this type
there was no guarantee of any external power. That required me to be able
to run everything from battery power.
As well as getting all the equipment
set up I also needed to obtain maps for the area. This was both easier and
harder than it sounds. Maps are available from public domain sources, but
these needed to be digitised and calibrated for use. Luckily I had already
done some work with AutoCad Lite and Visual Basic
allowing me to simply get the maps out.
On the day of the race, I got up
nice and early for the drive into
Sydney. With some luck the
weather was much better that the previous few days - where
Sydney experienced a 1 in 100
year storm. Basically the weather was fine.
When people were assigned to stations,
APRS was left out. That required me to scrounge for
personel. With luck, Michael Roll, a newer unlicensed member of the
Waverly club was prepared to help me. It would aggreed
that he would travel with my mobile transmitter in the start vehicle to
turn it off if anything went wrong. Michael was given a UHF scanner and mobile
phone so that we could get him in that case.
Those wondering
if this is legal, the answer is yes. I set up the station with no
controls other than an external power switch. This clearly comes under the
definition of an unattended packet station, even if it is mobile!)
APRS in the 1996 Atlanta Olympics
APRS was used in the 1996 Atlanta Olypmics
during the marathon and cycling races to track the competitors - or the TV
cameras near the competitors. APRS
was never intended to be used on TV - It was just there to assist with
camera and helecopter positioning. However,
when the TV producers saw the results, they started using it rather than
attempting to read street signs from the video camera
foortage.
|
On the way to dropping him at the
start, we needed to drop the digi-
peater at the repeater site. This turned out to be a water tower in
Vaucluse. Not wanting to see how the people setting this equipment up were
going to lift the car battery for the repeater up the ladders I left them
to it.
Then Mike and I went to the Start
Line where the lead vehicle was stationed. Once we got there the driver had
no idea that they were going to have additional equipment and a passenger.
Some quick talking got the equipment loaded onto the 4-wheel drive. That
was after telling them all about how APRS got into the Atlanta Olympic Games.
After dropping off mike I then proceeded
to the finish line where I was to set up the reciever.
There were a few hassles here. The first was attempting to get the TNC
to receive any packets. This was solved by jugling
the modular connections on the radio and the TNC. The other problem was
a bit harder to fix - Attaching the antenna to the shed where the equipment
was located. The problem was somewhat solved by judicous
use of Duct tape.
What is APRS?
APRS is a technology for tracking objects such as cars and people using
1200 bps packet radio. APRS works by broadcasting information received
from Global Positioning System (GPS) receivers to stations nearby. Wide Area
Digipeaters are then able to broadcast
the information to an even larger area.
Stations receiving the information with the APRS software will have the
location of the object automatically appear on their screen. Digital maps
allow users to see what the area around the station is like.
The latest advance in APRS is the Mic-Encoder
or MIC_E. It compresses the APRS position report into
an packet that is only 200-300 mSec long, and broadcasts this at
the end of an over on voice repeaters.
For more information on APRS it is best to use the Internet. The following
sites contain information
| http://www.aprs.org
http://www.aprs.net
http://www.tapr.org
http://www.ozemail.com.au/~vk2tds |
The last site contains information on APRS in
Australia and
also details on the Australian APRS internet mailing list.
You may also get more information by contacting Darryl Smith, VK2TDS through
his email address - VK2TDS@ozemail.com.au
|
When I eventually got set up, the
race had just started - but I was not getting packets. I was hearing them
get through the repeater but I was not decoding them. Actually I was but
the packets were mainly the heading data rather than position data from the
GPS. This made all the transmissions for most of the first half of the race
useless.
Things improved once the packets
did not need to go through the digi-peater. At
the time I thoiught there was a problem but it
was actually working as designed. Basically I was not experienced enough
with the program nor with APRS.
I was only sending packets out every
1 minute. A more appropriate timing would have been every 10-20 seconds.
In the future this is what I will do.
Although there was little to show
because of the update times, the organisers were impressed with the concept.
The idea of being able to have an icon move accross
the screen automatically with the runnner is
is a great idea for this type of events.
Next year we might even have live coverage onto the Internet, and maybe even have the image brodcaset on TV.
|