Introduction to the HF
How to get started the "Easy" way in HF digital communications using PSK 31.
This article is NOT intended as a
technical description of how to us PSK 31 or any other digital
mode but is intended to get you interested in starting the fun
of using your computer sound card, simple interfacing to your hf
transceiver and computer keyboard for real time keyboard to
keyboard, over the air, QSO'S on the HF bands using digital modes.
You will learn the basics of what
you need to get started in this fun method of using very low power in
restricted antenna situations to communicate with fellow hams worldwide
using a simple station setup. It's really easy when you know what you need
and are not afraid of trying it.
Many hams are of the opinion that computers and ham radio do not mix! Well fellow hams, unless you live in the dark ages, I am here to say that you are not informed!
Can you imagine trying to copy a radio signal that is so weak and AT or IN THE NOISE LEVEL or BELOW that you can hardly hear it in your speaker? How is this possible?
The answer is by using your computer and special software and an interface with your transceiver. With this simple setup the computer software can filter out most of, if not all of that noise that you normally hear with your ears, and you can get at or near 100% copy of that "signal" using many of the digital mode software programs that are FREE! What the station operator types on his keyboad is what you see on your computer screen, in real time. All of this is accomplished using a software program that is usually free, a simple radio to computer interface and your transceiver! Using your transceiver in USB mode, tune around 14.070Mhz carefully and you should hear many PSK31 stations on the air. You won't be able to "copy" them without some sort of interface and the software installed on your computer!
Ok, you have convinced me, maybe...., so what do I need and how is it used?
A little background first:
One of the most popular hf digital modes is PSK31 due to the simplicity of using it. It has been around for many years and is used all of the time by many hams worldwide on a daily basis and on many of the hf bands. It's ease of use and setup with your station makes it a top choice among most hams who enjoy going "digital" on the ham bands. So exactly what is it?
(A bit of technical stuff)
The mode, PSK31, is typically created by a software program, (many are free), that either decodes the received signal in the receive mode or generates an amplitude and phase modulated waveform that is converted to an audio frequency analog signal by a sound card which in turn is fed to the transceiver during transmit.
PSK31's bandwidth of 31.25 Hz was
chosen because a normal typing speed of about 50 words per minute (if you
can type that fast), requires a bit rate of about 32 bits per second,
and specifically because 31.25 Hz could easily be derived from the
8 kHz sample rate used in many DSP systems, including those used in
the computer sound cards commonly used for PSK31 operation (31.25 Hz
is 8 kHz divided by 256, and so can be derived from 8 kHz by
halving the frequency eight times).
PSK31 was developed and named by English amateur radio operator Peter Martinez (G3PLX) and introduced to the amateur radio community in December 1998.
PSK31 was enthusiastically received by a few hams, and its usage grew like wildfire worldwide after the word got out and it's popularity grew by leaps and bounds over the air waves. Due to the efficiency of PSK31, it became, and still remains, highly popular with ham radio operators whose circumstances do not permit the large antenna systems and/or the use of high power due to many location restrictions. In fact, high power is NOT needed with PSK31! Typically only 20 to 30 watts is all that is needed.
A PSK31 operator typically uses a single sideband transceiver connected to the sound card of a PC running PSK31 software. When the operator types in a message for transmission, the software produces an audio tone which sounds, to the human ear, like a continuous whistle with a slight warble. This is then fed through either a microphone jack (using an intermediate resistor to reduce the sound card's output power to microphone levels) or an auxiliary connection interface into the transceiver, where it is transmitted. Most operators use a commercially built interface between the transceiver and the computer designed specifically to do all of this which saves on lots of building time.
From the perspective of the transmitter, a PSK signal amounts to little more than somebody whistling into the microphone at varing rates and tones. However, the software rapidly shifts the phase of the audio signal between two states (hence the name "phase-shift keying"), forming the character codes. These phase shifts serve the same function as the two tones used in traditional RTTY and similar systems.
Resistance to interference(1)
PSK31 can often overcome
interference and poor propagation conditions in situations where voice
(ssb) or other data methods of communication fail. However, PSK31 was
only designed for leisure use by amateurs, and due to its relatively slow
speed and minimal or no error control, is not suitable for transmitting
large blocks of data or text, or critical data requiring high immunity
from errors. It's a FUN mode that is very enjoyable on the air and many
hams spend hours just "looking" rather than "talking". Even when the
higher frequency bands like 12 and 10 meters "appear" to be "dead", you
tune up on the most used PSK or digital mode frequencies...and watch the
"waterfall" display ...you may be surprised at what is "alive"
To decode PSK31, the received audio whistle (the actual tones and warbles from over the air that you may hear at times), from the transceiver's headphone output, is fed into the sound card's audio input along with all of the noise that the receiver hears), and the software decodes the PSK mode digitally. Even many of the very weak signals seen on the screen of the program display that your ears may not hear are decoded. This is what is so remarkable. You are decoding signals you may not hear well from the radio speaker! All you hear from your radio speaker is noise from it and very weak whistling sounds unless the transmitting station has a strong signal.
