Caledonia Amateur Vhf Enthusiasts

Automatic Packet Reporting System

APRS is a shareware program that takes advantage of the availibility of innexpensive GPS receivers to display the locations of moving stations on your PC. By connecting your PC computer to any radio network via an innexpensive ($130) radio data modem, then all stations can see the movements of all other stations. APRS permits any number of stations to exchange data just like voice users but without the complexity of maintaining separate point-to-point links. The primary APRS displayscreen is the MAP display. To help mobile units find each other, there are radio nets standardizing on several radio channels:

        144.39   MHz  FM  HAM radio VHF nets
         10.151  MHz  LSB Nationwide HAM tracking frequency
         27.295  MHz  CB  Channel 29 

APRS recognizes that one of the greatest real-time needs at any special event or emergency is the tracking of key assets. Where is the Event Leader? Where are the emergency vehicles? Whats the Weather at various points in the County? Where are the power lines down? Where is the head of the parade? Where are the VIP's? Where is the mobile TV camera? Where is the hurricane? WHERE IS THE FINISH LINE???

Included on the distribution disk are several README text files onapplications of APRS such as for weather nets, direction finding, plottingsatellite contacts, and tracking mobiles. In addition to the map display from any range from .5 to 4000 miles, there are several other data screens:

   LATEST LIST - A list of the latest STATUS beacon from each station
   POSITIONS   - A list of all station posits
   MESSAGES    - Operator-to-operator message to or from your station
   BULLETINS   - A page for BULLETIN ANNOUNCEMENTS to all stations
   TRAFFIC     - A list of the last 23 lines of messages from ALL stations
   ALL  LOG    - A time sequenced log of every new beacon or message sent
   HEARD LOG   - Shows a 24 hour history of who is on the air
   DIGIPEATERS - Displays routing information 


Although APRS automatically tracks mobile stations interfaced to GPS or LORAN navigation, it also easily tracks manual reports. Any station can place an object on his map including himself and within seconds that object appears on all other station di splays. In the example of a parade, as each checkpoint comes on line, its position is instantly displayed to all in the net. Whenever a station moves, he just updates his position on his map and that movement is transmitted to all other stations. To tra ck other event assets, any operator can simply maintain the positions and movements of all assets on his screen, all other displays running APRS software display the same displays. There is also a Tracking command on the P display that will cause APRS to keep the map display always centered on a selected object.


Some HAM radio satellites may not only transmit their current location, but can also be used for relaying station position reports between ground stations over large areas. The value of the map displays are in their ability to help students visualize the three dimensional geometry of an overhead pass.


APRS is an excellent tool for plotting the location of a hidden transmitter, balloon, or interfering signal. APRS will display the intersection of bearing lines from a number of reporting stations and also overlapping signal strength contours if only signal strengths are reported. Finally, APRS includes the Fade-Circle Search and Rescue technique which can be used by a mobile with only an OMNI antenna to locate a hidden transmitter.



APRS position reports can also include the wind speed and direction, as well as other important weather conditions. APRS supports a serial interface option to the ULTIMETER-II home weather station. With this interface, your station includes WX conditi ons in your position report for display at all other stations in the network and you appear as a bright blue circle, with a line indicating wind speed and direction.


As more and more digital devices on amateur radio include APRS position information in their routine BEACONS, APRS makes an excellent tool for displaying the topology of radio networks as an aid to frequency coordination.


In order to effeciently use the radio channel, APRS assumes that old information is less important than new information. Therefore, all packets are redundantly transmitted but at a longer and longer repition rate. Each new packet is transmitted immed iately, then 10 seconds later. After every transmission, the period is doubled. After ten minutes only six packets have been transmitted, and they stabalize to once every 10 minutes beyond that.


The keyboard is always active and responds to over a hundred different commands. Aside from selecting the major displays shown above,and manipulating the map display, there are several other sub-menu commands and the message commands:

  F1- Help            - Select from a MENU of HELP commands
  C - Controls        - Display a one line status of all control states
  F - FILES Menu      - For Loading/Saving files, or Replaying tracks
  I - Input commands  - Used to input posits, DF info or add OBJects to map
  O - OPERATIONS      - Several commands for normal operations
  M - MAP Functions   - Functions dealing with maps
  W - Weather Menu    - Displays the number of beacons per hour per station
  R - READ            - Displays your incomming and outgoing messages
  S - Send            - Sends traffic to a station
  E - Erase           - Erases outgoing traffic lines
  K - Kill            - Kills incomming traffic lines
  T - Traffic         - Displays message traffic between other stations


To see how the APRS system works on our frequency, use FILES-LOAD to load the file called FREQ579.BK. This file contains all the local stations on 145.79 MHz in our area. To see the tracking of the GPS equiped Army/Navy game football run, load the fi le named FBALL.BK and replay the file named FBALL.HST and select to see only FBALL, or CHASE1. To see the Marine Corps marathon event, load MARATHON.BK and replay the MARTHON.HST file. See Details in README.1st.


The positions of any moving station can be replayed either from memory or from a file. Tracks are kept in on-line memory until 150 have been saved, and then are saved to a HISTORY file. During REPLAY, use the Calls command to toggle on and off the di splay of callsigns, and use the HOME and page keys to center and zoom the map display if the mobile station moves off the screen. During replay, use these commands:


APRS can be found on this site or on most other Amateur radio bulletin board systems. All you need is the file and the regional map file for your area, either E, C, W, or may also find even more local maps for your specific state, such as CA, OH, TX, MI, IL, IA, and After creating an APRS directory, be sure to use PKUNZIP -d. The -d option assures that the complete APRS directory structure is re-constructed as you unzip the files.

cAVe Back to the cAVe APRS Page Updated September 23, 1998 archive n6fri