PSK-31 FOR THE BEGINNER
Roy McCluskey (G0AXJ)
You may already know something about PSK-31 but have never tried it.
This article outlines some of the essential things that you need to consider
before you can get yourself up and running using PSK-31 mode of
PSK-31 (Phase Shift Keying at 31 baud)
PSK-31 is a digital communication mode developed by Peter Martinez
(G3PLX). It modulates the phase of a single audio tone, transmitted
normally in USB mode (Phase shift modulation). The transmission is
constantly at 31.25 baud, with a variable length code (Varicode), where
characters used more often have shorter bit codes. As a result, the
transmission rate is about 50 words per minute.
The output power required to transmit PSK-31 is very low, typically 5 - 30
Watts only is recommended (25 watts being the norm for most operators).
Using in excess of this creates problems for other users of this mode
because transmitting PSK-31 at higher power levels causes the signal to
‘splatter’ over other amateurs' signals (You will not be popular and most
amateurs will not work another station who is causing problems).
PSK-31 is probably the most effective digital mode presently in use. Theory
has it that there can be over 90 stations in QSO at any one time within a
bandwidth required for one SSB signal (without causing QRM to other
Something that I really like about this mode is that it was essentially aimed
at keyboard to keyboard (conveying typed messages) communication and
whilst typing you can correct errors even while the text is being
Where to find PSK-31 transmissions
You will always find PSK signals on the 20 Mtr band around 14.070 MHz.
However, the following bands also see plenty of PSK activity too:
1.838 MHz (160m) 3.580 MHz (80m) 7.035 MHz (40m)
10.140 MHz (30m) 14.070 MHz (20m) 18.100 MHz (17m)
21.080 MHz (15m) 28.120 MHz (10m).
What you will need
You will need a simple interface between your transceiver and personal
computer with an appropriate software program to decode the PSK
signals. Modern technology has made the connection process much easier
today due to the fact that computers are installed with sound cards, USB
connections which are standard in all computer systems.
Digital Radio Interfaces
There are many appropriate interfaces available with differing price tags. I
use the SB-2000 Radio Interface (CG Antenna) which costs around £100.
However, you can purchase custom built interfaces which come with leads
to match your Rig for around £30 (see links on last page). Be aware that
when you purchase an interface you will also require the leads for the
particular transceiver that you wish to use (At an extra cost of around £20),
or you can wire up your own leads for a fraction of the cost.
There are many different software packages on the market that can be used
for digital modes. Some offer a selection of modes enabling the operator to
work a variety of different digital modes while others are specific to one
mode, MMTTY for example, is for use with RTTY only.
Some software is free and easily downloaded (See my links at the end of this
article). I use MixW 2.19 and costs around £45 to register (See below). The
software also contains a log-book facility which automatically indicates if
you have worked a station before. MixW allows you to have independent
windows open, each monitoring signals and capable of decoding different
digital modes at the same time.
Basic screen view of MixW 2.19 Software
Waterfall – is the area where signals are monitored. Once you have set up
your transceiver, interface etc you will see cascading shapes forming in the
waterfall area. To receive and decode signals all you need to do is place the
mouse cursor to the centre of the signal trace and left click (See the figure
Waterfall with PSK-31 cascading signals
Setting it all up
Roger Cooke (G3LDI) has produced a useful book entitled ‘RTTY/PSK31 For
Radio Amateurs’ available from the RSGB for around £8. This explains
nearly everything you need to know in order to use PSK-31.
Inter-Modulation Distortion (IMD)
Assuming that you have the necessary items connected to the Rig and
computer you will need to setup the sound card and audio levels. Make
sure that the transmitter’s speech compression is off.
Signals are measured using IMD. To ensure that signals are not over
modulated causing distortion, you need to check your audio output signal;
this is the audio signal level being fed to the transmitter. I used another
radio operator to provide my IMD reading while adjusting the audio levels
to an acceptable level (most software provides a visual IMD reading whilst
receiving signals). Ensure that the power output is around 20 watts.
The following IMD measured in – db (minus db) will give you an idea of
what you should be aiming for:
A good IMD idling received signal should be between -20 to -30db
A poor IMD idling received signal is -19db and lower
The worst signal -10db and lower should be avoided at all costs
because of the spurious signals generated
Setting up – Adjust the rig to the ALC setting
Monitor the ALC when advancing the audio so that the meter needle just
enters the ALC scale. Then turn down the audio drive so that the needle is
set just outside of the reading scale (you should be looking for a needle
deflection which does not enter the ALC scale).
It is best that you get a report from another station in order to find out
what your IMD status is. Once done you do not need to alter this again.
The diagram below shows you what a good PSK-31 signal looks like in
comparison to a poor one:
Listen before you transmit
The best way to learn a little about this mode of operation is to tune into
PSK-31signals and monitor QSO’s. You will soon learn how other operators
communicate and also what sort of information they exchange.
One really advantageous provision that the software provides you is
macros. Macros are files usually programmed by the user that are invoked
by pressing a certain keyboard, although most software packages have
standard text already compiled, these can be edited and changed for your
Software enables the user to send [TX] information quickly. If the interface
is set up correctly and configured to a COM port, pressing the transmit [TX]
button will automatically invoke PTT and send any composed text to the
station you are working.
Another really useful aspect of digital radio software is that most of the
packages that I have experimented with provide details of the Station
callsign you are working, for example:
Distance in Km and miles
Stations you may have worked before and the bands that you have
I hope you have found this article useful and I hope to see you on my
For useful information please see the links below.
Ham Radio Deluxe (HRD)-Free http://www.ham-radio-deluxe.com/
MixW 2.19 http://mixw.net/
Others are also available (See Roy G0AXJ)
SB-2000 Radio Interface from most major amateur radio suppliers in
M0AQC Interface (Your rig make/model & he provides a nice interface
for around £25) email: email@example.com
See his web: www.m0aqc.co.uk
Build your own: http://www.gm4kgk.co.uk/PSK.htm