The Automatic Position Reporting System
An Overview and Introduction


by Arte Booten N2ZRC
(packet: N2ZRC@KB2VLX.#BRONX.NY.USA.NA)
(E-mail: N2ZRC@webspan.net)

Many of you have heard discussions about a packet radio pro-gram called The Automatic Position Reporting System, (also called APRS.) It's a system which, unlike PBBS's, nodes and DX clusters, uses an un-connected protocol to transmit your exact position, a symbol denoting the type of station you're running and a brief comment about it. It also uses direct keyboard-to-keyboard "chatting," has direction-finding capabilities and much more.

How does it work? In its most simplistic form you transmit a packet which contains your callsign, exact latitude and longitude, information on your transmitter's power, your antenna's height, gain and pattern as well as a brief comment of your choosing along with some symbols necessary to make the system work. With this information your station appears graphically on a map (actually, one in a series of many maps) on the monitor as would other stations that are on frequency. Since this is an
UNCONNECTED protocol, on-air packets can be kept to a minimum.

Consider this: When you connect to a local station using standard AX.25, you send a connect request to that station, they acknowledge that packet, then sends you a connected packet which you must then acknowledge. The same thing happens with EVERY packet you, or the other station, sends. With APRS you only send ONE packet to convey your information. If it's not received on the first transmission, APRS retransmits this information using a decaying time delay (that is, the second packet is sent fifteen seconds after the first, the third thirty seconds later, the fourth a minute later, the fifth two minutes later etc. until it levels out at a period of twenty minutes!) This makes more efficient use of the frequency.

APRS uses four different kinds of digipeaters, which use the aliases RELAY, WIDE, ECHO and GATE. RELAY stations (the default set- ting) are base stations used to digipeat low-power portable and mobile stations. WIDE stations will digipeat packets addressed either to their specific callsign or the generic WIDE to other VHF stations and WIDEs. An ECHO performs a similar function on HF. A GATE will digipeat from HF to VHF. When setting up APRS for your location you'll set your digi- peater path based on the situation at that QTH and where you want your information to go. For keyboard-to-keyboard communications (which are the only comms in which "ACK's" are used) you can also set alternate digipeater paths. Not only does this direct your message via the short- est possible route, but it also reduces QRM.

The program also interfaces with popular weather stations such as those made by Davis and Peet Brothers, thus allowing for real-time weather data which is available at the touch of a key. The potential for this during a SKYWARN situation is obvious. You'll get wind speed and direction, temperature, rainfall amounts by the hour and 24-hour period and, in some cases, barometric readings. Such weather data can also be entered manually if a station has the information but not the hardware.

There is also a Direction-Finding mode which can be used by stations with either a beam or omni antenna! When the "fox" transmits, stations can call, by voice (on another frequency!) or keyboard their beam headings and/or signal strength. Using the antenna gain figures for these stations, circles are drawn on the map. The "fox" will usu- ally be located where these circles converge. If you have one of the many "doppler" antenna systems they can also be used.

If DX-ing is your thing, there's also a "DX-mode" which also uses the UI protocol by simply monitoring the DX cluster frequency. As new spots are posted, they appear on the map with their callsign. Their location is based on the callsign prefix of the spot. Obviously, since you're not connected to the cluster, this isn't meant as a replacement to your normal AX.25 program, and you can't SEND messages, you can receive them (the program will flag yours and display them when asked.) It's just another tool for your county- or country-hunting efforts.

If, like me, you have a Global Positioning System (GPS) receiver with NMEA-0183 output this, too, can be utilized with amazing results! Your mobile or portable position can be regularly updated. Using such a "stand-alone tracker" you don't even need a computer. All you'd need is an H-T, TNC and GPS! Think about the possibilities for such a setup in something like a marathon, walkathon or even for someone shadowing an important official.

APRS was written to be able to run on just about any PC compat- ible computer from the latest Pentium Pro down to a lowly 8086. Heck, I know several people that use it with a Hewlett-Packard HP-200 palmtop! Maps are available from a large-scale map of the whole world to extreme- ly detailed street-level maps. There's even a mail-reflector about it to which you can subscribe. It's lots of fun, has many potential ARES / RACES / SKYWARN uses and I'm sure you'll enjoy playing with it!

