codes and modes for weak-signal...
TRANSCRIPT
![Page 1: Codes and Modes for Weak-Signal Communicationphysics.princeton.edu/pulsar/K1JT/K1JT_VHF_SuperConference_Apr… · “JT” Weak-Signal Software •WSJT – VHF-and-up: meteor scatter,](https://reader030.vdocuments.mx/reader030/viewer/2022041104/5f0528d97e708231d4119178/html5/thumbnails/1.jpg)
Codes and Modes for
Weak-Signal Communication
Joe Taylor K1JT
VHF Super Conference
April 16, 2016
WSJT-X
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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)
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“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
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Target VHF+ Propagation Types
• Meteor scatter
• Ionospheric scatter
• Aircraft scatter
• Extreme tropospheric scatter
• EME (VHF, UHF, microwave …)
• Multi-hop (weak) sporadic-E ?
} fast
slow }
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Modes in WSJT-X
Scatter “Fast”
• ISCAT
• JT9 E-H
• JTMSK
• TBD ???
EME, QRP “Slow”
• JT65
• JT4
• JT9
• WSPR
Echo
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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!
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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
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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
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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
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Franke-Taylor Decoder for JT65
21 JT65 signals decoded !
2 kHz
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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
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WSJT-X: Quick Tour
8 tabs
VHF stuff
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Rig
Control
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Frequency Settings
by Mode
& Band
Calibration
params
transverter
offsets
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Automatic
Doppler
tracking
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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)
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50.260 MHz Ionoscatter, JT9H
Time (s)
Up to
~1300 mi,
any time!
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50.280 MHz – JT9G – 15 min
N0LWF
NE: EN10
1130 mi
ND0B
ND: EN07
1327 mi
N8CGY
MI: EN74
587 mi
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JTMSK, 50.280 MHz
Time (s)
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VE1SKY (received at K1JT)
Testing
JTMSK
50 MHz
30 min
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K1JT (received at VE1SKY)
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Logging, Reporting, UDP Server
Activate
PSK Reporter
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PSK Reporter - 6 m - JTMSK
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144.118 MHz: K1JT at VE1SKY
(barely audible…)
Time (s)
VE1SKY K1JT FN20 JTMSK
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JTMSK message duration Long: 117 ms Short: 17.5 ms
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<VE1SKY K1JT> R26
<VE1SKY K1JT> 73
144 MHz
JTMSK
Short
Messages
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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!
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10 GHz
(G3WDG)
Echo
mode
144 MHz
(K1JT)
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G3WDG OK1KIR, 10 GHz
JT9E
JT9F
JT9G
H
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OK1KIR G3WDG
10 GHz, JT65C
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VK7MO – 10 GHz – 76 cm dish
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G3WDG VK7MO
10 GHz – JT65C
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G3WDG VK7MO
10 GHz – JT9F
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G3WDG / P
10 GHz
EME
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G3WDG / P
10 GHz
EME
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WG T/R switch
Feed
50W PA
LNAs
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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
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See you on the air,
with WSJT-X !