Many of you have heard about a packet radio program called The Automatic Position Reporting System, (also called APRS.) It's a system which, unlike PBBS's, nodes and DX clusters, uses an unconnected protocol to transmit your exact position, a symbol denoting the type of station you're running and a brief comment about it. It also has direction finding capabilities and much more.
How does it work? In a 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. All of this information can be entered by hand, not a terribly hard job, or a Global Positioning System (GPS) receiver can be interfaced to provide location and speed information. With this information your station appears graphically on one of a series of maps on your monitor as would other stations that are being heard. Since this is an UNCONNECTED protocol, on air packets can be kept to a minimum.
Consider this: When you connect to a local packet station using standard AX.25, you send a connect request to that station, they acknowledge that packet, then send 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, thats OK because APRS will retransmit the same information packet using a decaying time delay. That means the second packet is sent eight seconds after the first, the third fifteen seconds later, the fourth thirty seconds later, the fifth a minute later, the sixth two minutes later etc. until it levels out and continues at once every twenty minutes. If the information in the message changes then the time cycle starts over again. This repeating of information makes your station show up on other people's maps with out ever needing to connect to them directly or send an ACK packet.
APRS uses four different kinds of digipeaters, which use the aliases RELAY, WIDE, ECHO and GATE. RELAY stations (the default setting) 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 and a GATE digipeats either from VHF to HF, HF to VHF or HF to HF. When setting up APRS for your location you'll set your digipeater path based on the situation at that location and where you want your information to go. When using APRS for keyboard to keyboard communications, which is the only mode in which ACK's are used in APRS, you can also set alternate digipeater paths. Not only does this direct your message via the shortest, most reliable route, but it also eliminates the digipeating of your conversation to all stations, far and wide.
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 severe weather situation is obvious. You can 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, by voice on a voice frequency or by keyboard in APRS, report their signals. Stations with beam antennas would report bearing and signal strength, stations using omni antennas report signal strength and antenna height and gain. This allows the APRS program to plot a coverage circle for these stations. The "fox" will usually be located where these circles converge or cross the lines of bearing. If you have one of the many "doppler" antenna systems it can also be used. All of the above methods are easily taken mobile.
If DXing is your thing, there's also a "DX mode" which also uses the unconnected protocol by simply monitoring the local DX cluster frequency with your APRS station. As new spots are posted, they appear on the map of the continent or the world 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 you have a 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 HT, 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. An other option for mobile or portable operation is to use a Mic Encoder. This small device allows you to send a very short, .3 of a second, data burst containing your APRS information at the tail end of your voice transmission on a voice channel. This method means you don't need a dedicated APRS radio or TNC or computer on board, just reuse the voice radio and frequency. A great help for public service events to be sure but not a good idea for every day use, for that equip your local repeater with a tnc (or a better choice, the Repeater node TNC, will keep out any data burst thats not from a Mic Encoder) that picks off the packet burst from the repeater receiver, sends it off onto the local APRS frequency and blocks the data burst from going out over the repeater transmitter. A full time vehicle tracking system that shares, politely at that, an existing voice repeater.
APRS was written to be able to run on just about any PC compatible computer from the latest Pentium Pro down to a lowly 8086. Maps are available from a large scale map of the whole world to extremely detailed street level maps. Users can make their own maps or customize the existing ones with ease. APRS is available to run on DOS, Windows, Mac and soon Linux machines. There's even a mail reflector about it to which you can subscribe, visit the TAPR internet site (www.tapr.org) to subscribe and find out much more about APRS, GPS, Mic Encoders and digital radio in general. The internet site at www.peel.com also is worth a visit to pick up maps, in particular Canadian maps.
It's lots of fun, has many potential ARES / RACES / SKYWARN / CANWARN / PUBLIC SERVICE uses and I'm sure you'll enjoy playing with it!
First things first you need to get the shareware program off the Internet. Using anonymous FTP, go to the following URL:
ftp://ftp.tapr.org/tapr/SIG/aprssig/files/
and then select either dosstuff/aprsdos or winstuff/winaprs directory and download the latest version of the program (the one with the highest number.) They're each roughly one megabyte.