SOME REALLY SIMPLE BASIC INSTRUCTIONS ON GETTING APRS ON THE AIR NOW


by Arte Booten N2ZRC
(packet: N2ZRC@KB2VLX.#BRONX.NY.USA.NA)
(E-mail: N2ZRC@webspan.net)

In this example I'm using the fictitious APRS version 9.99, which would be called "APRS999.zip." Substitute the appropriate file name for this.

If you don't use Windows, but have PKZIP204g, put APRS disk into the floppy drive of your choice (I'll call it drive A) then expand the APRS files by using the following commands on the hard drive of choice:

Make an appropriate directory MD APRS
Change to this directory CD \APRS
Switch to the A drive A:
Run PKUNZIP with directories PKUNZIP -d APRS999.zip C:

Don't forget to use that "-d" switch, which lets it create the necessary subdirectories.

If you use WINZIP, change to drive A and double-click on the APRS999.zip file, click expand button, tell it where you want it and follow onscreen directions.

Make sure your TNC is in Terminal or Command mode (whatever it's called by the manufacturer.) At the C:\> prompt, go to your chosen APRS folder and invoke "APRS999.exe". If you're using Windows, simply dou- ble-click on that folder. This brings you to the LOGO screen. Enter your callsign and ssid, if any. Tell it what kind of TNC you're using. Answer the other various questions. When you're done, the main map screen will appear.

Now press M(aplist) then C(hange), and tell it you want the map- list appropriate to your area [MAPLIST.EAS(t), .CEN(tral), SE(south- east), .MID(west) or .WES(t).] Use the arrows or mouse to bring the cursor to your approximate location (keep your eye on the upper left part of the screen which shows latitude/longitude of the cursor.) Then press HOME to center the screen on it. Use the PgDN key to zoom in a few screens and tweak the cursor to your EXACT QTH. You may have to zoom in to a very small scale to get the necessary resolution. Once the cursor is at the right spot hit the HOME key again.

Press I(nput) M(y) P(osition) and confirm your lat/long, choose a symbol for yourself, type in a brief comment, and verify it. Once you've pressed that "Y" you're essentially ready to go on the air. In it's most basic form, you're configured! Tune the radio to 144.39, hook it up and see what you can see. It might take a few minutes for other stations to appear (assuming there are some) but if you get a little impatient, try pressing O(perations) Q(uery) and give it a radius such as 64 to force position reports from others.

Look for stations whose symbol is a green star. THESE ARE THE WIDE DIGIPEATERS! Is there one fairly close to you? If there is, press the "D" key. If an asterisk (*) appears to the left side of a callsign (hopefully that of that nearby WIDE) then you're hearing it directly. Make a note of that nearby WIDE station's digipeater path.

Now you're going to set YOUR digipeater path. Press U(nproto). If you heard that WIDE station directly, enter it's callsign and ssid, if any. Follow this with a comma, then type in "WIDE". For example: "WA2JNF-4,WIDE" would be how I'd enter it here in The Bronx, but the nearest WIDE to YOU is what YOU'RE looking for.

Next you want to set your Power-Height-Gain figures. Press I(n- put) P(ower) and tell it how many watts you're using, your antenna's height above AVERAGE terrain (look at a topographical map of your area,) the gain in dBd and the antenna's directional pattern in degrees or 0 (zero)for an omnidirectional antenna.

Finally, set your Beacon Text by pressing I(nput) M(y) S(tatus) and typing in a short comment, different than the text you used for your Position Text earlier. At this point, you're about as far as you need to go for now.

I hope to see you all on my screen in the VERY near future. Look for me at cruise missile coordinates 4052.71N/07354.06W.

APRS: Using It
(or: Now that I've got it set up, how do I make it work for me?)


by Arte Booten N2ZRC
(packet: N2ZRC@KB2VLX.#BRONX.NY.USA.NA)
(E-mail: N2ZRC@webspan.net)
In other articles I've described what The Automatic Position Re- porting System is and how to get it set up on your computer and radio. So you're now probably telling yourself "OK, great. I've got these stations appearing on my screen. Now what do I do?"

