Digital Modes Revisited

Michael Tannenbaum K2BN

Mike-K2BN (20K) Living in Green Valley with its antenna restricted has brought back many ham radio memories. I have been licensed a long time. My original license was granted in 1952 and my lack of experience became obvious the first time I keyed a transmitter. I expected that the whole amateur fraternity would immediately recognize me the second I keyed a transmitter.

Alas even my neighbor ham 1 mile away was unable to hear me. Somehow I neglected to read the chapter on antenna tuners and I expected that if I could hear them they could hear me. I quickly learned that one needed a "resonant" antenna of some type and/or some kind of "matching" device called an antenna tuner. Unfortunately the 80 meter band (which was the only band my NC 125 heard and the only one which I had crystals for) required an antenna which was at least 135 feet long.

Unfortunately for me I lived in suburban Long Island in a house on a 100 foot by 100 foot square plot. Not enough room for an antenna. Looking at the problem from the vantage of a 17 year old, the solution was simple. Attach one side of the antenna to the side of the house and find a tree or phone pole 135 feet away, regardless if the antenna ran over the property of a neighbor. Reading the ARRL guide, I found that I could connect the antenna to my transmitter with 300 ohm TV line.

Of course the little matter of unbalanced output on my transmitter (there was a coax connecter) and the balanced twin lead did raise some concern, however I simply ignored the problem. After all I now had a resonant antenna. Unfortunately it did not work any better than my previous solution….a random wire. Going back to the book, I found that I should have continued to read the section on connecting the transmitter to the antenna. I need a coupler which required components that I did not have.

Lucky for me, I lived only 20 miles from New York City and the Cortland Street radio surplus market was in full swing. In 1952 even 7 years after the end of the war, one could find almost anything electronic at bargain prices if one knew what to look for. Everything was in black dusty boxes and was quite heavy. Also anything that could be remotely related to ham radio had become (from my point of view at 17) quite costly. After paying the train and subway fare I had only $5.00 to spend.

As I remember, the only practical solution was a BC 375 tuning unit. For those who may not know, the BC 375 and the related BC 191 were aircraft and mobile transmitters designed in the 1930s that were made in enormous quantities for use in the B 17 Flying Fortresses and army mobile ground stations. They used enormous transmitting tubes (VT-4s or 211s) and were physically quite heavy. Needless to say they were also lousy transmitters being both unstable and highly inefficient.

Most hams in 1952 had much better transmitters, but found the old anchor weights were a treasure trove of useable parts. The good news for me was that the transmitters had been designed with removable tuning units to change frequencies and I could buy just the tuning unit which contained the parts I needed to make my coupler.

Armed with my heavy tuning unit and minus the $5.00, I returned home and constructed my coupler. In the weeks that followed, I learned how to tune an antenna and load the transmitter. This knowledge has been useful to me for my entire ham career. My first contacts were dreams come true. I worked my neighbor and then stations all over the northeast but I quickly found that not everybody I called came back to me. 35 watts and a long wire just did not have enough punch to get through the crowd on the novice band.

After mulling over the problem, I thought that I had found the solution;" high" power 75 watts. In due course, I built the higher power transmitter only to find out that my neighbor’s television set picked up my new signal quite well. To solve that problem I had to relocate the antenna and add filters.

In all the years that followed, each of my ventures in ham radio encountered similar problems. My lot was too small, my income was too limited to afford updated equipment or my neighbors had too many sensitive electronic devices. In short I rarely had a radio station which could work them as well as I could hear them.

In 1975, I started to experiment with the new digital modes. I acquired a Model 15 teletype and built a simple TU using toroid filters. Aside from the noise, my relatively low powered station developed quite a reach. The Model 15 was quickly replaced by a Model 28 then a completely solid state teletype. When personal computers became generally available, I tried to attach computers to the radios with bad results. The early PCs did not have enough power to do the job. In time pressures of making a living forced me to abandon the attempt and I did not return to digital modes until I moved from Long Island to Pennsylvania in the middle 90s.

In Pennsylvania, I had a house on a hill with enough room to put up a beam and all the long wire antennas I needed. For the first time I could work any station I could hear. After a time, I began to look for more variety in my ham radio activities. In my station, I had a PC. For awhile I only used it for logging; however I acquired a "rigblaster" to hook the computer up to my radio, an ICOM 706 MK II.

The rigblaster simplified connecting the audio from the radio to the computer however it used an RS 232 line to control the PTT circuitry in the 706. An RS 232 line was required to control the frequency of the 706. The bottom line was that connecting the radio to the computer required lots of cables and lots of adjustments. I did it once but did not love the hassle.

In 2002 we moved to Arizona and my ham activities came to a halt. I was left with my mobile and no base station. The ‘706 in the car worked well until the sunspot activity dropped. Then HF QSOs became rare and I found that I did not care to be in the car for my sole ham activity. Naturally I decided to acquire a base station and began to experiment for unobtrusive antennas. My final selection of a "flagpole" antenna was a good compromise but once again I could hear them but I could not work them.

It had become obvious to me that an all in one radio such as the 706 left something to be desired. It always seemed that I was one menu away from the function I needed when I could remember what menu covered the function. Also when I wanted to monitor the local repeater and the hand held proved to be a bad choice. So I decided to get new radios. The choice for VHF/UHF a Yaesu 8900 worked well but the IC 757GX was a little too old for computer control. I now have on order a Ten Tec Jupiter which is considerably more modern.

