Getting started with digital modes

Jim Kajder, AF5FH
June 12, 2015

Introduction
 This presentation covers station and computer setup
for the popular HF ham radio digital modes JT65,
PSK31, and RTTY using a soundcard.

What is JT65?
 JT65A protocol was developed by Joe Taylor, K1JT in
late 2003 for EME (earth-moon-earth)
communications.
 JT65 uses 60 sec transmit/receive sequences and
structured messages.
 Exchanges the minimum information needed for a
QSO (Call Signs, Signal Reports, Grid Squares)
 Digital signal processing and redundancy allow up to
80% of the message to be lost and still be decoded
correctly.

More about JT65
 During 126 intervals of 0.372 sec the waveform is one
of 65 pre-defined tones.
 Bandwidth is 177.6 Hz.
 Accurate computer time (within 2 seconds) is
required.
 Sound of JT65:

What is PSK31?
 PSK31 was developed by Peter Martinez, G3PLX in
December 1998.
 Allows “real time” keyboard chat between two
operators. Other stations see your typing immediately.
 “PSK” Phase Shift Keying modulates the phase of a
carrier.
 The symbol rate is 31.25 baud.

More about PSK31
 Typing speed is 50 wpm.
 Bandwidth is 62.5 Hz (about the same as 25 WPM
CW).
 Uses varicode, frequently used characters are shorter
than others.
 Sound of PSK31:

What is RTTY?
 After WW II, hams began using surplus radioteletype
equipment.
 Allows “real time” keyboard chat between two
operators. Other stations see your typing immediately.
 “RTTY uses a five-bit code (Baudot) to represent all the
letters of the alphabet, the numbers, some
punctuation and some control characters.
 At typical 45 baud each bit is 1/45.45 seconds long, or
22 msec
 Typing speed is 60 WPM.

More about RTTY
 Bandwidth is 250 Hz.
 The standard mark and space tones are 2125 Hz and
2295 Hz.
 RTTY can be sent using either FSK (on/off keying,
typically from COM port or LPT port) or AFSK (audio
from a sound card).
 Sound of RTTY:

Why use Digital Modes?
 The equipment needed to connect your rig to a
computer is very modest, and can be homemade or
purchased at low cost.
 The software needed is free or low cost.
 PSK31 and JT65 modes work well with low power and
simple antennas. RTTY is a popular mode for contests.
 Many hams use digital modes on HF, and contacts can
be made anytime.

What Equipment is Needed?
 HF Transceiver capable of SSB and monitoring of ALC
(can be an older rig, or beginner rig).
 Computer running Windows, Linux, or Mac OS.
 Soundcard Interface between the computer and the
transceiver (can be homemade, and some rigs such as
Icom 7200 have built-in USB interface). RTTY is
generated using AFSK (audio frequency shift keying).
 HF antenna (simple wire antenna or vertical is fine).
 Software (free or low cost software is available).
 Optional hardware: CAT (computer aided transceiver
control)

Commercial Interfaces
 SignaLink USB
http://www.tigertronics.com/slusbmain.htm
 Rig Blaster
http://www.westmountainradio.com/rigblaster.php
 Unified Microsystems Sound Card Interface Kit
http://www.unifiedmicro.com/sci6.htm

The Computer
 For Windows a minimum 1.5 GHz dual core processor
with 3 GB memory is recommended. Same for Linux.
 An external USB sound card or second internal sound
card is recommended to avoid sending OS sounds over
the air, and to allow ham software to use computer
speakers.
 16 bit (or higher) sampling rate recommended for
sound card. WinWarbler and WSJT-X recommend
setting the sound card to 16 bit, 48000 Hz (DVD
Quality).