One of the features in APRS is the ability to send what we call one-liners; that is, one-line messages from station to station either direct or by using digipeaters. From the main APRS screen press S(end), type the station's call and . Then type your message and another . You'll know when they got it when you receive an *ACK* which replaces the first five characters of your message. These one-liners are the only situation when APRS uses anything other than UI packets.

When you send a message in this manner it will be sent via the same digipeater path as your position and ID packets. If your intended reci- pient is someplace else you can STILL send it there (if you're using APRSDos, and soon, WinAPRS or MacAPRS) by specifying any of a dozen al- ternate digipeater paths which the program can store for you. If you press O(perations) D(igipath) S(ave), you'll be prompted to enter a two-letter code for that path via whatever path you choose, such as:

NJ VIA N2SF,WA2JNF-4,W2HOB

to get to Southern New Jersey from Westchester. To see the paths you've stored, press O(perations) D(igipath) L(ist). The prime purpose of these alternate paths is to keep the QRM to a minimum and to use the most direct and, sometimes, the only feasible path.

The weather systems feature of APRS allows you to see various wea- ther information in real-time which is transmitted by stations with a Peet Bros. or Davis Weather Station. Depending on which version of APRS you're using (as of now, January 2000, it's 8.46) and the options the wea- ther stations have, you can get different kinds of information including temperature, rainfall amounts (to the 1/100th inch) in the past hour and 24 hour periods, wind speed, direction and gusts and barometric pres- sure. By pressing W(eather), you'll see a list of options to choose from. These have changed for the better) in the last few versions, so I can't be specific.

If at any time you wish to cease transmitting without actually shutting down the program, simply touch C(ommands) X(mit). This will disable the timer within APRS. You will still send out whatever the TNC itself is set to transmit at the predetermined periods. When you want to send a specific packet (most often your position), you can do so by pressing X(mit) P(osition) [or B(eacon), M(essage), S(tatus), O(bject) or A(ll), as the case may be.]

In order to find a station on the screen, you can always use the O(perations) F(ind) (what else!) command. If you'd like to see some- thing really neat, try O(perations) R(eplay) with a mobile station. You'll see the station's track being replayed. To access your TNC you'd use O(perations) C(omms) T(NC) which leads you to a very basic terminal screen. To get stations to appear on your screen faster (within two or three minutes) you'd use O(perations) Q(uery), followed by a radius in miles from you.

Now that you've been on the air with APRS for a few hours, you don't necessarily want to wait for all those stations to reappear if, for some reason, you have to exit the program. No problem. When you shut down APRS by pressing Q(uit) Q(uit) , it asks you if you want to save a backup of this information, which it'll do by default. Next time you fire it up, you press F(iles) L(oad), then type BACKUP.BK . Every time you shut APRS down it'll save this file, replacing the pre- vious copy. Be aware, though, that all of those packets are timed, and any station in this backup that was heard more than two hours ago will "gray-out" (APRS considers them to be inactive and makes room for more stations that way.)

Speaking of reading about it, yes I did. It's all right there in the APRS distribution zip file. You can always read those files by pressing F1 F(iles) and typing in the name of the file you want to see. One suggestion: if you're a slow reader, press the down-arrow button once in a while as APRS seems to get impatient with you when it just sits there while you re-read that paragraph for the umpty-umph time and shoves you back into the program.

There are dozens of these readme files in the "README" folder. You can also see them (at your leisure and there for the printing) by using any old text editor. Many of the answers to your questions can be found there, sometimes buried deep and not quite as visible as you'd like.

In addition, Stan Horzepa (WA1LOU), who writes the Digital Dimen- sion column for QST Magazine, has written a book called "Getting On Track With APRS" which is available from the ARRL. By the way, Stan also operates a WIDE digipeater with the callsign WA1LOU-15 which is located in Wolcott CT.

I hope you enjoyed this series on APRS and hope to see you on the map in the near future. Whenever I see a new station on the screen I try to send them a one-liner welcoming them to APRS and offering live assistance and advice. Feel free to take advantage of this, or ask questions of any station on the air at that time. We're all very excited about this program and think that "the more, the merrier" is the way to go. We've gotten a lot of "converts" in the last few years and this situation can only improve so come and join us on 144.390! 73
TAWG would like to thank Arte Booten N2ZRC for his time and effort in putting this information together.

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