Automatic Position Reporting System

Last updated April 3, 1999

Included in this file:

• What is APRS?
• Useful Applications for APRS
• Current Version Information
• APRS Maps
• Decoding GPS Sentences
• Mic-E (Microphone Encoder)
• How to Join the APRS SIG hosted by TAPR
• APRS Mobile/GPS Operations
• APRS Weather Station Operations
• APRS Direction Finding Operations
• SoCA APRS Digipeaters
• California APRS SIG Listserver
• SCDCC Listserver

 

• What is APRS? The Automatic Position Reporting System, APRS, is a system used for tracking objects, including people, vehicles, boats, aircraft, manned/unmanned balloons, even cows; weather systems, or just about anything using Amateur Radio.

  APRS was developed by Bob Bruninga/WB4APR, and was first introduced to the Amateur Radio Community at the ARRL Computer Networking Conference in New Jersey in 1992. Over the past five years APRS usage has grown and expanded across the globe. Many new features and capabilities have been added since its inception.

  In 1994, Keith Sproul/WU2Z, introduced the Macintosh OS version of APRS, appropriately called MacAPRS, at the 1994 Dayton Hamfest, and released it at the 1994 ARRL Digital Communications Conference in Minnesota. About a year later Keith, and twin brother Mark, released WinAPRS, taking full advantage of the windows interface. Both MacAPRS and WinAPRS are available via shareware fee off the TAPR FTP site.

  An APRS system consists of a computer (DOS 286 or better, or Macintosh color system), a TNC (take your pick), and a radio (HT, mobile, desktop) operating on VHF or HF, or both. A mobile APRS system is complemented with a GPS (one with data output), and a home-brew or store-bought port splitter for toggling location information to the computer. Routine updates in position are transmitted over the air, and show up as moving symbols on a map. This is similar to commercial systems found in rental or high priced cars, yet different because the information is transmitted over the air and displayed on computers running APRS.

• Useful Applications for APRS:
  • Disaster Response... Display APRS at your EOC. Emergency response teams equipped with APRS stand-alone trackers will indicate their location. Mobiles encountering blocked highways, fires, or other emergency, can plot the exact location. Voice reports from field units can be manually input and keep everyone online informed.
  • Race/Parade Support... APRS is an excellent resource for marathons and parades. Stand-alone trackers can be fixed to key vehicles tracking lead runners or groups, and report exact location back to the start/finish line staff. Emergency resources can be tracked and have their positions routine updated.
  • High Altitude Balloon Tracking... Here's an event that has drawn much interest. HAB events require alot of manpower to launch, track, and recover the balloon and its package that is released upon balloon burst at 90,000+ feet. A stand-alone package consisting of MIM, radio, and telemetry package (GPS, temperature, altimeter, etc) can downlink realtime data and allow tracking the balloon during its descent. Tracking crews manned with mobile APRS stations (computer, TNC, radio, GPS) can drive to the recovery area and quickly get the package back.
  • Manned Balloon Tracking... Much like HAB (above), ground crews can easily track the flight with APRS, even predicting potential landing areas downstream.
  • Routine Mobile Tracking... Probably the key to APRS "addiction". With a GPS providing automated location information, the TNC is routinely updated and keys the transmitter to send the current location to receiving stations. Mobile symbols can be modified to show car, truck, semi, RV, boat, bike, airplane, or any other common mode of transportation. For remote tracking applications no computer is required. If you want to track yourself and bring along a computer, a port splitter is required (build your own or buy one). Pictured here is the mobile setup in Dave Dobbins, WH6YC, vehicle. He can dismount the unit easily and store it in the trunk. From left to right: Agrelo DFjr, KPC-3, DFjr receiver, 2M/440 Voice, VHF/UHF Scanner, Packet 30W Amp, and Garmin GPS. Not seen, just below the DFjr, is an HTX-202 used for packet/APRS.

