I’m very pleased to receive another Guest Post from my friend Paul Coats AE5JU today!
Here is Paul recounting some of his adventures getting started in Amateur Radio:
Foreword – Steve asked me to write a few guest columns describing my trials and tribulations in ham radio for hams not very far behind me. In other words, I’m a rank beginner here. In writing my saxophone articles I quickly found that my readership was international, with many readers for whom English was a second or third language. For this reason I avoid jargon and slang. While my writing style may read as simplistic I do this so that readers will not be confused. So, with that warning, on with the show.
A year ago today I took and passed the amateur radio license tests. Before that I spent some time as a Short Wave Listener with an Icom R75. During that time I learned about a digital mode known as PSK31 and built a very simple interface to read PSK transmissions with my computer. I was soon watching conversations on the air from all over the world… Italy, Spain, Germany, Scotland, Ireland, France, and many other countries. And I found it simply incredible how little power was required for these transmissions, the signals buried down in the noise floor, to be pulled out of the muck and read on my computer screen.
One of my goals as a licensed ham was to learn how to use the PSK31 and other digital modes. This is the beginning of my journey in this direction.
PSK31 (and some other) digital signals are audio in nature, warbling tones softly whistling over the air. A look at the Wiki page for PSK31 reveals that PSK stands for Phase Shift Keying, and the 31 refers to the baud or bandwidth of 31.25 hz. This means that up to 20 PSK31 signals can be stacked side by side in about the same space as one Single Sideband phone signal. There are other versions of PSK, such as PSK63, which is twice as fast, but also twice the bandwidth.
There are many computer programs, a large percentage of which are freeware, that can encode and decode PSK31 and other digital modes. In practice this is similar to using one of the many internet chat programs where messages are typed back and forth, only without the internet.
There must be a way to get these signals from the computer to the radio to transmit, and the received signals from the radio back to the computer to be decoded and read. The connection of radio to computer is known as an “interface”. Since the signal is audio in nature the simplest way is for the audio signal to be transmitted to come out of the computer’s speakers, into the transceiver’s microphone held nearby, and out over the air. The radio signal is then received by another ham, with the digital audio signal coming out of the radio’s speaker and then into a computer microphone connected to the computer.
Just a few days ago I had a nice contact with Prof. Arnie Coro, CO2KK, host of the shortwave radio program DX’ers Unlimited on Radio Havana. You may have seen a few of Prof. Coro’s shortwave antenna plans.
Prof. Coro described his very simple interface, which consists of an electret microphone element floated in foam in one end of a short section of PVC pipe. The other end of the pipe is coupled to a small speaker. The PVC pipe prevents room noise from entering the microphone.
You would need two such devices. One would be used to send a signal from the computer to the radio, and another one from the radio back to the computer. This method not only provides audio isolation, but electrical isolation as well, to reduce the possibility of ground loops or damage to either the radio or computer.
Another way, you can simply hardwire a line from audio output from the radio to the computer, and another separate line from the audio output of the computer back to the input of the radio. Preferably these outputs and inputs will be “line level” inputs and outputs. Line level signals are fairly constant, that is, they don’t generally increase and decrease with changes of the volume knob. The signal is taken from the audio circuit before the volume control. This provides a good signal to noise ratio, a fairly strong signal well above the inherent noise floor of the audio circuitry, and reduces the number of places the audio signal must be adjusted.
It would be a simple matter to just plug audio cables from the radio to the computer’s sound card. If you have a desktop PC you will find Line In and Line Out jacks on the sound card. If you have a laptop or notebook computer, there is only microphone and earphone jacks. This is not so good for our purposes.
The first interface I used with my Icom R75 receiver was no more than a 1/8″ mono phone plug from the R75’s line out to a 1/8″ stereo plug going into an iMic USB external sound card that I use for recording with my computer. The iMic (by Griffin Technology) is different from many other USB soundcards in that it has a “line level” input and output (as well as mic level input) whereas many other USB sound cards have mic level input only.
One company, XGGCOMMS, makes cables setups for Icom and Yaesu radios. Some necessary attenuation is built into one of the connectors. These are a little better than my early attempts at reading PSK31. I have one of these cables for my Icom 718 and it works quite well, with no sign of ground loop problems.
There are other interfaces that are easy to build using audio transformers for isolation. These can be taken from old modems, telephones, and other devices.
Donner’s Digital Interfaces are ready made, yet inexpensive interfaces like the ones in the links above.
Like XGGCOMMS cable, the Donner interface requires no other cables or adapters. The device is ordered for your particular radio and everything needed is included.
And a simple Google search will find more.
In my short time using PSK31 on the air I have noticed that among hams outside of the USA most are using various such homebrew interfaces, and doing so quite successfully.
Finally, there are interfaces made especially for ham radio use, such as those by West Mountain Radio’s Rigblaster line, Tiger Electronics’ Signalink, and others. These more complex units provide more isolation, using such devices as optocouplers, and better control of signal levels. I will not try to give reviews of any of these. Reviews can be found elsewhere.
Right now, in addition to the interface cable from XGGCOMMS I have a Rigblaster Plug & Play. It is somewhat more expensive than the Donner or XGGCOMMS interfaces, but is still affordable, quite small, and very easy to use. The best thing about this is the Rigblaster Plug & Play Compatibility Chart on the West Mountain Radio website. This chart will tell you exactly which radios are compatible, and exactly what cables or adapters (if any) need to be ordered to use it with your radio. West Mountain carries all of the required cables. For example, my Icom 718 required that I have an adapter to the 13-pin socket on the back of the radio. No adapter is required for the Yaesu FT-897.
It can really be disappointing to buy a new device for the station and then find you need several difficult to find cables or adapters to get it in operation. These companies do a good job helping the buyer avoid this situation.
More next time.
I’m hoping Paul will send us more accounts of his Radio Adventures!
Note – Links corrected, as were a couple typos, on 15 Oct 09