Once the radios and the antenna were resolved, I began to investigate the digital modes again. Since I last looked at this method of operation there have been advances in both software and hardware. Several devices are available that completely bypass the computer soundcard. This eliminates a major problem in interfacing a computer with a radio. In the best case, all that is necessary is to connect the interface device to a USB port on the computer. The radio then connects to the interface device with one custom cable..

The software in the computer handles all digital tasks such as decoding the signal and printing it (if it is a text mode) or displaying it (if it is a video mode). Demonstration software was provided for the interface unit I purchased which I liked so much that I purchased a license. I must confess that the setup procedure was not painless and I am still learning, however I must have done something right because my first contact was with XE1M in Mexico City.

For those who have never used digital modes before let me briefly summarize them and explain the advantages and disadvantages of each. The oldest and most familiar digital mode is CW. CW is available on any ham band. Unfortunately it requires skill on the part of the ham to encode and decode the data. When code was required all of us learned at least 5 WPM to get a license. Sending 5 WPM is duck soup but even 5 WPM can be difficult to decode. Historically 10 WPM was a big hurdle for the novice. Above that level code started to become words instead of dots and dashes.

Now that code is no longer required for a license, many are finding that sending and receiving code is fun and requires very simple and cheap equipment. Lots of hams are using QRP equipment and single chip receivers to have a ball with this mode. There is no question that the human mind is a better decoder for CW than any computer. Experts can copy a transmission that is barely audible completely in their head. Unfortunately computers have lots of problems with hand sent code. If the sender is using a computer to generate the code and the signal is strong enough, a computer can do a fine job.

Probably the best combination for a novice is the keyboard to generate the code and the head to decode the received data. There are many ways to generate CW. The simplest is any switch which can make or break a circuit. Typically this limits code speed and can be quite fatiguing. At speeds above 15 WPM a keyer is the best choice. Almost with out exception most modern rigs include keyers. Using these keyers requires a key which has separate contacts for the dots and dashes. Typically these are not easy to handle for the novice, but skill develops over time and QSOs using keyers are typically in the 25 to 35 WPM range.

In the early days of radio, when CW was the only mode, high speed transmissions were the main method of data transmission. The data to be sent was encoded on a paper tape which was then used to key the transmitter at speeds up to 100 WPM. On the receiving end, the data drove a pen which transcribed the pulses to a paper tape. The tape was then manually decoded at some later time. Keyboard transmitted CW works in a similar manner. Data is typed in as quickly as possible by the operator and clocked out at a speed set by the computer. Typically a complete message such as a list of equipment can be selected and sent with virtually no input from the user. Under these conditions data speed can exceed 40 WPM. Common messages can also be stored such as your name and location and CQs can be sent automatically.

In the 1920s, several methods of digital transmission were developed. These methods essentially digitized the entire document and decoded it on the receiving end. The best example of this is the common FAX machine. On the ham bands FAX can be used on appropriate frequencies, however the most common equivalent is SSTV. These methods require the computer program to decode the data and display it as a picture. On the transmission side the material to be transmitted is scanned into the computer and the image is encoded for transmission. Because FAX and SSTV are limited to certain frequencies under the ARRL band plan they are hard to find. I did find SSTV on the 20 meter band at 14.230 MHz.

The most common non CW digital modes are RTTY and PSK31. Both modes require a special program to encode and decode the data. Before computers became generally available, RTTY was the most common non CW mode. A special electric typewriter called a teletype was used to generate codes which were then used to frequency shift key a transmitter (FSK). The code was transmitted at a rate of approximately 60 WPM. On the receiving side, the varying frequencies were used to drive a special polar relay and an ingenious set of levers and cams caused a typing mechanism to print text on paper. Most international and military traffic was sent by this mode until the development of the internet.

RTTY used to be quite common on ham bands and could be found on 3580-3620, 7040-7100, 14.070 to 14.095 and designated frequencies on 17,15, ,and 10 meter bands. However I noticed that it has been largely displaced by PSK31. There are many variations on the PSK model which are beyond the scope of this article, however RTTY has a very distinctive note and rhythm which can be easily distinguished from the newer mode PSK.

Fortunately you do not have to depend on your ear alone. Modern programs use a special display called a waterfall chart. All of the digital modes have a distinctive appearance on the chart. For example, a RTTY signal appears as 2 parallel lines. And a PSK signal as a single line. SSTV also has a distinctive pattern. All of the modes and their displays are described in detail in help files available from the decoding program.

The costs associated with adding digital modes to an existing HF ham station can range from almost nothing to several hundred dollars. An interface between the radio and the computer has to be obtained or constructed. Construction costs depend on the skill and knowledge of the builder. Purchase costs can range from $75 to $400 or less if obtained on an auction site such as eBay. To connect the hardware units requires knowledge of Windows XP and how communications ports and sound cards are configured.

For completely new hams HF radios suitable for use on digital frequencies can be obtained quite reasonably. All that is necessary is a transceiver capable of 100 watts power, an antenna tuner and a power supply. A good plus is a capability for the radio to be controlled by an external computer program. Radios that have those features should be available for 300 to 400 dollars. Because most activity on HF appears to be on 20 meters a simple vertical antenna will suffice.

It is odd that after 55 years as a ham, I am back to my early days with a modest antenna and a low powered transmitter…..but with digital modes, if I can hear them I can work them.