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The MSK144 decoder cannot use such narrow bandwidths
because the signal is roughly 2.4 kHz wide. However, it can use
coherent detection. Meteor‑scatter signals generally maintain
signal coherence over the duration of a ping. Our MSK144
decoder measures a received signal frequency and phase with
enough accuracy to maintain coherence over half a dozen or
more of the protocol’s 72 millisecond frames. So, the out‑of‑
phase noise power can be rejected and we gain 3 dB over
non‑coherent detection for single‑frame decodes, and up to
7 dB for seven‑frame averages.
Summary
We hope that our description of the capabilities of WSJT-X and
its development process will inspire others to join in and
contribute to future developments in digital communication
techniques for Amateur Radio. We ourselves have many ideas
that have not yet reached fruition, but may do so in the future.
Many people have contributed to the development and success
of WSJT-X. We particularly wish to thank Greg Beam, KI7MT,
whose JTSDK software development kit has helped many
WSJT-X users build the program for themselves, from the source
code; and Dr. C.W. Suckling, G3WDG; Roger G. Sturtevant,
VE1SKY; Rex Moncur, VK7MO, and Roger B. Rehr, W3SZ, for
comments that helped us to improve an early draft of this article.
Notes
1 Joe Taylor, K1JT, Steve Franke, K9AN, and Bill Somerville,
G4WJS, “Work the World with WSJT‑X, Part 1,” QST Oct. 2017,
pp. 30‑36.
2 For more details about convolutional codes, see https://en.
wikipedia.org/wiki/Convolutional_code#History.
3 Phil Karn, KA9Q, www.ka9q.net/papers/cnc_coding.html. Joe Taylor was first licensed as KN2ITP in 1954, and has since held

4 www.physics.princeton.edu/pulsar/K1JT/wsjtx‑doc/wsjtx‑main‑ call signs K2ITP, WA1LXQ, W1HFV, VK2BJX and K1JT. He was
1.7.1‑devel.html Professor of Astronomy at the University of Massachusetts from
1969 to 1981, and since then Professor of Physics at Princeton
5 physics.princeton.edu/pulsar/k1jt University, serving there also as Dean of the Faculty for six years.
He was awarded the Nobel Prize in Physics in 1993 for discovery of
6 Joe Taylor, K1JT, “The JT65 Communications Protocol,” QEX, the first orbiting pulsar, leading to observations that established the
Sept./Oct. 2005, p. 3. existence of gravitational waves. After retirement, he has been busy
developing and enhancing digital protocols for weak-signal
7 Joe Taylor, K1JT, and Bruce Walker, W1BW, “WSPRing Around communication by Amateur Radio, including JT65 and WSPR. He
the World,” QST Nov. 2010, p. 30. chases DX from 160 metres through the microwave bands. You can
reach Joe at joe@princeton.edu.
8 Nico Palermo, IV3NWV, “Q‑ary Repeat‑Accumulate Codes for
Weak Signals Communications,” microtelecom.it/qracodes/ Steve Franke, K9AN, holds an Amateur Extra class license. He was
QRACodes‑Rev10.pdf. first licensed in 1971 and has previously held call signs WN9IIQ and
WB9IIQ. An early and abiding fascination with radio science led to
9 https://en.wikipedia.org/wiki/Costas_array his current position as Professor of Electrical and Computer
10 Philip Gladstone, N1DQ, https://pskreporter.info/pskmap. Engineering at the University of Illinois in Urbana-Champaign.
Steve is a member of ARRL and a Fellow of the IEEE. You can reach
11 Joe Taylor, K1JT, “WSJT: New Software for VHF Meteor‑ Steve at s.j.franke@icloud.com.
Scatter Communication,” QST, Dec. 2001, pp. 36‑41.
Bill Somerville, G4WJS, read Chemistry at the University of Bristol in
12 Steven J. Franke, K9AN, and Joseph H. Taylor, K1JT, the UK, graduating in 1978 with a Bachelor of Science degree. Since
“Open Source Soft‑Decision Decoder for the JT65 (63,12) graduating, he has worked in computer software and hardware in a
Reed‑Solomon Code,” QEX, May/June 2016, pp. 8‑17. variety of industries including defense, software vendors, and
financial services, more recently as a freelance consultant providing
systems programming and related services to mid- to large-size
software tool vendors. Bill has been an active Radio Amateur since
1981, holding the calls G6IJU and G4WJS. He enjoys HF and VHF
bands, contest operating, and DX chasing using CW, phone, and
data modes. He is a keen walker and swimmer. Bill participates in
open-source software projects for Amateur Radio, with WSJT-X
being the largest contribution. Bill is happy to provide input, drawing
on his extensive software engineering experience, to help those with
other important domain skills provide robust, professional standard,
software-based Amateur Radio communication tools. You can reach
For the RAC Store visit: Bill at bill.8@classdesign.com.
http://www.cafepress.ca/rac_radio
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