APRtrak.txt APRtrak APRtrak provides a mechanism for plotting the positions of stations and objects world wide based on both lat/long and grid square. It evolved from the APRS (Automatic Packet Reporting System) software which is a packet program for tracking mobiles using GPS units interfaced to standard AX.25 packet radios. The objective of APRtrak is to provide this same tracking and plotting capability for Spacecraft and satellite ground stations. Not only does APRtrak satisfy the inherrent curiosity that all amateur radio operators have about the locations of other stations, but it also helps newcomers to radio visualize the three dimensional and geographic aspects of satellite communications. APRtrak is designed to extract the most useful information for the largest number of users from the minimum number of packets. In this respects, it is unlike other packet programs, because it does not concentrate on the exchange of message text, but on position data. APRtrak avoids the overhead and complexity of a connected link by using the AX.25 unnumbered information (UI) packets. This mode is called UNPROTO for un-protocol packets. These packets are like beacons to everyone on frequency, instead of being addressed to individual stations. APRS scans these UI packets looking for position data or other useful information in every packet, and only needs one valid packet to plot a position. TELEMETRY: APRtrak has a simple telemetry decoding and display function for some very simple balloon and spacecraft payloads. It can display 5 analog channels and 5 digital bits of information. The primary advantage is that the channel definitions and equations can be distributed over the air, so that new software is not required for each different payload. An exception is for the SPRE payload scheduled for launch in Dec 95 which has been hard coded. See SPRE.txt. A single chip TELEMETRY/TNC has been designed by N3MIM which generates AX.25 audio packets with 4 analog channels and 5 digital bits. It makes a great match-box sized balloon payload. THE SHUTTLE AMATEUR RADIO EXPERIMENT (SAREX): The oginal SAREX packet robot was designed in the mid 1980's when most stations were still using dumb terminals with their TNC's. The robot provided unique serial numbers to each station that connected with the shuttle, but five successful and successive packets were required for success. Although hundreds of stations were successful, more than three times as many showed up in the HEARD log as having at least gotten one CONNECT-REQUEST packet through. Thousands more had probably tried. APRtrak was designed to take advantage of single packets to not only permit a greater success rate, but also to provide a more visually rewarding image of the spacecraft, orbit, and ground station geometry. Since shorter packets result in success of more stations, the complete position report is compressed into the TO address of all uplinked packets using the Maidenhead Grid Square system. These grid squares are only 6 characters but provide a location anywhere on earth to about the nearest 2 miles. These position reports then are just as short as a CONNECT-REQUESTs, provide much more information, and only required one packet for success! To demonstrate the effect of having SAREX relay these position reports, use the FILE-REPLAY command to replay the SHUTTLE.HST file and watch the contacts appear as the shuttle moves across the country. You may enhance the demonstration by selecting to see only the Shuttle, STS-99, or by turning off CALLS to reduce the clutter of callsigns on the display. Obviously, in this SHUTTLE.hst file, I assumed that the Shuttle had its TNC connected to a GPS navigation receiver so that it was also beaconing its position once per minute. APRtrak DISPLAYS: Obviously the map is the most important display screen, but APRtrak has several other screens for presenting other information about all packets that it hears as follows: LATEST - The latest UI frame received from each station. POSITIONS - Lists the positions of each station. MESSAGES - Single line messages to/from other stations. BULLETINS - This screen captures all BULLETINS. TRAFFIC - Shows the last 23 lines of messages heard. ALL LOG - Time sequenced log of every new beacon or message. HEARD LOG - Number of packets heard per station per hour. DIGIPTRS - Displays the packet headers and digipeaters used TELEMETRY - Displays 5 analog and 5 digital bit channels WHERE - Displays the predicted positions of up to 9 satellites AZ/EL (Z) - Shows your antenna's view of the sky STATION TRACKING. Although APRtrak was designed to track spacecraft and ground station position reports, it can also track any station, fixed or mobile that is transmitting its position via packet using the APRS protocols. Further provision is made for transmitting the location of objects on one station's screen to every one else's screen. This feature can be used by one station to uplink the position of an artic polar expedition, or ships at sea for example. GRID SQUARES: Because of the ambiguity of a grid-square position report, APRS will not display a 4 or 6 digit gridsquare report on map ranges less than 128 and 8 miles respectively. Stations reported in the same grid square are randomly offset to avoid cluttering of callsigns on top of each other in the same grid square. The P-list is annotated to indicate that the position is approximate. The big advantage of grid squares is their short length of 6 characters vice seventeen for lat/long. You may use the OPS-FIND command