HANDHELD COMMUNICATIONS TEST VIA MIR Bob Bruninga, WB4APR ENS Chirs Morgan THE TEST: During the week of 2 June an impromptu test was conducted via the MIR Digipeater to demonstrate the capability for an Amateur Radio hand-held Satellite messaging system. Taking advantage of the thousands of Kenwood TH-D7 hand held radios with built-in TNC and APRS, the objective was to see how many operators were able to exchange data using only the 5 watt radio and rubber duck antenna. RESULTS: The results were enthusiastic. Almost everyone that tried was eventually successful in digipeating at least one packet via MIR on each pass. A total of 67 stations submitted reports showing over 190 different stations were logged. For this test, success was measured by the ability of a station to transmit his position, status and a short (few words) message. Thus the ability to use Amateur Satellites for two-way messaging between handheld data radios was aptly demonstrated. Using such simple UI Digipeaters in space could support hundreds of such stations per footprint per pass. (several hundred over the USA alone). Imagine the benefit to HAM radio and survivable communications if we had a few such UI Digipeating Satellites in space! APRS DATA RADIOS: For readers unfamiliar with the Kenwood THD7 APRS radio, it has a built in TNC and user interface so that you can capture and display the STATUS, POSITION and MESSAGES from as many as 40 other stations. It can send your own STATUS and position as well as single line messages up to 45 characters in length. This communications uses the APRS Mic-Encoder format so that these packets are typically less than a half second in length at 1200 baud. THey are transmitted in the unconnected or UI mode so that no acks are requred. When the HT does see its own packet digipeated, it displays "MY PACKET" so you can tell that it was successful. This is very valuable at reducing QRM on the uplink, since successful stations can then stop transmitting. The TH-D7 can transmit two types of packets: POSITION/STATUS - contains your LAT/LONG, and map ICON. ALso contains one of 7 pre-defined "comments" Also may contain up to 20 chars of STATUS MESSAGES - Any text up to 45 characters in length. Note that every APRS station will receive and display your POSITION/ STATUS, but MESSAGES are only captured by the receipient. For this reason and to vastly improve your chances of success via a space digipeater, stations were encouraged to send their traffic addressed as a BULLETIN to all, so that everyone could see the traffic. POWER and ANTENNAS: Although most people have not considered 5W as a viable power level to operate MIR, there are many advantages in the handheld scenario making it much more successful: 1) Lack of coax provides 3 dB average improvement on XMT & RCV 2) ABility to tilt antenna to match downlink polarity can gain 3 to 10 dB over fixed base station antennas at some times. 3) All stations were using the same power and rubber duck antenna thus getting equal chance moderated only by the ever changing satellite geometry. Sooner or later your geometry is optimum. 4) Only one or two packets were needed for "success" 5) Low power allowed operation without interferce to other PMS users TYPICAL PASS: Using the THD7, you typically would load your position and status and a brief message (bulletin) before the pass. THen on hearing the MIR packets, your display would begin flashing the calls, locations and bulletins of other stations heard. When you heard a silent gap in packets, you could hit the BCON button to force your own position/status packet. On being successful, by seeing your own packet digipeated, you could then bring up your message list and press the TRANSMIT button to force your longer BULLETIN message if desired. STATISTICS: Since the MIR digipeater shares the same radio with the BBS, and the BBS users are usualy running considerably higher power, then the lower power HT stations were only successfull during dead time between BBS packets. To consider the statistics of all packets on the downlink during a pass, the following data was recorded during three passes over the USA (MD) and Europe. Note, "DM" frames are "BUSY- REJECT" packets which just waste air-time). EUROPEAN PASS: 32 of 33 stations trying to log on (280 DM frames(80%)) BBS: 330 packets to transfer 27 useful lines of text = 8% success CNCT: 17 packets to transfer 1 useful line of text = 6% success UI: 2 packets to transfer 2 useful lines of text = 100% success USA PASS1: 4 of 15 users trying to log onto BBS (15 DM frames 19%) BBS: 54 pkts to transfer 10 useful lines of text = 18% success UI: 31 packets conveyed 26 useful text lines = 84% success USA PASS2: 4 of 16 users trying to use BBS (23 DM frames (15%) BBS: 98 pkts to convey 18 useful lines of text = 18% success CNCT: 29 pkts to convey 1 text line = 3% success UI: 28 pkts to convey 26 useful lines or text = 93% success The lower number of users on the USA passes were mostly due to the time being a weekday and the European pass was a nighttime or weekend pass.