G1HEQ's Ham Radio Site

The digital modes provide a wonderful opportunity for those of us who would like to work on the HF bands but find CW too difficult and SSB phone prohibitive because of interference problems. These modes require very little power to work the world. Generally 25 to 50 watts is plenty of power. The digital modes are comparable to CW in that their bandwidths are very narrow. Bandwidths generally range from about 30 to 200 Hz compared with SSB which is 2,100 Hz. This is a huge difference and one of the main reasons why the digital modes are so effective at low power. Because of their low power and modulation schemes, the digital modes do not interfere with telephones and answering machines in the neighborhood the way the SSB often does.

The digital modes are easy to set up and get operating. What is needed is an HF rig, a computer running one of the many software programs that are available either for free (most are) or for a small purchase price, and a hardware interface between the computer and radio. Most computers come with a sound card and these modes work via the sound card input and output circuits. A fairly easy interface between the sound card and radio can be built for around $7.00 or a very nice and very adequate interface can be purchased that will handle any chore you might throw at these modes.

Best of all, the digital modes are incredible easy to use. The major software programs utilize a waterfall display that shows all of the signals currently operating on the band. All you have to do is click on a signal with your mouse, and the QSO pops up on your computer screen. It doesn’t get any easier than that.

The digital modes described in this article are mainly found on the High Frequency bands and will require a General class license or above (except on 10 meters where a Technician with morse code privileges can operate from 28.100 to 28.300 MHz).

There is a wide choice of digital modes to choose from. However, the most popular modes today are PSK31, BAUDOT (RTTY), MFSK-16, and PACTOR. PSK31 is the most popular of the digital modes because it is very effective at low power, is easy to set up (it requires only an HF radio and a computer with a sound card), and its waterfall display makes it extremely easy to use. Baudot RTTY is the second most popular, particularly for DX and contest work. RTTY is the oldest of the digital modes. However, new software with waterfall displays and using the computer’s sound card as the HF radio interface has given the old standby a new look. MFSK-16 is one of the newest modes that shows considerable promise. It is a good weak signal performer, reportedly better than PSK31, particularly for DX contacts that involve signal paths that pass through the Earth’s polar regions. It is a little more difficult to operate than PSK31 but does use a waterfall display and sound card radio interface. PACTOR is the most popular of the error correcting class of digital modes that includes AMTOR, Clover, and G-TOR. These modes utilize relatively complex protocols that automatically detect and recover from transmission errors through a combination of forward error correction and automatic retransmissions. They are excellent for message handling in that they deliver error free text to the computer screen. However, they are more than what is needed for most casual amateur radio QSOs. Because of their complex protocols, these modes require a multi-mode hardware controller box between the computer and HF radio. The multi-mode controller makes these modes more expensive to implement and a little more difficult to operate than the modes using waterfall displays and sound card interfaces. One point to mention about the sound card interface is that once you have it installed, you can switch between the various modes that use the interface (PSK31, RTTY, MFSK-16, and others) by simply activating the appropriate software package on your computer.

Where on the HF bands do you find hams using the digital modes? The following chart shows you were to look.

BAND

PSK31

RTTY

MFSK-16

PACTOR

80 Meters

3.580 - 3.584

3.580 - 3.620

3.610

3.580 - 3.620

40 Meters

7.070 - 7.074

7.080 - 7.100

7.080

7.080 - 7.100

30 Meters

10.130 - 10.140

10.130 - 10.140

10.130 - 10.140

10.130 - 10.140

20 Meters

14.070 - 14.074

14.070 - 14.095

14.080

14.070 - 14.095

18 Meters

18.100 - 18.105

18.100 - 18.105

18.100 - 18.105

18.100 - 18.105

15 Meters

21.070 - 21.074

21.070 - 21.100

21.080

21.070 - 21.100

12 Meters

24.920 - 24.925

24.920 - 24.925

24.920 - 24.925

24.920 - 24.925

10 Meters

28.120 - 28.124

28.070 – 28.120

28.130

28.070 - 28120