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Digital Communications in the Amateur Services

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Digital Communications in the Amateur Services Digital communications in the amateur services Morse code: Earliest amateur digital system Since early 1900s, Morse used in amateur services and actively used today Speed 5-60 WPM, on/off keying Emission150HA1A (150HJ2A in SSB transmitter) Presently defined in ITU-T Rec F.1, Division B, but no longer used in public network ITU-T agreed to transfer responsibility to ITU-R ITU-R PDNR drafted to maintain Morse code Need for @ symbol: propose [AC] .--.-. Narrow band direct printing (NBDP) Radioteletype (RTTY) Introduced ~1947 using surplus TTYs Alphabet ITA-2 Rate 45 bauds Modulation 170 Hz FSK Emission 250HJ2B No error correction or detection Still used by amateurs as “chat” mode Packet Radio 300 Bd 1200 Bd Late 1970s: Began in Montreal, PQ, Canada Early 1980s: Vancouver, BC, Canada 1983: Standardized AX.25 protocol; ITU-T X.25 link layer, radio call signs, repeaters Adopted by some mobile and fixed service users Successful on VHF/UHF but poor tolerance for selective fading and collisions at HF AMTOR (ARQ) AMateur Teleprinting Over Radio 1980-1983: UK amateur Peter Martinez developed an amateur version of ITU-R Rec 476 Arrows show signal path from sender to receiver Cycle time limits distance to 20 000 km Also FEC Now obsolescent PACTOR 1991: Developed by German amateurs Hans-Peter Helfert et al to combine features of packet and TOR IA5 (ASCII) code using Huffman encoding FSK 200 Hz shift Emissions 340HJ2B 100 Bd, 440HJ2B 200 Bd (adaptive) Two stations exchange data and acknowledgement signals Cycle time limits distance to 20 000 km, long-path option 40 000 km Now obsolescent; replaced by PACTOR 2 PACTOR 2 Adaptive; modulation depends on link quality; 7 dB S/N better than PACTOR 375HJ2D emission Up to 700 bit/s throughput using Huffman encoding, run-length and pseudo-Markov compression Cycle time limits distance to 20 000 km, long-path option 40 000 km Used by United Nations Voice bandwidth data modems PACTOR 3 Clover 2000 5 200 bit/s max throughput 3 000 bit/s max throughput Emission 2K40J2D Emission 2K00J2D PSK31 1999: This and many other techniques use PC sound cards Most popular HF digital (chat) mode for amateurs 31 bit/s phase shift keying No error correction Emission 60H0J2B Spectrum display (amplitude/frequency) Waterfall display (time/frequency) Incoming and outgoing text also displayed on screen MFSK16 Multi-frequency shift keying, similar to Piccolo or Coquelet of the 1930s 16 carriers spaced 20 Hz; keyed at 20 Bd Intended for weak-signal work, robust Uses PC sound card No error correction WSJT: Weak Signal Communication Nobel prize winner Joe Taylor developed unique weak-signal software for meteor burst using FSK441 protocol (440 Bd) Later introduced JT44 which can decode steady signals 10 dB below the weakest Morse signals that can be copied by the human ear Digital voice (3 kHz DRM) November 22, 2002 first transatlantic (USA-France) amateur HF digital voice contact using a 3-kHz version of Digital Radio Mondiale (DRM), Rec ITU-R BS.1514 QPSK mode at 1200 bit/s produced "toll quality“ and 16- QAM mode at 2400 bits/s yielded noise-free “FM quality.” Demonstrated potential for simultaneous voice and data Stations used 100 W, directional antennas Digital voice AMBE/IMBE First digital voice system used in Digital voice modem the amateur service by two UK plugs into microphone amateurs and speaker connectors of SSB radio Same system used in Iridium, Automatically switches APCO Project 25 between analogue and digital signal Emission 2K80J2E Can capture slow-scan Special modems required now TV still images and convert to JPEG or fast- but future ones expected to be scan TV standard embedded in transceivers Digital amateur television DATV developed by amateurs at Bergische University Wuppertal, Germany 2 MHz bandwidth at 434 MHz, MPEG2 encoding, GMSK, QPSK or 8VSB modulation; 6 MHz at 1 255 MHz Some observations Amateurs continue to experiment with digital systems Personal computer sound card DSP engines permit software radio implementations Systems are somewhat adaptive – more to come.
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