to locate any grid square on the map. PROTOCOL - Since the objective of the APRS protocols are the rapid dissemination of real-time information using packet UI frames, a fundamental precept is that old information is less important than new information. All NEW beacons, position reports, messages and display graphics are redundantly transmitted but at a longer and longer repition rate. Each new beacon is transmitted immediately, then 20 seconds later. After every transmission, the period is doubled. After ten minutes only six packets have been transmitted. From then on, only 1 packet every 10 minutes is transmitted. All transmissions can be turned off using the CONTROLS-XMT command. But a transmission can be forced at any time by hitting the X key. For details on the APRS raw packet formats see PROTOCOL.txt. COMMANDS: In most cases the keyboard is always active awaiting any of the many single key commands. Many commands bring up additional menus on the bottom of the screen. Note that APRS processing of packets on the air is continuous EXCEPT while waiting for the user response to a BOXED prompt. Commands fall in to 3 categories: SCREENS: The Space Bar will always re-draw the map screen and the page up/dn keys can zoom the map centered on the position of the cursor. You may save 4 special maps under the hot keys of 1,3,5,7 and 9. All of the other displays screens are called up by the letter key associated with their first letter. Use alt-T to call up the TELEMETRY screen. SUB-MENUS: F1- Help - Select from a MENU of HELP commands C -Controls - Display a one line status of all control states F -FILES Menu - For Loading/Saving files, or Replaying tracks I -Input cmds - Input posits, or add OBJects to map O - OPERATIONS - Several commands for normal operations M - MAP Menu - Functions dealing with maps MESSAGES: R - READ - Displays your incomming and outgoing messages S - Send - Sends traffic to a station E - Erase - Erases outgoing traffic lines K - Kill - Kills incomming traffic lines T - Traffic - Displays msg traffic between other stations ANTENNA AZ/EL SCREEN: The AZ/EL screen is a new screen which shows your antenna's eye view of the sky. You may move the cursor and zoom into any area of the sky. The position of the satellites are shown in real time and their paths can be shown by pressing the alt-F key for FAST mode. Use the INPUT-BEAM-heading command to enter the present position of your antennas. Enter the Beamwidth of your VHF and UHF antennas when you first configure APRtrak on startup. To customize the horizon to your backyard, edit the SYSTEM\HORIZON.dat file using a simple DOS editor. The format is described in the HORIZON.DAT file... Obviously, this horizon will only show up if the map screen is centered on your house. Otherwise, a random horizon will be drawn. DEMONSTRATION FILE: To see how APRtrak can display meaningful packet position reports in a number of different applications, use FILES-LOAD to load the file called VHF.BK. This file contains all the local stations on the local APRS frequency in the Washington DC area. To see the tracking of the GPS equiped Army/Navy game football run, load the file named FBALL.BK and replay the file named FBALL.HST and select to see only FBALL, or CHASE1. To see the Marine Corps marathon event, load MARATHON.BK and replay the MARTHON.HST file. See Details in README.TRK. HOOKING STATIONS: The cursor can be moved to select any station on the map screens using the arrow keys. When near any station symbol, the ENTER key will "hook" the station. Detail information on that station will be displayed on the bottom of the screen. Alternatively, use the + and -keys to step through each station one by one. You may also use the cursor on the P or L-list to hook a station or object. Once hooked, several functions may be performed: ALL BCNS- The A key will list all beacons from that station. MOVE - Move cursor and press the Insert key. DELETE - performed by hitting the D key. UPLINK - transmit the object to all other stations on the net KILL - kill the object from all displays in the network ALARM - You will be alerted if that station ever moves. TRACK - APRS will always center display on selected station #MARK - Mark special stations so that only these stations will show on the map when # is used instead of SPACE BAR for drawing a map. If * is pressed, all symbols will be shown on the map, but only the marked symbols (#) will show callsigns. The hook function also works on the LATEST and POSITION display lists by using the up/down arrow keys. If a position exists, hitting the HOME key will display the map screen with that station centered on the display. The G or GO key will go to YOUR station or if a station is marked for TRACKING on the P-LIST, then it will go to that station. REPLAY: The positions of any moving station can be replayed either from memory or from a file. Tracks are kept in on-line memory until 150 have been saved, and then are saved to a HISTORY file. During REPLAY, use the Calls command to toggle on and off the display of callsigns, and use the HOME and page keys to center and zoom the map display if the mobile station moves off the screen. During replay, use these commands: C - CALLsigns on/off HOME - Homes map to presently displayed station SPACE - Redraws the present map to remove track clutter F - Faster. Speeds up playback G - Overlays Civil Air Patrol Search and Rescue grids M - Medium replay speed P - Pause S - Slow. Slows down playback Q - Quit playback. PgUp/PgDn - Zoom in and out FILES: All