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Text File | 1994-09-28 | 14.2 KB | 245 lines

PROTOCOL.txt 6.0 APRS ON-AIR PROTOCOL or FORMATS FOR USING APRS WITH DUMB TERMINALS Since most of the features of APRS can be used even if a station is not running the APRS software, this file describes the exact APRS formats so that they can be manually entered from dumb packet stations. This might often be the case from lightweight portable packet stations. Frequently the need for the map display is NOT out in the field where the portable packet stations are, but at the headquarters, or net control point. The following paragraphs suggest ways to use dumb terminals or non-PC computers and TNC's in an APRS network. All APRS communication is done using UI frames. UI frames are transmitted with all the error detection capability of standard packets, but they are not automatically acknowledged. The only disadvantage is that if a collision occurs or there is interference on the channel, the UI frame is not automatically retransmitted. In APRS this is not a problem because all information is redundantly transmitted in an effecient manner. UI frames can be transmitted easily from a TNC in two ways. First, by loading the TNC Beacon Text with a desired message, the beacon is repeatedly transmitted as a UI frame. The period of retransmission is set using the B parameter. Most standard TAPR-2 TNC's use 10 second increments so that a B_E_6 actually results in a beacon once every minute. A value of 60 is once every ten minutes. In Kantronics TNC's, 1= 1 Minute and so on. BText is often used in an APRS network to broadcast a one-line message to all stations. NOTE, that the APRS BText is generated internally in the APRS software and the TNC BText is not used while APRS is running. The second way to send UI frames is to enter CONVERSE mode directly from the cmd: mode without first establishing a connection. This is done simply by using either the CONV or K command. In this mode you specify your digipeater path by using the UNPROTO command. Once in UNPROTO CONVERSE, everything you type is still transmitted as normal AX.25 packets, except that lines are only transmitted once and acknowledgments do not exist. As long as you do not experience a collision, these UNPROTO packets are just as good as the connected protocol and are very effective at broadcasting information to many other stations at once. TO ADDRESS: One caution; since APRS operates in a broadcast fashion and does not use a connected protocol, the TO ADDRESS is not required. To help ignore non-APRS traffic which might also be on the channel, APRS stations use the TO ADDRESS field as a type of filter. APRS will only recognize UI frames transmitted to the broadcast addresses of ID, CQ, QST, BEACON, MAIL, SKYWRN, ,GPS, DFNET, SPCL and APRS. All other packets are ignored. For this reason, you must place one of these addresses in the TO ADDRESS field in your UNPROTO command. APRS does have the CONTORLS-OTHER command to over-ride this filter temporarily. NEW in version 6.0, is the alt-IGNORE command. This command turns off all of the above acceptible TO calls and will only accept packets addressed TO: SPCL. Similarly, these stations all transmit using the UNPROTO path of SPCL via XXXX... This makes it easy for a sub-group of APRS users to operate a special event on the same frequency as other APRS users, but to not be encumbered with all of their traffic. APRS FORMATS: Using either the BText or UNPROTO CONVERSE methods noted above, APRS reports can be transmitted manually from any TNC and dumb terminal. To transmit a report repetatively, enter it as a Beacon Text. To report it once, simply type it in the UNPROTO CONVERSE mode and hit the ENTER key. The following formats must be used exactly to have the desired effect at an APRS station. Abbreviations are D for degrees (or DAY), M for minutes (Both lat/long and time), h for hundredths (or Hours), N for North and W for West. The delimiter following the Longitude is used to indicate the type of APRS symbol to be displayed (shown here as a $). See the SYMBOLS.txt file. POSITION REPORT: To report the position LAT/LONG of your station you may either use the abbreviated format for a fixed station or the longer format for a mobile that includes the time of the position and an optional course, speed, and comments. If the symbol for a Triangle is used (\) then APRS assumes the report is a DF line of bearing for direction finding. To be compatible wiht TheNET node ID frames, the fixed format (starting with !) can occur anywhere in the BText. FIXED: ... !DDMM.hhN/DDDMM.hhW$comments... MOBILE: @DDHHMM/DDMM.hhN/DDDMM.hhW$CSE/SPD/comments... DF: @DDHHMM/DDMM.hhN/DDDMM.hhW\CSE/SPD/BRG/90Q/Comments ( Q=quality) GRDSQR: [XXnnyy]comments to end of line [XXnn]comments to end of line POWER: ..........................$PHGabcd... (Power,ant/height/Gain. See) (format below for digi's) OMNI-DF: ..........................\DFSxbcd... (Same as PHG, but x=sig str) .......z............................. (indicates Zulu date-time) TNC: /DDHHMM.............................. (If the leading symbol is a ) (/ instead of an @, then the) (packet is NOT generated by ) (APRS software, but usually ) (by a dumb terminal or TNC. ) (The Date-Time indicates ) (when APRS was last running ) POWER-HEIGHT-GAIN: This optional field replaces the CSE/SPD fields with a report of transmitter power, antenna height-above-average-terain and their antenna gain. With this information, APRS can plot communication range circles around all stations. This reporting capability should be an excellent tool for all TNC's not just those used for APRS, such as for BBS's and NODES. The following details the format to be used in the BText of a TNC dedicated as an APRS digipeater: !DDMM.mmN/DDDMM.mmW#PHG5360/WIDE...