April 27th 2008
Mode to try: JT-65 A

Description
===========

JT65 is a very effective "weak signal" mode. It was originally
developed for Earth-Moon-Earth (EME) contacts on VHF.
A fairly recent development has been its use on HF where it has
proved a remarkably robust (if somewhat slow) digimode.

There are 3 submodes, A, B & C. On HF mode A is the normal choice.

One of the main differences between this mode and other digimodes
is the nature of the QSOs. It is not a simple 2 way communication
like PSK31 where you can type whatever you need to but follows a
more formalized approach to a QSO.

An example would be:

1. CQ KE7HPV
2.                  K3UK KE7HPV
3. K3UK KE7HPV OOO
4.                  RO
5. RRR
6.                  73

The "OOO" message is a shorthand notation for a minimal signal
report.

The WSJT software and now MultiPSK will calculate a SNR to be 
inserted at this point in the QSO.

A complete QSO can take several minutes and each reply/transmission
is timed to coincide with a precise time interval.


Specifications
==============

MultiPSK's help pages say this about JT65....

Baud rate:          2,69 (11025/4096) or 0.372 second by 6 bits symbol
Messages:           a message of 46.8 seconds duration begins at t=1 sec
                    after the beginning of the UTC minute and lasts until 
                    t=47.8 sec (it is necessary that the PC is synchronised
                    on a standard clock).
                    It is composed of 126 symbols, each one with a length of
                    4096 audio samples (0.372 seconde). 63 carry a synchronization
                    tone at 1270,5 Hz. 63 "6 bits symbols" carry the message
                    (allowing the Reed-Solomon coding of 72 bits).
Speed:              72 bits (or 13 characters maximum in plain text) in a 60 sec period 
                    (with only one message by period) or 2,2 wpm
Modulation:         MFSK 65 tones (64 tones for the 6 bits plus a synchronization tone)
                    with a shift between tones of 2.6917 Hz (1x baud rate) in mode A.
Receiver mode:      USB                   
Characters set:     ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+-./? 
Shape of pulse:     rectangular
Bandwidth:          178 Hz in mode A, 355 Hz in mode B, 711 Hz in mode C,
Synchronization:    automatic using the pseudo-random sequence as a reference
Coding code:        Reed Solomon (63, 12) or 63 symbols of 6 bits for 12 
                    symbols of 6 information bits (so a yield of 0.19).
Duty Cycle:         100%
Drift tolerance:    about 30 Hz/mn
Lowest S/N:         -24dB to -26dB depending on software decoding algorithm.

For complete specifications see:

ARRL's JT65 Technical Specs (PDF)
and K1JT Joe Taylor's homepage


Operating guide
===============

I would refer you to The Complete Bozo's Guide to HF JT65A
by Andy K3UK which will give you a much better idea than I can!


Recommended Frequencies
=======================

Most activity on 30m used to be at 10.139 MHz (USB dial frequency) recently however
the PropNet stations have moved down the band a little and there is an overlap between
these two systems. I would therefore recommend 10.138 MHz (USB dial frequency) as an
alternative.

JT65 has a suggested audio frequency center of 1360Hz with the sync tone being at 1270
(approx) and the upper edge is around 1450Hz. 


Availability
============

There are only 2 options for JT65 and both are free.

WSJT        http://physics.princeton.edu/pulsar/K1JT/
MultiPSK    http://f6cte.free.fr/

Spotting is encouraged and you can use the spot page at 
http://www.projectsandparts.com/30m/


Sound Sample
============

Click here to listen to a JT65-A sample (mp3 format)


73 es GL!
Sholto, KE7HPV
Republic, WA.

Comments or errata to: KE7HPV