If you use DOS and have PKZIP204g, put the APRS disk into the floppy drive of your choice (I'll call it drive A) then expand the APRS files (I'll call this APRSxxx.zip) by using the following commands on the hard drive of choice:
Don't forget to use that "-d" switch, which allows for the creation of the necessary subdirectories!
If you use Windows and WINZIP, double click on APRSxxx.zip, click on the expand button, tell it where you want it and follow the on screen directions.
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VERY IMPORTANT
IF YOU ARE USING A KANTRONICS TNC, OPEN THE FILE "INITTAPR.TNC"
(it's in the "APRS\SYSTEM" folder) AND, USING ANY TEXT VIEWER, CHANGE
THE LINE THAT SAYS "PAR 0" TO "PAR NONE". IF YOU DON'T DO THIS,
YOUR TNC WON'T UNDERSTAND ANYTHING THE PROGRAM WILL TELL IT!!
**********************************
Make sure your TNC is in Terminal or Command mode (whatever it's called by your manufacturer.) At the C:\> prompt, go to your chosen APRS folder and type "APRSxxx.exe". If you're using Windows, just double click on that file and "maximize" it. This brings you to the LOGO screen. Enter your callsign. 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 check the list for the appropriate maplist for your region. 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 or the right mouse button 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 press 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. Other places may be using the 144.390 Mhz simplex frequency or 145.790 Mhz simplex may be in use, try both but the Canadian standard is to use 144.390.
Look for stations whose symbol is a green star. THESE ARE THE WIDE AREA DIGIPEATERS! Is there one fairly close to you? If there is, press the D(igipath) key. If an asterisk (*) appears next to a callsign (hopefully that nearby WIDE) then you're hearing that station 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 call sign and ssid, if any. Follow this with a comma, then type in "WIDE". For example: "VE3MPC,WIDE" would be correct for Ottawa area, but the nearest WIDE to YOU is what YOU'RE looking for.
Next you want to set your Power Height Gain figures. Press I(nput) P(ower) and tell it how many watts you're using, your antenna's height above AVERAGE terrain (this is not the same as the height above you front yard, check a ARRL handbook in the repeater sections for the calculations) the gain in dBd and the antenna's directional pattern in degrees or 0 (zero) for an omni directional antenna.
Finally, set your Status 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. You can know watch the other stations pop up, and take the time to read the text files included with the APRS distributions.
So you're now probably telling yourself "OK, great. I've got these stations appearing on my screen. Now what do I do?"
The weather systems feature of APRS allows you to see various weather 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 and the options the weather station has, you can get different kinds of information including temperature, rainfall amounts (to the 1/100 inch) in the past hour and 24 hour periods, wind speed, direction and gusts and barometric pressure. By pressing W(eather), you'll see a list of options to choose from.
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. Press them again when you want to resume transmissions. 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) command. If you'd like to see something 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. Next time you fire it up, press F(iles) L(oad), then type BACKUP.BK, or whatever you'd like to call it. Every time you shut APRS down it saves a BACKUP.BK file, replacing the previous copy. Be aware, though, that all of those packets are timed , and any station that is reloaded from this backup that was heard more than two hours ago will "gray out" on the screen (APRS considers them to be inactive and makes room for more stations that way).
One thing to remember when playing APRS is that the best way to learn, as with anything else, is by doing. You can play with the commands as much as you want. You're not going to BREAK anything! About the worst thing that can happen is a lockup, and this is a rare thing. The three fingered salute (Ctrl-Alt-Del) will get you out of it and you'll just have to start over. So play with the thing, read the document files, then play some more.
Speaking of reading about it, yes you must It's 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 reread that paragraph for the fifth time and try's to 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. Most of the answers to your questions can be found there, sometimes buried deep and not quite as visible as you'd like.
We're all very excited about this program and think that "the more, the merrier" is the way to go. We've gotten a few "converts" in the last year and this situation can only improve, so come and join us on 144.390 simplex.