APRtrak files are retained in five different sub- directories of BAKS, LOGS, HSTS, SYSTEM and README. There are several other files used by the system: MAPLIST.APR - Directory of all map files available to APRtrak BACKUP .BK - Backup of system every time program is quit. This file is overwritten every time the program is quit. It can be reloaded by simply indicating the letter B for a filename. MAPFIX...EXE - A map editing program for fixing or making maps. SYSTEM (DIR) - Contains the following required files IintTAPR.TNC - TNC setup parameters ( or InitAEA.TNC ) RESTORE.TNC - TNC commands to restore TNC after quiting CAPGRIDS.DAT - Civil Air Patrol Search-&-Rescue grids DXCALLS.DAT - Callsign prefix-to-LAT/LONG database XXXXxxx.SYS - Brief files for APRS internal screens HORIZON.DAT - Contains your horizon profile APRtrak OPERATIONS: APRtrak will always monitor the channel and plot any packets or positions heard. It will put POSITS on the P-LIST, APRS formatted Telemetry on the TELEMETRY page, and all other UI frames on the LATEST list. The ALL list will keep a chronology of all new packets and peridoically save them to the LOGS directory. Unlike the original APRS software, APRtrak will ignore terrestrial POSITS from stations that are using more than one digipeater. The track history of all positions will periodically be saved to the HSTS directory. There are two TRANSMIT operating modes for APRtrack. The nominal mode only transmits your position about once every 10 minutes. This position report is your exact LAT/LONG location and posiiton comments. It allows all stations on frequency within range of each other, to see who else is nearby. The other mode is SPACE mode specifically designed to transmit a minimum length grid- square report via a spacecraft transponder. In space mode, APRtrak places your GridSquare in the TO address of your TNC by using the UNPROTO command of UNPROTO GRIDSQ via XXXXX. Where XXXXX is the callsign of the satellite or spacecraft digipeater. If APRtrak sees your packet digipeated by the spacecraft, it will beep several times and display a CONGRAT'S message. To imporve your chances for getting a packet through the spacecraft, you may force a transmission of your GridSquare BEACON each time your press the XMT-BEACON command. A timer prevents you from sending an more than one packet every 8 seconds. Also in SPACE mode, APRtrak will automatically increase its beacon rate when ever it hears packets from the designated spacecraft digipeater. It does this by resetting the normal decaying BEACON period timers to minimum. This results in several packets over the next few minutes, but, as usual, the period between each packet doubles. To minimize QRM, any APRtrak station that sees itw own BEACON digipeated by the spacecraft will immediately reset its beacon timer to 4 minutes, since there is no need for that station to continue to transmit again until later in the pass to cover a different geographical footprint. OPERATING TIPS VIA DIGIPEATING SPACECRAFT: First, be sure that APRS position reporting is being authorized via the particular spacecraft. To have a good chance of being seen via the SPACE digipeater and to minimize unnecessary QRM, use the following procedures. Even under worst case scenarios, APRS stations will still generate fewer packets than other stations attempting to CONNECT to the spacecraft! * Set UNPROTO VIA the Space DIgipeater (W5RRR) * Set alt-SETUP-MODES-SPACE which makes your posit as short as possible and also opens up APRtrak to parse all OTHER packets instead of just APRS packets. Your station will be "armed" to reset its beacon timers to minimum as soon as it hears packets from the space digipeater. * Make your BCN text as short as possible, or none at all. * Use X command to force a transmission as desired * Use the VIEW screen so you can VIEW all packets on a full screen * Use your lowest 2m antenna (preferably on the ground). This minimizes any QRM to your receiver from other local uplink stations, and also minimizes your QRM to them. A ground level antenna should work perfectly well, since it can still see the sky, and the SPACECRAFT is so far away on the horizon and has such high doppler that you will NOT make it anyway at elevations below 20 degrees or so. If stations are still trying to connect to the spacecraft, you should put the CONTROLS-MCOM to ON so that you will also monitor all of the DISCONNECT-BUSY protocol packets being sent by the spacecraft. With MCOM ON, APRtrak will collect ALL packets (even dupes) to the ALL-LIST so you can see everyone involved in the pass. THe L and P-LISTS will still only accumulate UI packets. UNATTENDED OPERATION: If you use a low antenna as described above and leave APRtrak unattended, you should capture all POSITS digipeated by the spacecraft. Your station will be transmitting only one BCN and POSIT about once every 15 minutes. This is less than one-half of one percent (0.5%) of the number of packets generated by other stations trying to connect to the spacecraft. Of course your chances are similarly diminished, but its only fair for unattended stations not to QRM manned stations. If you set SPACE mode, then your station will come to life when the spacecraft is heard. If this idea catches on, then maybe all of those other stations will STOP trying to CONNECT to the spacecraft and join us! That would be a net REDUCTION in QRM on the uplink! Imagine the fun that the cosmonauts and astronauts will have if they carry a lap-top computer so they can see everyone on their maps!