The PSK software also includes a user interface and control screen on the PC monitor, which is used to display the decoded text and manage the software configuration. You simply see the tracks of the signals on a "waterfall" screen and pick one with your mouse and the program does the rest. (See the screen shot below). You look in another window and see the decoded text that the other operator is sending. So basically you may usually see many signal tracks side by side on the "waterfall" display (a slowly moving background that looks like a colored waterfall) and pick from one with your mouse. The program decodes it an you see what he is sending as it is being typed at the speed of light (real time) by him and then you can reply back to him using your keyboard over the air! Your keyboard or mouse keys your transmitter and you are having a QSO in real time as you type your comments while they are being transmitted back to the other station!
The use of PSK31 does not require
exclusive use of a dedicated computer. When it is not running the PSK31
program, such as DigiPan (reported to be the
most popular PSK program due to ease of use),
the station computer can still be used for normal use as needed. Because
PSK31 was developed for use through a computer's sound card, many programs
have since been created to use the same technology for other modes, such
as RTTY, Hellschreiber, Olivia, MFSK etc. So once it has been set up to
run PSK31, a computer and interface can be used
to explore a variety of digital modes using the program or
others, and the interface, which is a MOST important part of
the setup for digital modes. Using a poorly home brewed interface
will cause you more problems than QSO'S!
DigiPan program description:
DigiPan stands for "Digital Panoramic Tuning". The program brings a panoramic display on your computer screen and allows the use of your mouse to pick and choose from the stations displayed for receiving and transmitting for the band frequency you are monitoring. Point and click and you are ready to go! DigiPan provides a panoramic display of the frequency spectrum nearby your VFO frequency in the form of an active horizontal dial scale extending the full width of the computer screen. Depending upon your transceivers IF bandwidth, it is possible to "see" and choose from many stations at one time using the panoramic display depending on band conditions.
Screen shot above (scaled down for web page) of the DigiPan panoramic viewer in action on the 20 meter band. The green Flag over the red diamond symbol shows the station selected! You willl notice the frequency coverage is from 14.069Mhz to over 14.073Mhz (receiver set to "wide") as viewed from left to right in the panoramic viewer above. Not shown is the actual text that is being received in another window in the program.
OK, I'm hooked! I want to try thisout! What do I need for the setup to get me started and on the air quickly?
Aside from a standard hf radio ssb transceiver, very little equipment or skill is required to use PSK31 or other digital modes for that matter. Good typing skill is a help but many operators use the hunt and peck method. Normally, an older PC and a few cables will suffice and many PSK31 software applications are free out there on the internet. You simply download the free programs and install them which is a simple process. Hook up the interface (see info below) between the radio and the computer sound card and get on the air.
To save loads of time, and in many cases some frustration, and some foul language, many operators now use commercially available products such as interface/modem devices between their computers and radios as they save much "getting started" time in getting set up and operating because...... you have to find the plans for the interface, understand them, acquire the parts needed, shipping, find the correct cables to interconnect it all, build it, test it and if it does not work, you have to figure out why and on and on. If you don't want to build your setup from scratch or can't for some reason then read on......
Get to the details already!
You should already have much of the
needed equipment, your computer and your hf transceiver, so you can mark
that off your list. The most important part of
getting on the air with hf digital modes like PSK31 is the radio to
The "EasyDigi" interface by KF5INZ.....makes it
I love it! Plain and simple! You can take this as my recommendation for this radio to computer interface for the digital modes or not. This is up to you but when I heard about it, I wanted to give it a try. I was introduced to the KF5INZ products at a local ham radio club meeting by a fellow ham who had built one from scratch in kit form! I was impressed with it at once and the price was very "right"!
I did a bit of research on these interfaces on the web and contacted Clifford, KF5INZ, at his company where they are made and sold wanting to get one for my Icom IC-718 so I could try it out on PSK31. (He offers it in kit form or ready to use custom built for most rigs. I chose the ready made model but you won't believe how inexpensive the kit is! This is what caught my eye at first having been introduced to it in kit form at my local ham radio club by another ham operator.
I did some quick math in my head after looking at the kit and parts, quality, etc and decided that there was no way I could come up with all of the parts needed, plus the board to mount them on, a case for it, shipping charges, etc at the price my fellow ham paid for his!
Plus....I simply just did not have the time to build one.
So....shortly after contacting Clifford and getting one on order, he emailed me wanting to know if I would do a simple test for him on my rig so he could make sure that his interface would work properly on it. The test turned out fine and he said "good to go" for the Icom IC-718 to be used with it.
