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@weca.org) In other articles I've described what The Automatic Position Reporting 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 sta- tions 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 on- ly situation when APRS uses anything other than UI packets. When you send a message in this manner, it will be sent via the same di- gipeater path as your position and ID packets. If your intended recipi- ent is someplace else, you can STILL send it there by specifying an al- ternate digipeater path, 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 WA2YSM-15,WB2ZII,WA2JNF-15,KB2EAR-1,K3ATI-11 to get to Southern New Jersey from Northern Westchester. To see which paths you've stored, press O(perations) D(igipath) L(ist). The main 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 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 (as of now, August 1999, it's 8.42) and the options the weather station has, you can get different kinds of information inclu- ding temperature, rainfall amounts (to the 1/100th inch) in the past hour and 24 hour periods, wind speed, direction and gusts and barometric pressure. By pressing W(eather) I(cons), or W(eather) D(isplay), you'll see a list of options to choose from. These have changed for the bet- ter) 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. When you want to send a specific packet (most often your position) you can do so by pressing X(mit) P(osition) [or S(tatus), M(essage), 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(pera- tions) F(ind) (what else!) command. If you want to see something really neat, try O(perations) R(eplay), and type in the callsign of a mobile station. What 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) use O(perations) Q(uery), f ollowed 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 a backup of this information, which it does by default. Next time you fire it up, APRS will reload this backup file. Every time you shut APRS down it'll save this file, replacing the previous copy. Be aware, though, that all of those packets are time-stamped, and any station's data 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.) One thing to remember when playing with APRS is that the best way to learn, as with anything else, is by doing. You can play with the com- mands 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. Usually the three-fingered-salute (Ctrl-Alt-Del) will get you out of it and you'll have to start over. So play with the thing. I mean, how do you think I learned all this about APRS stuff, by reading about it? 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 sug- gestion: 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. You can also purchase "Getting On Track with APRS", which was written by none other than Stan Horzepa (WA1LOU). It's available at many ham radio shops as well as your local hamfest. Or you can order it directly from the ARRL. Stan's book will walk you through much of what you'd like to know, in somewhat more detail than I can here. Mr. Horzepa is the au- thor of the "Digital Dimensions" column in QST magazine, and also runs the WA1LOU-15 digipeater 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 assist- ance 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 situa- tion can only improve, so come and join us on 144.390! 73 -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ FIGURING OUT THE BEST DIGIPEATER PATH FOR APRS PACKETS (or, Which Way Do They Go, George?) by Arte Booten, N2ZRC As with any packet networking, it depends on what can be heard by you and those that can actually hear you. You can get the equivalent of an MHEARD command showing you the paths stations around you are using & which stations you hear direct from the LISTS drop-down menu. See who these are. Hopefully, one of them will be a WIDE. Any APRS network relies on the majority of fixed stations having their TNC's DIGIpeat function turned on. Since APRS is an unconnected protocol, packet nodes (with few exceptions), which rely on connections and error-checking for data transfer, are counterproductive. APRS uti- lizes that DIGIpeat function by the use of GENERIC callsigns as a TNC's alias(es), most commonly RELAY and WIDE. There are various flavors of WIDE, all represented differently on the screens of different APRS versions. But first let me describe the function of RELAY in the APRS network, as this is a useful, but often misused, generic callsign. RELAY stations generally consist of your average "Joe Aperze" in order to allow low-power, low gain mobile and portable stations into the network. In many areas, most of these RELAYs are able to hit the nearest WIDE directly. This means that if you can hear and get digi'd by the nearest WIDE from a fixed location with reasonable consistency, you should AVOID THE USE OF RELAY because if a WIDE hears you, others probably can as well.. and they're probably also using the alias RELAY. This causes collisions as each of the RELAYs that hear you try to digipeat your packet at about the same instant. And your packet will probably die then and there. Now back to the various flavors of WIDE. The first is just that. It'll digipeat anything that specifically goes via its callsign as well as to the generic callsign WIDE, shown as a small green star in APRSDos. Sometimes, there's also a weather station associated with this DIGI, in which case APRSDos shows them as a green circle. Next comes WIDE-RELAY. These are TNC's that can have two aliases and digi packets addressed via RELAY, WIDE or its own callsign and show on APRSDos as big green stars. We also use WIDEs that use an alias of TRACE. Their firmware sup- ports the DIGI-SWAP function. When it DIGIs something addressed via one of its generic callsigns it changes that GENERIC callsign to that of its own in the VIA: field of that packet. This allows people to see how the network is propagating and makes selection of paths a bit easier. Those of us running APRSDos, WinMacAPRS and pocketAPRS see these as that large star with a T in the middle. The next type uses something the inventor of APRS (The Great Oracle of Glen Burnie) Bob Bruninga, WB4APR, first proposed several years ago to enhance unconnected networking via amateur packet radio and Kantro- nics recently picked up on. It uses a scheme Bob calls WIDEn-n. "N" is a number between 1 & 6. The first of these would represent the number of "hops" you want to take. The second of these numbers depends on how many times that packet has been digipeated by the time the last digi retransmitted it. It's set by the firmware in current Kantronics TNC's (but I understand that others *MAY* be coming out with it in the "near" future) and decrements one from that number on the packet it's heard, but hasn't yet DIGI'd. WIDEn-n TNC's can also be set for callsign substitution, as I described above. They have an N in the middle of the green star. The beauty of WIDEn-n is seen best in a network in which most, if not all, WIDEs in a given area have such firmware. In others, users of callsign substitution might consider shutting that feature off. Un- fortunately, not everybody that has a digi is USING Kantronics' stuff. And some of those that are aren't willing or able to change the chip. This pretty much describes the APRS network in my part of the woods. What's the best path? Look around. Who hears you. Who do they hear. And where do you want the packets to go? I suppose you'd like a nice, stable path from Montauk to Albany and Newark to Binghampton. Good luck. The path you need is there, if you can see anybody else on your screen. If a Green Star can hear you, then that's gonna be your starting point. From there, just follow the bouncing green stars. 73