Sunday, March 20, 2016

Beginners - APRS

This morning I was asked if I knew of a website that had a good general over view of APRS. As much as I would have liked to provide and answer. I could not. So with a little help from an old owners manual I'm going to try and give an overview here..

With APRS you will need 4 items.

  1. Ham Radio Transceiver (Simplex 144.390 MHz)
  2. TNC
  3. GPS
  4. APRS Software
If you are not a Ham or Amateur Radio Operator. A transceiver would be a radio transmit and receiving unit used to communicate with radio waves through the used of specific radio frequencies. Much like your cell phone.

A TNC, is a Terminal Node Controller. It converts packets to audio tones and audio tones into packets. It does this by using the AX.25 Protocol at the Data Link Layer of the Network OSI Model. This allows for a computer or a TNC capable radio to communicate over the radio waves. Much like the internet of the old days with a modem. You would use a modem to modulate an audio signal over the phone line. Another example would be a fax machine.

A Global Positioning System, or GPS is recommended, but not a required item. You should be able to manually set your GPS coordinates. Though if you are mobile with a vehicle, its suggested that you have a GPS. Again not required but recommended. Some radio / TNC systems will just need a GPS antenna. While other systems might actually need a full GPS for you to connect to your TNC / Radio. Best to read your owners manual for a more proper answer to your gear. I've recently discovered a device called Mobilinkd, which uses your cell phone and a GPS.

Software is where all the magic happens. In more recent times newer radios have their own version of software. It actually firmware because it is inside the radio. Any software that is embedded in hardware is always known as firmware. Since the OSI networking model is being used and the AX.25 protocol in place of the Data Link Layer. Its just a matter of knowing a few commands / responses. You could actually run an older TNC in terminal mode and do everything manully by hand with a command line in a terminal window.

The APRS software program and registered trademark of Bob Bruninga, WB4APR. He has made packet communications much more exciting than before.This program allows you to track mobile stations on a map which you recall on a computer screen. Imagine seeing one mobile station moving on the map which can be scaled from .5 to 2000 miles. You also may be tracked on the computer screen of another station. For stations to be tracked must transmit beacons at certain intervals.


Now that you have an APRS setup. What can you do... ?

I'll tell you what I"ve done in the past.. you can go from there..

I've used it to allow up to a few minutes update as to where I am in my vehicle. Someone I know has a habit of calling my cell phone every 20 - 30 minutes asking where I'm at. Now I just provide a link in email and refer them to it..

other uses..

Tracking shuttles during large volunteer events.
Tracking people (portable APRS)
Weather Stations reports to local hams.
Relay short text messages from one radio station to another.

If you search around on the internet, you'll see there are many tracking purposes, and you might come up with some ideas of your own..

I hope that this provides you with enough information to get you started with APRS.


Tracy - KD6VZQ