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TinyTrak III Radio Systems
The Radio System used by the TinyTrak is by design very modular. The
TinyTrak III uses a wireless packet radio system called AX.25 which was
developed in the early 1980's as a specialised protocol for low bandwidth
wireless systems. The protocol was designed to be flexable, alowing tit to
stand the test of time.
AX.25
AX.25 is actually a version of the X.25 protocol modified for wireless
systems, with the addition of broadcasts and intermediate repeater stations.
These two features are the most important for the TinyTrak, and the APRS
system that it uses.
Being able to send broadcast data in a wireless system allows stations to
annunce their presence. It also allows these stations to transmit GPS and
similar data to the world without having to create a connection. In a
wireless system this is important, since creating and maintaining the
connection can actually cause a radio system to fail with the increased
traffic. APRS relies on the fact that broadcasts are most likly to work if
they can, and adding retries does not do anything but decrease the
reliability of the entire system.
Repeaters are also useful. AX.25 allows up to seven repeaters to be used -
source routing a packet. It also allows packets to be routed using internet
linked repeaters, and un-named repeaters to get the signal out. Since AX.25
generally runs half-duplex on a single radio frequency, the AX.25 repeaters
can be inexpensive since they exist of a radio modem that listens for a
packet and then re-transmits it on the same (or a different) frequency.
APRS
APRS is an OPEN SOURCE GPS/Weather/Short Message protocol that has beeb
developed for use on AX.25 networks. It is equally as applicable to almost
any other network imagineable. The APRS specifcation has been published by
the Radio R&D Organisation TAPR and is
available from the
TAPR www site
APRS is a highly scalable system, and is currently used by over 4000 people
in the USA today, all operating on the same frequency country wide. Thanks
to the internet this data is also available on Findu.com, and data from weather stations is
also sent to NOAA for integration into world wide weather reports.
Radios and Repeaters
As mentioned before, APRS and AX.25 can use almost any infrastructure - up
to and including satellites. The TinyTrak uses Bell MODEM tones in the voice
band of a radio to send the data. In general it takes about one second to
transmit one position report. It takes about one second for it to be
transmitted by every repeater.
No repeater is needed with the TinyTrak III, and any station that can hear a
TinyTrak transmission with a scanner can decode it. You can use the TinyTrak
through a voice repeater, or through a store and forward digital repeater.
We have successfully even placed a repeater onto a helecopter for one event.
They can also be used with CTCSS tones, allowing most stations to ignore the
data when shared with voice.
Conclusion
That is a simple overview of the technology of the TinyTrak, and the radio
systems it operates on. Radioactive Networks would be please to offer any
assistance we can with implementing an APRS system with the TinyTrak.
Who is Radioactive Networks?
Radioactive Networks is a consulting company with extensive
experience in mobile tracking technologies. We have used these technologies
successully in events as diverse as the Olympics, the IronMan
World Championships in Hawaii to a technology demonstration in Hollywood,
Ca. Our unique catalog of Hardware and Software allow us to provide an
economical solution to almost any business need.
Based in Sydney, Australia, Radioactive Networks have the experience
needed to complete even the most demanding mobile tracking projects.
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Welcome to our Techical Site. If you are interested in an overview, then visit our
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Copyright © 1994-2006
Radioactive Networks ,
darryl@radio-active.net.au
This page was last updated 2005-09-01 20:16:08
This page was last compiled 2006-02-21 14:50:14
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