Features and Technical Specifications of JT65
      ---------------------------------------------
                   Joe Taylor, K1JT

1  User Features

   1.1  Transmit/Receive period: 60 s
   1.2  User messages of three types:
          1. Call_1 + Call_2 + Grid
          2. Shorthand messages for RO, RRR, and 73
          3. Arbitrary text up to 13 characters
   1.3  Message averaging: continues without penalty when "OOO" is 
        added to message type 1
   1.4  Forward error correction (FEC) included in message types 1 and 3
   1.5  Automatic Frequency Control: corrects drifts up to 10 Hz/min
   1.6  Sensitivity: exceeds JT44 by at least 3 dB (see below)

2  Message Coding and Transmission

   2.1  User message source encoded to 72 bits
   2.2  FEC with RS(63,12,52) block code and 6-bit symbols
   2.3  9 x 7 interleaving of encoded symbols
   2.4  Convert to 6-bit Gray code
   2.5  64-ary continuous-phase FSK modulation
   2.6  Sync tone at 65th frequency in pseudo-random sequence

3  JT65: Reception and Decoding

   3.1  Time and frequency lock using sync tone and pseudo-random 
        sequence
   3.2  Automatic frequency control follows frequency drifts up to
        10 Hz/min.
   3.3  Noncoherent detection using 64-bin spectra
   3.4  Ratio threshold test marks symbol erasures
   3.5  Remove Gray code
   3.6  Remove interleaving
   3.7  Reed-Solomon decoding with Berlekamp-Massey errors-and-erasures
        algorithm
   3.8  AFC is aided by advance knowledge of "expected message"

4  Technical Specifications

   4.1   Duration of transmission, key down: 46.8 s
   4.2   User information, per transmission: 72 bits
   4.3   Total bits sent per transmission: 378 bits
   4.4   Modulation: 64-ary orthogonal FSK, continuous phase
   4.5   Demodulation: noncoherent power spectra
   4.6   Symbol size: 6 bits
   4.7   Symbol duration: 4096/11025 = 0.372 s
   4.8   Keying rate: 11025/4096 = 2.69 baud
   4.9   Channel bandwidth: 2.69 Hz
   4.10  Total occupied bandwidth: (64+3)*11025/4096 = 180 Hz
   4.11  Synchronizing: uses 65th tone (orthogonal to all others)
   4.12  Synchronizing vector: 63 symbols, pseudorandom pattern
   4.13  Total symbols per transmission: 126
   4.14  Data symbols per transmission: 63
   4.15  Sync symbols per transmission: 63
   4.16  Primary FEC code: Reed Solomon, RS(63,12,52)
   4.17  FEC code rate: 12/63 = 0.19
   4.18  Additional encoding: 7 x 9 interleaving and Gray code
   4.19  Decoding: Berlekamp-Massey algorithm, with erasures
   4.20  Source encoding of callsigns and grid locators: basic idea from
         Clark and Karn's EME-2000 paper
   4.21  Shorthand messages:
           1. Two tones in alternating sequence
           2. Tone duration: 16384/11025 = 1.49 s
           3. Tone separation: N*26.92 Hz, N=2,3,4

5  JT65: Sensitivity comparison with JT44, single transmission

   5.1  NB: Positive dB numbers mean that JT65 is better by stated amount
   5.2  Figures do not include source coding gain. Depending on message
        length, this can be up to 2.6 dB in favor of JT65
   5.3  AWGN channel      BER=0.01:   +3.6 dB
   5.4  AWGN channel      BER=0.001:  +4.5 dB
   5.5  Rayleigh channel  BER=0.01:   +9.7 dB
   5.6  Rayleigh channel  BER=0.001: +11.0 dB
   5.7  Shorthand messages: +5 to +7 dB, approximately