Soundcard Digital
Communications
Scott Honaker
N7WLO
Connecting Your Radio
Radio connections should be made in the
following order





Power Supply
Antenna
Computer
Mike
Key – if you must
A computer connected to the radio is the
second only to the antenna in importance
Scott Honaker - N7WLO
2
Evolution of Acronyms
Human transmitted digital

CW – Operator determines performance
Machine sent digital

RTTY – Baudot 5-bit code
Machine sent corrected data packets

Packet – APRS – TCP/IP
High noise immunity RTTY replacements

PSK31 – QPSK – MFSK – MT63
Intermittent channel weak-signal modes

HSCW – FSK441 (WSJT)
Extreme weak signal mode

JT44 (WSJT)
Scott Honaker - N7WLO
3
Soundcard Packet
AGW Packet Engine for 1200 or 9600
Supports Terminal, TCP/IP, DX Cluster,
Digipeater
APRS Software support via APRSPoint, UI
View and WinAPRS
Supports multiple simultaneous
connections
Allows remote use over a network/Internet
Scott Honaker - N7WLO
4
PSK 31
Designed by Peter G3PLX
Based on the RTTY mode of operation useful for live
keyboard to keyboard QSO
Works at 31.25 bauds
Uses varicode character coding providing 50wpm
Give very good copy under low Eb/No numbers and is
thus suitable for QRP
That instead of using FSK or on/off keying uses BPSK or
QPSK with a Viterbi decoder
Uses advanced DSP and narrow band (31 Hz!!)
techniques
Scott Honaker - N7WLO
5
PSK 31 Frequencies
HF Band
160 M
80 M
40 M
30 M
20 M
17M
15M
12M
Frequency
1807 KHz
3580 KHz
7070 KHz
10140 KHz
14070 KHz
18100 KHz
21080 KHz
28120 KHz
Scott Honaker - N7WLO
VHF Band
6M
2M
1.25
70 cm
33 cm
Frequency
50.290 MHz
144.144 MHz
222.070 MHz
432.200 MHz
909.000 MHz
Most PSK 31 is USB
6
QPSK
Quadernary Phase-Shift Keying








Four phases instead of 2 for PSK
Extra capacity used for error-correction
Improvements of up to 5 fold in error-rate
Not as good for QRP (3dB hit)
Extra transmission delay
More frequency sensitive (within 4Hz)
Must use correct sideband
Start BPSK and switch to QPSK
Scott Honaker - N7WLO
7
MFSK 16
Sixteen tone carriers, ~16Hz apart
42 WPM in 316Hz with FEC
High rejection of pulse and broadband
noise due to narrow bandwidth per tone
Low baud rate for sensitivity and multipath rejection - data bit rate higher than
symbol baud rate
Tolerance of ionospheric effects such as
doppler, fading and multi-path
Scott Honaker - N7WLO
8
MT 63
Uses 64 tone carriers
100 WPM at ~1KHz wide
Even more FEC than MSFK
Up to 25% of data can be destroyed
Long delay due to heavy error-correction
ID is generally done in CW
Scott Honaker - N7WLO
9
HamScope Software
Scott Honaker - N7WLO
10
High Speed CW
Used for Meteor-Scatter
Machine sent 100-2000 WPM
Allows contacts over paths lasting only
seconds – “pings”
No error correction
Transmission schedule negotiated
No random QSOs
Scott Honaker - N7WLO
11
FSK 441 - WSJT
Like HSCW, one uses a high-speed loop to
complete a QSO over several short bursts of
signal
100% duty cycle, so no extra energy wasted by
On/Off keying
More user-friendly interface--like RTTY or
PSK31 modes
Much better S/N than HSCW at same speed
Each character takes about 2.3ms to send with
four tones. That’s 441 baud.
Scott Honaker - N7WLO
12
FSK 441 Spectral Display
Scott Honaker - N7WLO
13
JT 44 - WSJT
Uses long term signal averaging to recover a signal that
is up to 30dB below the noise floor!
Humans have “short ears” limited by their sensory
memory—they can only analyze a signal in a small
timeframe
Computers can analyze in relatively large timeframes
Inspired by the PUA43 mode (with dedicated hardware)
Uses 44 tones, one for each character in the PUA43
alphabet (same as FSK441), plus a synchronization
tone. Each character is assigned a unique frequency
Slow transmission speed: 5.38 baud
Highly redundant (FEC)
Scott Honaker - N7WLO
14
JT 44 Signal Decoding
Scott Honaker - N7WLO
15
JT44 – Terrestrial Use
JT44 works well on troposcatter paths that
are too short for MS enhancement
Several operators have used it on 6m for
borderline TE, and marginal Es openings.
Microwave non-line-of-sight paths
Could be a good way of overcoming
atmospheric absorption above 10GHz
Contest stations can make otherwise
impossible contacts
Scott Honaker - N7WLO
16
JT44 – EME Use
JT44’s ability to recover extremely weak
signals makes it ideal for EME
Most activity by arranged schedule.
144MHz is the most popular band.
Also operation on 50 MHz, 432MHz, and
1296 MHz so far….
A pair of single-yagi stations should be
able to work each other, with QRO power
Portable EME operation can be a reality
Scott Honaker - N7WLO
17
What Does It Take?
Windows PC


Windows 98 or higher recommended
Pentium 150MHz or better
SoundBlaster compatible soundcard


Most laptop sound systems work
More expensive cards have less noise and
are more frequency stable/accurate
Interface cabling

RigBlaster or Rascal interfaces not necessary
Scott Honaker - N7WLO
18
Computer/Radio Interfacing
Line or Speaker Output
Line or Mike Input
Interface
COM Port
COM
Port
Push-to-talk
(PTT)
Receive
Audio
Transmit
Audio
144.390
Computer
Control
CI-V or CAT
Scott Honaker - N7WLO
19
Soundcard Interfacing
Most radios have audio in/out PTT on
back via a Data or AUX port
These line level in/outs are best
Mike/speaker levels can be used with
appropriate attenuation
PTT support generally via transistor or
optoisolator switch
PTT can be done with CAT port but
requires radio-specific software
Scott Honaker - N7WLO
20
PTT Switching
Scott Honaker - N7WLO
21
Soundcard Interface
Scott Honaker - N7WLO
22
Field Day Use on VHF
VHF/UHF QSO counts are notoriously low
The vast majority of QSO are voice
FD scoring gives 1 point for voice, 2 points for
CW and 2 points for data QSOs
Typical VHF QSOs might be 80 – all voice
If 50% added soundcard modes, we get 5 points
per station rather than 1
80 points becomes 240 points
This doesn’t count QSOs now possible with PSK
Scott Honaker - N7WLO
23
Remote Control
Radio tuning, antenna rotation,
transmission and reception are all
computer controllable
This software is easily remote controlled
via Terminal Server or NetMeeting
Access can be via LAN or Internet
There are shared radios on the Internet
Scott Honaker - N7WLO
24
Resources
AGW Packet Engine

http://www.raag.org/sv2agw/inst.htm
PSK 31 Home page

http://aintel.bi.ehu.es/psk31.html
WSJT Home Page

http://pulsar.princeton.edu/~joe/k1jt/
HamScope Software

http://www.qsl.net/hamscope/
MixW Software

http://www.tav.kiev.ua/~nick/mixw/mixw.htm
Rascal Interface

http://www.packetradio.com/rascalmkv.htm
Scott Honaker - N7WLO
25