Part F:

AL7X goes Digital

Updated 9/27/2013


For many years I have had an abiding interest in Digital communications. I could only read and dream of making it happen ...

One of the reasons I got the Icom IC-7410 is that it has all the circuitry and interfaces needed to get on HF digitally. The entire interface is a simple, USB printer cable. All the hardware is in the ICOM, and the software in the PC. No external boxes, gizmoes or maze of wires!

In my case, I wanted to try PSK-31. This is a slow speed, keyboard to keyboard system. Needs no servers or intermediaries. You tune around, find someone and give him a call.

The screenshot above shows the software that I am using right now:

  • Computer runs Linux Mint 14, an Ubuntu derivative.
  • The Program running on the computer is "fldigi".
  • For the unfortunates running windows: fldigi also runs on Windows and MAC.
  • Speed is 45 WPM. I can type faster, so I stay ahead of the buffer.
  • On the screenshot, you can see part of my contact with W6WW.
  • Red Text is me, and the black text is him.
  • On the upper left, my frequency dial is set to 14,070 kHz
  • A bit to the right you see 14,071.890, which is 1.89 kHz into the waterfall.
  • At the bottom is the waterfall display. The red streaks are stations.
  • The red vertical bars on the waterfall is where I am tuned to.
  • Other red dots are other stations, one per vertical column.
  • I count 5 stations, 4 plus the one I am working, bracketed in red bars.

PSK-31 is very economical of radio spectrum, in the waterfall width you can easily fit 20 or more contacts, yet is only 3kHz wide; ie, from 14,070 to 14,073. This not even 1% of the 20 meter band.

Contact me if you want to know more.

Very useful: The Signal Browser

Here is an incredibly useful feature that I discovered today in fldigi:

The ability to browse and track, in real time, verious QSO's in progress.

Look at the left hand side of the picture in my screenshot above. You will see, along the left column, the frequency of each particular QSO. The information on each line scrolls from right to left. This way you can see who is talking to who, who is calling CQ, etc. If you click on one of these contacts, it becomes highlighted, and in the main fldigi screen, to the right, you will see that particular signal get bracketed. You are now ready to call that person.

First Class, boys.

You do not need high power!

To make digital PSK-31 contacts you do not need high power. In fact, the vast majority of stations heard are 50 watts or less. This seems to be a gentleman's agreement among PSK-31 stations. Many are running 25 watts, 10 watts, even as low as 5 watts.

Before you get too excited, I will point out that most of those low powered stations are using good antennas. I have not heard *any* Europeans, South Americans, or Asian stations using something so poor as a vertical. They just don't make it here.

Also, before you get even more excited, you should know that most of those signals are relatively weak, and would not yield a copiable signal if they were to use that power/antenna on SSB voice. Cranking my filters down to the narrowest makes just about any PSK-31 station copiable, whereas the filter would be too narrow for voice work. Just saying ...

Part A: The Tower
Part B: Temporary 20m Dipole
Part C: The Hex Beam
Part D: Aiming the HF Antenna
Part E: The ICOM IC-7410 Radio
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Copyright 2013, Ramon Gandia