    

  • Weather Reporting... The "second best" feature of APRS, allows you to integrate inexpensive weather stations, like the Davis units, or those from Peet Brothers, and accurately record and report the wind speed and direction, rainfall, barometric pressure, and other criteria. Excellent for supporting weather nets and disaster response.
  • Boat Tracking... Similar to mobile tracking, a great way to track boats of any size. Trackers have been used for both VHF and HF operations, allowing those near and far to track the vessel as it cruises around the bay or ocean.
  • Manned Tracking.... Very similar to what's already been described, just the portable version. Running from internal battery power, a common system might include an HT, miniature TNC (like the Pico Packet or Handi Packet from PacComm), and a TripMate with batteries. The combo can be easily backpack mounted for a hiker or other person on routine trail tracking or hunting for lost persons in the wilderness.
• Current Version Information
  • APRSdos = 8.38
  • MacAPRS = 3.2.7
  • WinAPRS = 2.2.7
  • javAPRS= 1.2
  • APRSSA4= 0.9.22
• APRS Maps
  • Go to TAPR site to download APRS Dos maps (including Northwest APRS maps: NWMAPSxx.ZIP)
  • Go to TAPR site to download MacAPRS maps
  • Go to TAPR site to download WinAPRS maps
• Decoding Global Positioning System Sentences
  • RMC - Recommended minimum specific GPS/Transit data
  • RMC Sentence Format: $GPRMC,123519,A,4807.038,N,01131.324,E,000.0,276.9,150895,000.5,E*73
  • $GPRMC,HHMMSS,A,DDMM.MM,N,DDDMM.MM ,W,XXX.X,XXX.X,DDMMYY,XXX.X,E*XX
  • Decoded 1 2 3 4 5 6 7 8 9 10 11 12
    • 1. Time (UTC) : of fix
    • 2. Position valid (A=valid, V=invalid) :
    • 3. Latitude at UTC time (degrees and minutes)
    • 4. Latitude direction (N=north, S=south)
    • 5. Longitude at UTC time (degrees and minutes)
    • 6. Longitude direction (E=east, W=west)
    • 7. Speed over ground (knots)
    • 8. Course over ground or track (degrees, true)
    • 9. Date (day, month, year) : Date of fix
    • 10. Magnetic variation (degrees)
    • 11. Magnetic variation direction (E=east, W=west)
    • 12. Checksum
  • Garmin-45 RMC: $GPRMC,062428,A,3250.782,N,09645.682,W,000.0,360.0,310595,,*00
  • Tripmate RMC: $GPRMC,020438,A,3300.9990,N,09649.7490,W,53.549,181.3,240397,5.7,E*54
  • APRS processed RMC GPS fix: CS>APRS:@011714z3216.89N/10852.57Wu233/56./APRS/good RMC Fix
  • Points to note:
    • Processed APRS data is 2 decimal places or DDDMM.MM
    • Garmin RMC output is 3 decimal places or DDDMM.MMM
    • Tripmate RMC output is 4 decimal places or DDDMM.MMMM
    • The NMEA format is comma delimited so most software can process the different GPS data strings.
• Mic-E (Microphone Encoder)
  • The Mic-E is a nifty device about the size of a KPC-3 than connects between your VOICE radio and microphone, eliminating the need for a second tracking device and radio. When the microphone is UN-keyed, a very small packet (.03 seconds) containing GPS-derived position data is sent. On the RECEIVER side the audio is patched into RX on the TNC, and can be combined with a packet frequency, and passed on to APRS for decoding and plotting. Or you can use the Mic-E on the APRS frequency and set it to auto transmit at any rate, say each 30 seconds. This allows you to install a Mic-E in any vehicle equipped with a two-way radio, operating on any frequency, and then track the location of that vehicle whenever the mic is keyed/unkeyed.
  • A GPS-20 can be installed in the Mic-E, requiring an external antenna, or an external GPS, like the GPS-30, is available.
  • Mic-E's in various configurations are available now in partial kit form from TAPR, for about $170-400.
  • 
• APRS Mobile/GPS Operations
  • Remote Tracking... The GPS must have a data output providing RMC, GGA, or other sentence. This is fed into the TNC and is stored in a buffer until the transmit cycle. On a Kantronics TNC, the data pin is 3 and ground is 5. On the PacComm Handi Packet, data is on pin 2 and ground is 7. Check your TNC's manual for correct configuration. Wire the radio to the TNC according to your manual, and configure the TNC to transmit at least once per minute. The newer TNCs support multiple buffers and configurations, which can allow you to program different digi paths or transmit times. Once configured, power up the unit and allow the GPS time to lock on to the satellites. Based on a cold start GPS it may take 10 minutes to lock on and provide a current fix. A fellow ham built up several remote trackers for use in the Barstow-Vegas run last year.
  • Portable Tracker... I've built several mobile and portable trackers. One of my favorites has been a new configuration of GPS, TNC, and RADIO. This system includes the DeLorme TripMate GPS, PacComm HandiPacket or PicoPacket, and Radio Shack HTX-202. It's completely self-contained, including built-in battery power, or can be powered via a cigarette lighter adaptor and 12vdc. The system is very compact.
    