A few days later I received it well
packed and I opened the shipping box and was thrilled at how small it
was and so well made. All of the "electronics" are in an enclosure
that measures only about 3 inches by 1 1/2 inches and is made of
heavy duty ABS. The enclosure even comes with mounting tabs or
"brackets" on the ends if you want to mount it out of the way!
All of the needed jacks are installed and the enclosure is fully labeled appropriate to your radio and ready to go. It came with all the needed cables and even schematics, an internal circuit board parts layout diagram, hookup diagrams, and a mic plug on a long cable all wired for my transceiver. There where urls included where I could go to get the driver for it to work with my Windows XP computer. And the best part, Made in the U.S.A. in the great state of Texas!
Getting it going and hookup:
I will be honest.....hookup and getting it to work correctly, was a problem at first...dummy me! In my haste to get it hooked up to the computer and radio and to get on the air quickly, I had reversed two cables and the power output was way down regardless of my sound card or transmitter settings! I found my "dummy" mistake, reversed the cables and all was well! This was like, "you can't see the forest for the trees", reversed! Repeat...dummy me! After I discovered my mistake and reversed the cables, it worked fine.
On the air with the KJ5INZ Interface!
PSK31 operation was simple using the KF5INZ interface and the DigiPan program worked correctly with it displaying those beautiful yellow colored streams of "paint" falling down the blue "waterfall" background. 20 meters was in fairly good shape at the time of my testing and I made several contacts back to back using only about 10 to 20 watts output fed to an old "junker" converted base station CB antenna converted loosly to 20 meters and a tuner. The interface pumped out the PSK31 signal without a problem!
I did, after a while, test it using
FLDIGI, but not being familar with that program, it did take some reading
of the Help files. The FLDIGI probram, at least to me, is a much more
complicated program with a high angle learning curve. After my self help
tutoring, the interface worked fine on it also and more good contacts were
made using it on 20 meters. I also used the KF5INZ interface with Ham
Radio Deluxe and the Airlink software...all work great with
Ease of use...after you hook it up, set your sound card settings and com port. Your ready to go!
Could I build it for the same or cheaper price?Absolutly not, unless I already had everything in my "junk boxes" including all of the cables, jacks, plugs, computer connections, enclosure, circuit board, soldering skills, etc.
These devices incorporate the necessary impedance matching and sound level adjustment to permit the sound card output to be injected into the microphone input, or the accessory jack on the rear of your rig in many cases and the radio audio output to be sent to the sound card input, and also handle the radio's transmit-receive switching via your keyboard. Recently introduced interfaces also incorporate their own sound card, and can therefore be powered and run from the PC via a single USB connection. The latter are much more expensive than the more simple interfaces like the "Easy Digi" from K5INZ and usually perform much the same function. So these expensive interfaces are usually not needed and are overkill in many cases in my opinion!
Spectrum efficiency compared to other modes
PSK31's efficiency and very narrow bandwidth make it highly suitable for low-power and crowded-band operation. PSK31 contacts can be conducted at less than 100 Hz separation so in theory, you can get about 10 stations operating within a 1KHz wide space on the band and usually using as little as 20-30 watts or LESS, so with disciplined operation at least twenty simultaneous PSK31 contacts can be carried out side-by-side in the bandwidth required for just one SSB voice contact! Do not use audio compression...turn it off! Use of it will cause splatter and poor use of bandwidth, distortion of your signal, etc.
Common PSK 31 Frequencies
The following amateur radio frequencies
chart shows the bands and frequencies that are commonly used for
transmitting and receiving PSK31 signals. There are many others also. They
normally occupy the lower edge of each band's digital modes section and
are not etched in stone. PSK31 operators generally use upper sideband
(USB) even on frequencies below
10 MHz where the convention normally
calls for lower sideband. This is because (a) signals then spread upwards
in frequency into the digimode section from the "base" frequency, and
(b) using QPSK requires both stations to use the same
frequencies listed above are typical but not fixed in stone. Tune as
needed around them.
*Current usage based on observation, is centered on 7.070.15 and 21.070.15. 7.035.15 is commonly used in Region 2 as of 2012. There is no authoritative list as the frequencies are determined by common useage and band crowding.
Summary, Footnotes and other good info.
If you have never tried the "digi" modes on HF, I encourage
you to get started very simply using PSK31, a great interface like the
ones from K5INZ, and your ssb rig. Just because you are limited by antenna
restrictions, lack of high power, or the space for outdoor antennas does
not mean that you can not make contacts on the air. Very low power and a
simple indoor antenna will get you into the exciting world of digi modes!
Give it a try! 73 de N4UJW
Download the free
DigiPan program here.
If you consider using DigiPan for PSK 31, very good help (other than the Digipan Help file that comes with the program) can be seen at the links below:
Good help info for DigiPan can be seen here!
Another good help article for DigiPan here! (pdf format)