[NLRS] New WSJT Mode for Weak Signal DX

[Lloyd - N9LB]

From: https://physics.princeton.edu/pulsar/k1jt/Q65_Quick_Start.pdf


Quick-Start Guide to Q65

 

By: Steve Franke, K9AN, Nico Palermo, IV3NWV;  Bill Somerville, G4WJS; and
Joe Taylor, K1JT 

 

December 10, 2020

 

WSJT-X 2.4.0 will introduce Q65, a digital protocol designed for minimal
two-way QSOs 

over especially difficult propagation paths.  On paths with Doppler spread
more than 

a few Hz, the weak- signal performance of Q65 is the best among all WSJT-X
modes.  

 

Q65 is particularly effective for tropospheric scatter, ionospheric scatter,
and EME on 

VHF and higher bands, as well as other types of fast-fading signals.

 

Q65 uses 65-tone frequency-shift keying and builds on the demonstrated
weak-signal 

strengths of QRA64, a mode introduced to WSJT-X in 2016.  Q65 differs from
QRA64 

in the following important ways:

 

. A new low-rate Q-ary Repeat Accumulate code for forward error correction

 

. User messages and sequencing identical to those in FT4, FT8, FST4, and
MSK144

 

. A unique tone for time and frequency synchronization.  As with JT65, this
"sync tone" 

is readily visible on the waterfall spectral display.  Unlike JT65,
synchronization and decoding 

are effective even when meteor pings or other short signal enhancements are
present.

 

. Optional sub modes with T/R sequence lengths 15, 30, 60, 120, and 300 s.

 

. A new, highly reliable list-decoding technique for messages that contain
previously copied 

message fragments.