For those who would like to explore an exciting "new" digital
mode, and if you have a PC with a 16 bit SoundBlaster compatible
sound card and a method of connecting it to your radio, you're
in for a treat! Requiring no external boxes such as TNC or modem,
but simple cabling, and working with free software, yep, FREE!,
it's an inexpensive way to get on the digital modes.
PSK31 is a new mode. Only a few years old. It is a narrow band
mode meaning that the bandwidth of each signal is on the order
of 31 Hz wide. Since it is so narrow, several simultaneous signals
can occupy a fairly small bandwidth. As an example, a normal SSB
signal occupies approximately 2.4 kHz of band spectrum. That's
ONE SSB signal! That same
2.4 kHz of bandwidth can easily accommodate in access of a dozen
or so simultaneous PSK31 signals. Two or more PSK31 QSOs can be
held, all within a few Hz of each other, and cause each other
no interference. Signal quality conditions being considered, of
The mode is very "conversational". In other words, you can expect
leisurely QSOs very much like you experience on phone or CW. Lengthy
rag-chews are common. Apparently this is a lot like RTTY but having
no experience with that mode, I can only go by what I hear. PSK31
is real time, keyboard to keyboard. The receiving station sees
what you type; mistakes and all. That's OK. That's why it's so
Getting set up is fairly simple. You take audio from your receiver
and feed it into the sound card. This received signal is decoded
by the PSK31 program and displayed as text on your computer screen.
As you type text on your keyboard, the program working with the
sound card translates that data into sound which is fed from the
sound card into the audio input of your transmitter. Most modern
radios have an accessory socket on the rear panel which provides
such in and out feeds. You will also prefer to have a way of keying
the transmitter from the computer. Typically that is done by keying
the transmit line with one of the computer COMM ports. Some operators
have used a VOX scheme with apparently good success. Most have
stuck with the COMM port method of keying the transmitter.
Low power is the order for this mode. First off, the duty cycle
recommendation for most transmitters in the 100 watt class is
perhaps 50% for higher duty cycle modes. PSK31 is a high duty
cycle mode. Unlike SSB or CW, the signal is on the whole time
that the transmitter is in the transmit mode. Most stations run
about 30 to 50 watts on this mode. Many run much lower power.
I run a whopping TWO watts of output power on PSK31! Secondly,
high power is not needed to make good contacts. PSK31 can provide
very good communication under rather weak signal conditions. Quite
often you can see clean text printout from the transmitting station
when you can barely, if at all, "hear" his signal (which by the
way has something of a warbling sound) above the noise. Apparently
the weak signal performance is superior to RTTY and perhaps the
other digital modes as well. Since it a Phase mode (thus the name
Phase Shift Keying), it is vulnerable to polar and weather related
flutter and distortion. It is possible under such conditions to
receive very strong signals from the other station, but not be
able to read the text. Oh well... Can't have everything.
It is very important that the signal be as clean as possible.
This is a very narrow bandwidth mode and distortion and widening
of the signal can occur if the audio input level is too high.
Compressors MUST be turned off and ALC action kept LOW! Overdriving
can result in not only a broad signal, but also the generation
of sidebands a significant distance from the center frequency
of the transmitting signal. This makes for undesirable interference
to other stations on the band.
Here is a screen shot of a PSK31 decoder program. Each vertical
trace in the waterfall at the bottom of the screen (by the way
the waterfall scrolls downward thus the source of the name) represents
on PSK31 signal. These are all within the bandpass of the receiver
which in this case is about 2,800 kHz wide. This bandwidth is
wide enough to contain one SSB signal. Obviously within that same
bandwidth quite a few PSK31 signals can exist. So perhaps a fifty
or more individual stations transmitting PSK31 signals can occupy
the same bandwidth as one SSB transmission. I will go into more
details on this digital mode signal decoder later in another article
here on the web site.
But... there is a great deal of interest in this mode right now.
Right now it seems like the bulk of activity is on 20 meters around
14.070 MHz. Their should be activity on the other bands as well,
and undoubtedly will be as the popularity of this mode continues
To find more about this mode and to download the free software,
visit this site: http://aintel.bi.ehu.es/psk31.html
and download the software. There are various flavors available
for different hardware and operating systems. There was also a
very good article on the topic in the May 1999 issue of QST. It
is worth the reading! An additional article in the May 2000 issue
of QST brought us up to date on new developments and revealing
new software packages now available. The new software is truly
amazing. Hardly a week passes except a new product or software
package appears on the market. Most of them are still free and
they just get better all the time.
There is also a useful E-mail Reflector you can join which will
supply to you the latest information, along with operating tips
and other useful advice. To join the PSK31 Reflector, send an
e-mail message to firstname.lastname@example.org
and in the message body simply type: subscribe
psk31. That's it.
I have drafted my Icom IC-706 into PSK31 service along with my
Butternut HF9V vertical. I've had a goodly number of very enjoyable
QSOs on this mode.
For a variation of a mode which can work with the same hardware,
check out Hell.
Nope, not the underworld location. This is short for Hellschreiber
and is a very old digital mode often referred to as a "Fuzzy Mode"
(go to the site for an explanation), but is now being brought
to popularity due to free software which can be downloaded and
run on a PC with a soundcard just like PSK31. This mode is also
a good weak signal performer, and is not subject to phase distortion
as is PSK31. As of yet it is not as wide spread in popularity,
but I'll bet it gets there. Activity is good around 14.061 MHz.
Then if someone says to you "See you in Hell", it may take on
a whole new (and clean) meaning.
Update 2003: Since this was first written perhaps a couple
of years ago, there have been significant advances in both software
available for the modes discussed here, operating practices, information
sources, and even common frequencies used. I for one have upgraded
the radio from the Icom 706 to a Kenwood TS2000 and it works great
on the digital modes. I plan to update this page with additional
information as time allows. So for now, please excuse the "oldness"
of what is written here.
Setting the Receiver Right
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