(identifying comments)... | | | | |||| |_____ makes station show up green | | | | ||||________ Omni (Direction of max gain) | | | | |||_________ Ant gain in dB | | | | ||__________ Height = log2(HAAT/10) LAT LONG | | |___________ Power = SQR(P) | |_____________ Power-Height-Gain identifier * |_______________ # is symbol for digipeater As you can see by the integers in the Pwr string, there are only 10 possible values for each of these fields as follows: DIGITS 0 1 2 3 4 5 6 7 8 9 Equation ------------------------------------------------------------------- POWER 0, 1, 4, 9, 16, 25, 36, 49, 64, 81 watts SQR(P) HEIGHT 10,20,40, 80,160,320,640,1280,2560,5120 feet LOG2(H/10) GAIN 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 dB DIR 0,45,90,135,180,225,270, 315, 360, . deg (D/45) The DIRECTIVITY field offsets the PHG circle by one third in the indicated direction. This means a front to back range of 2 to 1. OMNI-SIGNAL-STRENGTH DIRECTION FINDING REPORT: Obviously, since APRS can plot effective communication range circles around all stations, it was easy to add the capability to localize hidden transmitters by simply plotting the overlapping signal strength contours of all stations hearing the transmitter. In this instance, the PHG format identifier is replaced with DFS to indicate DF Signal strength, and the trans- mitter power field is replaced with the relative signal strength on an arbitrary scale of 0 to 9. The following beacon would represent a weak signal heard on an antenna with 3 dB gain at 40 feet: @141923/3859,11N/07629.23W\DFS2230/comments Although the backslash (DF) station symbol was used, this report will work no matter what the station symbol. Please note that 0 should only be used to indicate NO SIGNAL AT ALL! If the signal is even barely discernable, a 1 should be used. This is beacuse APRS uses the 0 signal level to draw circles where the transmitter is KNOWN NOT to be. WEATHER REPORT: APRS recognizes the underline symbol character to indicate that the report contains wind direction and speed information. This plots the station in dark blue and prevents APRS from assuming it is a moving mobile station. The remainder of the comment line can contain any other pertinent weather information. APRS has an optional automatic Home weather station interface for the Ultimeter-II which automatically inserts your weather conditions into your Posit report. It includes the optional Temp and Rain fields. @DDHHMM/DDMM.hhN/DDDMM.hhW_CSE/SPD/T073/R00/WxStn (auto) Dxxx/Pxx/Bxxx other optional fields for DewPt, Participation accumulation, and BaroPressure The R field is tenths of an inch of rain in the LAST HOUR The P field is tenths of an inch of rain in the LAST 24 HOURS OBJECT POSITION: To report the position of something other than your own station, the same format for a mobile object is used but it is preceeded with a nine digit object name. For shorter names, the 9 character field must be padded with spaces: OBJECT___@DDHHMM/DDMM.hhN/DDDMM.hhW$CSE/SPD/comments... BROADCAST: Simply send anything. If you are using your TNC BText to repeatedly send the same message, it is preferred to include the day and time that you entered the the BText in the text so that recepients can tell how old the information is. @DDHHMM/comments... MESSAGE: To direct a specific message to a specific station and have his bell ring and the message instantly flashed on his screen, use the following format, again padding the addressee call with spaces to a total of nine characters followed by a colon: W3XYZ____:one line message text......{3 (the {3 is the line counter) His station will acknowledge receipt with a responding message to you with only the letters ACK3 in the message. MSG ACK: If an APRS station sends you a message line, it will be repeated over and over until you send a responding ack. To send an ack to station W3XYZ, simply enter his call padded to nine spaces and a colon followed by the letters ACK# where the # is the line number tacked onto the end of his message line with a ({). W3XYZ____:ack3 BULLETINS: Each station can also send a multiple line BULLETIN to ALL stations by simply sending multiple single line messages to the special call signs of BLN1, BLN2, ... BLN#. All APRS stations collect all such BLN# messages and sort them onto the special BULLETINS page. They are also sorted by originators call, so that many stations can have BULLETINS flying at the same time. You may change any BLN# line at anytime, and all receiving stations will simply over-write the line with the latest line. DUMB PACKET TERMINAL DF REPORTS: Non APRS packet stations can also automatically report their lines of bearing into the system by simply entering a beacon text in the APRS format with their line of bearing. BText: !DDMM.xxN/DDDMM.xxW\000/000/BRG/N0Q/DF report... Where: DDMM.xxN is Latitude, DDDMM.xxW is Longitude \ (Backslash indicates a Triangle symbol for DFing) BRG is the DF bearing in degrees True N0Q is a Quality indicator where Q is a quality value (1-8) and N is an optional Number of HITS indicator. If N is 0, then it means nothing. Values from 1 to 8 give an indication of the number of hits per period relative to the length of the time period. So 8 means 100% of all samples possible, got a hit. The N is not processed, but is just another indicator from the automatic DF units. By entering a 9 as the HIT indicator, you can indicate to other users that your report is manual. USING AND DISPLAYING POSITION INFORMATION. If all manual stations in an APRS system carry a pre-printed map of the exercise or event area, not only can they easily determine their own location for reporting, but they can also plot the location of other stations and objects. Usually, you do not need the high technology of a GPS or LORAN receiver to know where you are. Most people can find themselves on a map and read the coordinates. Then they simply type them in to their BText and in a few minutes, everyone on the net can see their exact location. Similarly, by monitoring all of the APRS beacons going back and forth, the dumb terminal user can still be equally well informed of whats going on. DIGIPEATERS, NODES, BBS's AND ALL OTHER PACKET STATIONS: Since APRS is a generalized position displaying tool, EVERY Packet TNC in the country that is permanently on the air, and that also transmits a periodic ID beacon, should be reporting its position in that ID beacon! This way, stations monitoring can quickly see a geographical plot of the network. If you want to keep the exact location of your transmitter ambiguous, then use the GRID-SQUARE format, and your position will be ambiguous to a few miles, but stations can still see that you are on the air. If you have special formats for your BEACONS that contain variable information, then APRS is perfect for grabbing that information and making it available to users...