  • Mobile Operating... The setup for mobile ops is slightly different than described above, by adding a laptop computer (OK, you could use your desktop, but why?) and an APRS port splitter that periodically toggles between the computer and GPS to gather a current fix, which is then processed by the computer and sent to the radio for transmission. With this configuration you can watch your own progress, and update other stations running APRS. CAUTION.... IT IS DANGEROUS, AND ILLEGAL IN SOME STATES, TO HAVE A MONITOR, TV, OR COMPUTER IN VIEWING SITE OF THE DRIVER.
  • Global Positioning System...The GPS system is maininted by the U.S. Department of Defense and consists of 25 satellites in orbit around the earth. Positioning information is determined by a small receiver which measures the time in micro-seconds that it takes to receives the broadcast from between 1-8 satellites. By receiving the signal from at least four satellites, position information down to about 100 meters can be determined. Also, altitude information can be obtained from the system. In mobile situtations, speed and direction are also available. There are a number of commercial handheld GPS devices available, with a number of different features. Garmin makes a number of neat GPSs with lots of features for a very reasonable price. Trimble is another popular supplier of GPSs. Recently, DeLorme introduced the TripMate GPS. While this compact, inexpensive unit lacks a display for reading data, it is IDEAL for use with APRS, and has been efficiently integrated to the APRS program. It's small size means it can be easily hidden atop your vehicle, but it also works just fine sitting on the dash or rear shelf of your auto. The TripMate is included with DeLorme's Street Atlas CDROM version 4.0. There are a gazillion good reasons to own this package. To find out more, click on the graphic below.

  

  Pat Bunsold, WA6MHZ, San Diego Section Manager,  provided this summary for using the DeLorme TripMate with a Kantronics KPC-3: "Do the tricks by tying pins 2 & 3 together and modify the KPC-3 with R-48 and the 2 jumpers for bringing out power on pin 25 of the DB-25. Then put a 6v regulator inside the mating DB-25 connector to run power to the Tripmate on pin 9 of the DB-9 from the TripMate. Use a computer motherboard jumper to jumper the + pin to the center pin inside the TripMate and you're all set! " Furthermore, Pat added "There is no need to consider putting the TripMate outside the vehicle: For cars use the rear parcel shelf and for trucks use the front dashboard. Hide the TripMate inside an opaque plastic sack, or better yet, a fastfood bag and run the power cord along the window/shelf crack to hide it". Pat says he's had excellent results as compared to the hair tearing when he used the high current drain Trimble mushroom GPS.

• APRS Weather Station Operations
  • A number of low-priced "home" weather stations can be interfaced with APRS to report live and up to date weather information over an APRS network. The display appears as a blue dot. Peet Brothers offers the Ultimeter and Ultimeter II weather stations; Davis has the Wizard weather stations. Radio Shack and others are available as well. Prices start about $375 for a nice station that includes rainfall collecting and reporting.
  • A separate validation number is required to operate a WX station on APRSdos.
• APRS Direction Finding Operations
  • APRS can be used to track interfering signals on the radio, or zero in on the fox, by incorporating the Agrelo Engineering DFjr. The system consists of an antenna array, control module, and APRS interface. Your TNC, GPS, and computer all plug into the interface. A separate APRS DF validation number is required for use with APRSdos. The unit is simple to assemble. DF lines of bearing appear on the APRS screen. Triangulation can be easily accomplished with two or more DFjr equipped mobiles.
  • The DFjr can be semi-permanently mounted at a fixed site and report lines of bearing on any received frequency. A common scanner will work just fine.
  • The DFjr costs about $400, and is available from Agrelo Engineering.

  Here's the Agrelo Engineering DFjr control module.

• SoCA APRS WIDE Digipeaters:   (Click here)

• How to Join the APRS SIG hosted by TAPR
  • Send email to: listproc@tapr.org
  • Leave the subject line blank
  • In message body, type "subscribe aprssig (first name) (last name)
  • To unsubscribe, repeat above but change body to "unsubscribe aprssig"
• California APRS SIG Listserver
  • To join, email: admin@lists.monterey.edu, body: subscribe aprs FirstName Callsign
  • To leave: Same as above, but change "subscribe" to "unsubscribe"
  • To post: email:aprs@lists.monterey.edu
  • To learn more, email: admin@lists.monterey.edu, body:info aprs
• SCDCC Listserver
  • To join, email: majordomo@qth.net, body of message: subscribe scdcc (your email address)
  • To leave: Same as above, but change "subscribe" to "unsubscribe"
  • To post: email: scdcc@qth.net