From 140be15ccece5566d4149187a4798579288be613 Mon Sep 17 00:00:00 2001 From: Joe Taylor Date: Thu, 28 Apr 2016 18:59:34 +0000 Subject: [PATCH] Starting to fill in the "Protocol Specifications" section of User Guide. git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6657 ab8295b8-cf94-4d9e-aec4-7959e3be5d79 --- doc/user_guide/en/protocols.adoc | 58 +++++++++++++++++++++++++++++++- 1 file changed, 57 insertions(+), 1 deletion(-) diff --git a/doc/user_guide/en/protocols.adoc b/doc/user_guide/en/protocols.adoc index 33d5a4b02..25d31845c 100644 --- a/doc/user_guide/en/protocols.adoc +++ b/doc/user_guide/en/protocols.adoc @@ -90,7 +90,7 @@ Hz, the inverse of the symbol duration. The total occupied bandwidth is 9 × 1.736 = 15.6 Hz. [[PROTOCOL_SUMMARY]] -=== Summary +=== Comparison of Slow Modes Frequency spacing between tones, total occupied bandwidth, and approximate decoding thresholds are given for the various submodes of @@ -135,3 +135,59 @@ JT9 is an order of magnitude better than JT65 in spectral efficiency. On a busy HF band, the conventional 2-kHz-wide JT65 sub-band is often filled with overlapping signals. Ten times as many JT9 signals can fit into the same frequency range, without collisions. + +=== ISCAT + +ISCAT messages are free-form, up to 28 characters in length. +Modulation is 42-tone frequency-shift keying at 11025 / 512 = 21.533 +baud (ISCAT-A), or 11025 / 256 = 43.066 baud (ISCAT-B). Tone +frequencies are spaced by an amount in Hz equal to the baud rate. The +available character set is + +---- + 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ /.?@- +---- + +Transmissions consist of sequences of 24 symbols: a synchronizing +pattern of four symbols at tone numbers 0, 1, 3, and 2, followed by +two symbols with tone number corresponding to the message length, and +finally 18 symbols conveying the user's message, sent repeatedly +character by character. The message always starts with +@+, the +beginning-of-message symbol, which is not displayed to the user. The +sync pattern and message-length indicator have a fixed repetition +period, recurring every 24 symbols. Message information occurs +periodically within the 18 symbol positions set aside for its use, +repeating at its own natural length. + +For example, consider the user message +CQ WA9XYZ+. Including the +beginning-of-message symbol +@+, the message is 10 characters long. +Using the character sequence displayed above to indicate tone numbers, +the transmitted message will therefore start out as shown in the first +line below: + +---- + 0132AA@CQ WA9XYZ@CQ WA9X0132AAYZ@CQ WA9XYZ@CQ W0132AAA9X ... + sync## sync## sync## +---- + +Note that the first six symbols (four for sync, two for message +length) repeat every 24 symbols. Within the 18 information-carrying +symbols in each 24, the user message +@CQ WA9XYZ+ repeats at its own +natural length, 10 characters. The resulting sequence is extended as +many times as will fit into a Tx sequence. + +=== JTMSK + +The letters MS are often used to abbreviate meteor scatter; the three +letters MSK mean "Minimum Shift Keying", the modulation scheme used in +JTMSK. This mode uses the same standard message structure as the slow +modes JT4, JT9, and JT65. User information is "`source encoded`" to +72 bits; a 15-bit cyclic redundancy check (CRC) is appended, and a +convolutional code with constraint length K=13 and rate r=1/2 is then +applied. This procedure makes for a total of (72+15+12)*2 = 198 +information bits for the encoded message. Three copies of the +"`Barker-11`" code and three even-parity bits are added for +synchronization, making a total of 198+33+3 = 234 channel symbols. +Modulation is carried out using a constant-envelope, continuous-phase +minimum-shift keying (MSK) waveform, with tone frequencies of 1000 +and 2000 Hz.