codes and modes for weak-signal...
TRANSCRIPT
Codes and Modes for
Weak-Signal Communication
Joe Taylor K1JT
VHF Super Conference
April 16, 2016
WSJT-X
Codes ? Modes ??
• “Code” – symbols to represent information
– Character-by-character: Morse (CW), baudot,
ASCII, FSK441, JTMS, …
– Block messages: Reed-Solomon, Convolutional,
Turbo, LDPC codes
• “Mode” – signaling method and protocol:
coding, modulation, symbol rate, block size, …
– SSB, CW, FSK441, JT65, JT4, JT9, JTMSK, …
(also: propagation mode)
“JT” Weak-Signal Software
• WSJT – VHF-and-up: meteor scatter,
ionoscatter, aircraft scatter, EME, …
• MAP65 – Wideband EME with adaptive
polarization
• WSPR – Quasi-beacon QRP mode for
propagation testing
• WSJT-X – All bands, all modes
Many VHF-related features
> 4000 users, world-wide
Target VHF+ Propagation Types
• Meteor scatter
• Ionospheric scatter
• Aircraft scatter
• Extreme tropospheric scatter
• EME (VHF, UHF, microwave …)
• Multi-hop (weak) sporadic-E ?
} fast
slow }
Modes in WSJT-X
Scatter “Fast”
• ISCAT
• JT9 E-H
• JTMSK
• TBD ???
EME, QRP “Slow”
• JT65
• JT4
• JT9
• WSPR
Echo
Mode design: Tunable parameters
• Information throughput rate
• Block message structure
• Source encoding (compression)
• Error control coding
• Modulation type
• Symbol rate bandwidth
• Synchronization method
Optimize parameters for each purpose!
Structured messages for minimal QSO
JT4, JT9, JT65, JTMSK
CQ K1ABC FN42
K1ABC W9XYZ EN37
W9XYZ K1ABC -22
K1ABC W9XYZ R-19
W9XYZ K1ABC RRR
K1ABC W9XYZ 73
Every message is 72 information bits
Some Tuned Parameters
Mode Block
Code
Modulation Symbol
Rate
Sync
Fraction
Message
Length
JT65 63,12 (× 6) 65-FSK 2.692 0.50 46.8
JT4 206,72 4-FSK 4.375 0.50 47.1
JT9 206,72 9-FSK 1.736 0.19 49.0
JT9H fast 206,72 9-FSK 200 0.19 0.43
JTMSK 198,72 MSK 2000 0.15 0.117
JTMSK sh 24,12 MSK 2000 0.31 0.0175
TBD ??? 128,72 MSK 2000 0.15 0.075
Recent Advances in WSJT-X
• Rig control for nearly all radios
• Accurate frequency calibration
• Includes WSPR
• Franke-Taylor decoder for JT65
– Reed-Solomon, soft decision
– Open source
– Details in QEX, current issue
• Multi-pass decoding
Franke-Taylor Decoder for JT65
21 JT65 signals decoded !
2 kHz
VHF+ Features in WSJT-X
• Transverter offsets
• Automatic Doppler tracking
• JPL/NASA planetary ephemeris
Moon tracking data
• Echo mode
• Fast error-correcting mode for MS
• Auto-sequencing for fast modes
WSJT-X: Quick Tour
8 tabs
VHF stuff
Rig
Control
Frequency Settings
by Mode
& Band
Calibration
params
transverter
offsets
Automatic
Doppler
tracking
Scatter Modes
• Ionospheric scatter (6m, 4m) JT9G,H
• Meteor scatter (6m, 4m, 2m, …) JTMSK
• 500 – 1200 miles, any time!
• Aircraft scatter (10 GHz) ISCAT, JT9H
(up to ~500 miles)
50.260 MHz Ionoscatter, JT9H
Time (s)
Up to
~1300 mi,
any time!
50.280 MHz – JT9G – 15 min
N0LWF
NE: EN10
1130 mi
ND0B
ND: EN07
1327 mi
N8CGY
MI: EN74
587 mi
JTMSK, 50.280 MHz
Time (s)
VE1SKY (received at K1JT)
Testing
JTMSK
50 MHz
30 min
K1JT (received at VE1SKY)
Logging, Reporting, UDP Server
Activate
PSK Reporter
PSK Reporter - 6 m - JTMSK
144.118 MHz: K1JT at VE1SKY
(barely audible…)
Time (s)
VE1SKY K1JT FN20 JTMSK
JTMSK message duration Long: 117 ms Short: 17.5 ms
<VE1SKY K1JT> R26
<VE1SKY K1JT> 73
144 MHz
JTMSK
Short
Messages
EME modes
• 50 MHz: JT65A
• 144, 222, 432 MHz: JT65B
• 1296 MHz: JT65C
• 2.3 – 24 GHz depends on Doppler spread:
JT65C, JT9F, JT4F, …
Important hint:
EME gets “easier” as frequency increases!
10 GHz
(G3WDG)
Echo
mode
144 MHz
(K1JT)
G3WDG OK1KIR, 10 GHz
JT9E
JT9F
JT9G
H
OK1KIR G3WDG
10 GHz, JT65C
VK7MO – 10 GHz – 76 cm dish
G3WDG VK7MO
10 GHz – JT65C
G3WDG VK7MO
10 GHz – JT9F
G3WDG / P
10 GHz
EME
G3WDG / P
10 GHz
EME
WG T/R switch
Feed
50W PA
LNAs
WSJT Home Page http://physics.princeton.edu/pulsar/K1JT
Programmer details
• Open source software
• Many contributors! Particular thanks to
G4WJS, K9AN, KI7MT
• GUI in C++ and Qt
• Number-crunching in Fortran or C
• Version control with Subversion
• Anyone can build, modify as desired
See you on the air,
with WSJT-X !