08 APRS Messaging

APRS Article 8

September-October 2000

APRS Messaging

By Jeff Robbins

VE3JTR (Voice Call)

VA3JTR (APRS Call)

APRS is pretty cool. That is the reaction I keep getting whenever I finish talking about this hobby. Many of my listeners have seen the movie Enemy of the State, where Will Smith’s character was bugged by the government and using their elitist equipment, were able to follow his movements throughout the movie. While our APRS tracking units are not the size of dimes like in the movie, APRS does do the same thing for us. If you think about it, it is pretty cool. Another reaction I have heard from time to time is that APRS is about as exciting as watching paint dry. Well, if you restrict APRS to its original mandate, tracking stations on a map, than I can imagine it being quite boring. Fortunately, the authors of the various APRS utilities didn’t just stop with tracking and have continued to develop APRS into more than just icons on a map. Over the next few issues, I will be exploring some of the added features that have made APRS a well rounded, and useful addition to your shack.

We are communicators. After all, we got started in this hobby because we wanted to be able to communicate with others, over the airwaves. So naturally, one of the first additions to APRS was real time messaging within the network. APRS users can send one-line messages to each other, and the receiving station acknowledges receipt of the message. Hold on! It is true that I have previously stated that APRS uses unconnected packets to distribute information around the network, and no acknowledgements are used, unlike regular packet, which requires an acknowledgement for each packet received. This is the only exception to the rule. When a message is received that is specifically addressed to your station, your station will send out an acknowledgement so that the sending station can confirm receipt. WinAPRS has the ability to send out three types of messages, and each is handled a little differently be the sending and receiving stations.

MESSAGES are one-line text messages that are addressed to a specific station. When sending a new message, you will fill in the ‘To:’ box with the callsign of the destination station, along with any SSID, of course. WinAPRS will send the message out until it receives an acknowledgment, or, if no acknowledgment is received, the message times out. The timeout setting is adjustable, but is usually set to four attempts before quitting. When viewing your messages in the message list, your can see that initially your outgoing messages are coloured blue, indicating a queued message, and are changed to green when an acknowledgement is received indicated successful delivery. Shortcut Hint: In WinAPRS just hit F7 to bring up the message dialog box. When a message is received addressed to your station, the message list will automatically open and display the received message.

BULLETINS are short term, time critical messages. Bulletins are transmitted every twenty minutes for four hours, and then are retired. Bulletins might be used to disseminate important information, perhaps road conditions during a winter storm, for example. Information that you would like transmitted frequently, to ensure all stations receive the bulletin, but where the information will expire quickly, is a job for a bulletin. Click on the Bulletin button inside the message dialog to send a bulletin.

ANNOUNCEMENTS are longer-term messages that are not as sensitive to time requirements. Announcements are transmitted once an hour for four days. A good use for announcements might be to notify the network of club meetings, special event stations, or what ever else you can imagine. Click on the Announcement button inside the message dialog to send an announcement.

Sending messages using MacAPRS is very similar to WinAPRS. DosAPRS is easy to use as well, just press S and you will be prompted for a destination callsign. Enter the callsign, press ENTER, enter the message text, press ENTER, and your message is on its way. Sending bulletins and announcements requires entering another option in the To: field. Instead of a callsign, Bulletins are labeled BLT1 through BLT9, and Announcements are labeled BLTA through BLTZ.

BULLETIN GROUPS can be setup to send out information to a specific group of recipients. Lets use an example of an ARES Response Team. Perhaps many of the team members use APRS, and they choose it to distribute ARES information. Bulletins could be formatted and sent out to BLT1ARES1. The BLT is standard, followed by a numeral for a bulletin, or a character for an announcement. Immediately after, five spaces are allowed for a group name. Everyone in the network associated with the ARES Team could specify in their Bulletin Groups of Interest list the name ARES1, and when bulletins with that name are received, the station would announce the reception just like a message receipt. All kinds of interesting uses come to mind. Unfortunately, while the use of bulletin groups is detailed in the APRS Protocol Reference, I could not figure out how to establish a Bulletin Group of Interest List in WinAPRS. Perhaps it is on the list of To-Do Things for future versions!

VA3DRV visits QARC

The June meeting of the Quinte Amateur Radio Club (Belleville) included an informative presentation by Marc VA3DRV. I am sure every APRS Ham in Ontario has seen Marc’s transport truck heading up and down the Hwy. 401. Marc is one of the ambassadors of amateur radio, especially APRS. Members that attended the meeting had an opportunity to explore Marc’s rolling ham shack. Unfortunately, Wednesday nights are always reserved for my Fire Dept. practices, so I was unable to attend to meet Marc myself in person. On the APRS side, I do have one suggestion for you, Marc. The eighteen-wheeler icon you use is probably accurate most of the time. However, perhaps we should develop another icon with the trailer missing, so that we will know when you are running bob-tail! Cheers and 73, everyone, and we will be seeing you On The Map!