Software
 WinWarbler supports PSK31 and RTTY on Windows. I
use it with associated DXKeeper logging software,
which allows me to easily confirm QSO via LoTW,
eQSL, or paper/bureau. http://www.dxlabsuite.com/
 WSJT-X implements JT65 and JT9 for Windows,
Linux, and Mac OS.
http://physics.princeton.edu/pulsar/K1JT/wsjtx.html
 Meinberg NTP synchronizes the PC clock with
Internet time, which is necessary for JT65 and JT9.
Meinberg NTP Software Downloads

Software (other choices)
 Ham Radio Deluxe is the most popular software for
PSK31 on Windows. It also supports RTTY and many
less used digital modes. Version 5.24-38 is the last free
version. The current version 6.2 sells for $99.95. HRD
uses QRZ XML callsign lookup, which costs $29.95 per
year. http://www.hrdsoftwarellc.com/
 JT65-HF is the software for JT65 on Windows that I
used until development was discontinued November
2013. http://jt65-hf.com/downloads/

Software (other choices)
 Fldigi supports PSK31, RTTY, and many less used
digital modes for Windows, Linux, and Mac OS-X.
http://www.w1hkj.com/
 Several popular logging software packages support
PSK31 and/or RTTY:
 Logger32 http://www.logger32.net/index.html
 N1MM Logger http://n1mm.hamdocs.com
 Amateur Contact Log http://www.n3fjp.com/index.html

Hardware Installation
 Typically sound card interface manufacturers provide
decent install instructions:
 Tigertronic SignaLink
http://www.tigertronics.com/sl_suprt.htm
 West Mountain Radio
http://www.westmountainradio.com/content.php?pag
e=support

Additional Software
 When operating JT65, the helper application JT-Alert
http://hamapps.com/ interfaces with either WSJT-X or
JT-65HF and provides audio and visual alerts for:
 Your Callsign decoded (someone calling you).
 CQ & QRZ.
 Wanted Callsign.
 Wanted Grid (by Band).
 Wanted US State (by Band).
 Wanted DXCC (by Band).
 Wanted CQ Zone (by Band).

Software Installation
 Installation instructions are available online:
 WinWarbler (DXLab) http://www.dxlabsuite.com/
 WSJT-X has a detailed User’s Guide
http://physics.princeton.edu/pulsar/K1JT/wsjtx.html
 Meinberg NTP
http://wxtoimg.com/other/InstallNTP.pdf

Additional Help
 Besides talking with folks at your local ham radio club,
you can get help online. There are forums and groups
for DXLab (WinWarbler), WSJT-X, HRD (Ham Radio
Deluxe), JT-Alert, etc.
 http://groups.yahoo.com/group/dxlab/
 https://groups.yahoo.com/neo/groups/wsjtgroup/info
 http://forums.hrdsoftwarellc.com/
 https://au.groups.yahoo.com/neo/groups/HamApps/i
nfo

Find Your Grid Square
 Digital Mode software will ask you your grid square during
installation. Find your grid square from your call sign or
street address:
http://www.levinecentral.com/ham/grid_square.php

Tuning Up
 Too much audio output from your soundcard will
distort your signal. Typically, we set RF Power output
from the transceiver to 100%, and adjust audio output
from soundcard to achieve desired power output. ALC
should be zero. Make sure that speech compression is
off. Make sure microphone is turned off.
 With my vertical antenna, typical power output for
JT65 is from 10 to 25 watts; PSK31 is from 20 to 40
watts; RTTY from 50 to 70 watts. Your power output
will vary depending upon the efficiency of your
antenna.

Receiver Settings
 For PSK31 and JT65, set your receiver AGC (automatic
gain control) off if possible, otherwise set to slow.
 Turn the RF gain down to prevent overload of the
sound card input and/or distortion.
 I have found that NB (noise blanker), NR (noise
reduction) are best left turned off.
 Setting receiver filter to narrow, and using any notch
filter capability is very helpful when working weak
signals.

Suggested Operating Frequencies
JT65 HF PSK31 RTTY
3576 kHz 3580 kHz 3580 to 3600 kHz
7076 kHz 7035 kHz, 7070 kHz 7080 to 7100 kHz
10138 kHz 10140 kHz
14076 kHz 14070 kHz 14080 to 14100 kHz
18102 kHz 18100 kHz
21076 kHz 21070 kHz 21080 to 21100 kHz
24917 kHz 24920 kHz
28076 kHz 28120 kHz 28080 to 28100 kHz

Closing Thoughts
 When using PSK31, use lower case whenever possible.
Different characters are represented by a variable-
length combination of bits called Varicode. Lower case
letters have the shortest patterns and are the fastest to
transmit.
 Please upload your log to Logbook of the World
(LoTW) and eQSL.cc (The Electronic QSL card
center). The logging programs with DXLab and HRD
make it “one button click” to upload.
 Hope to see you on the bands!

Getting started with digital modes

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