oheirent CW Another Digital Mode! by Peter Lumb, G31RM 2 Briarwood Ave, Bury St. Edmunds, Suffolk, England Let me introduce myself and this new column. I was bom in 1922 and in 1932 passed the examination to go to my local Grammar School. One day I was looking through the books in the school library and came across one entitled 'Wireless For Beginners.' I borrowed it and read it from cover to cover. There were articles on building wireless receivers and I remember that one was a simple crystal set built from a cigar box, cardboard and wire. In addition a small piece of rock was required which had to be bought by mail from one of the big London stores. This rock arrived wrapped in cotton wool and in a beautiful little metal box together with a tiny coil of wire-4he cats whisker. The set worked well and I was able to listen to both the local and national stations. I then decided that I no longer had any interest in model railways and stamp collecting, that wireless would be my hobby. The last chapter in the book was about radio amateurs, people who were able to communicate with other amateurs around the world. This was magic. Unfortunately I was too young to apply for what was then known as an experimental license. And, by the time I was approaching the required age, World War 11 was upon us and all experimental licens- es were withdrawn for the duration of the conflict. In 1940 1 joined the Royal Air Force and trained as a meteorologist spending most of the war in the deserts of the Middle East. Believe me, weather forecasting in that part of the world is one of the easiest jobs there is apart, that is, from the occasional unpredictable sand storm. It proved to be very dif- ferent when I returned to the United Kingdom. During my time in the forces I learned enough radio theory to exempt me from the amateur examination when the war ended. It was no longer necessary to invent a reason for wanting an experimental license. It had been decided that the new amateur radio licenses would be available to all who passed a technical examination and a Morse test at 12 WPM. I passed the Morse test to become G31RM in 1952 and have held this call sign ever since. In 1977 1 noticed a couple of articles in CQ Magazine describing what was claimed to be a revolutionary new method of sending and receiv- ing Morse code. It was called Coherent CW (CCW) and was developed by Ray Petit W7GHM. Very high frequency stability was needed in all oscillators and precise timing was required. The basic element was fixed at 100 msecs for the length of a dot, giving a speed of about 12 WPM. This has been used as the standard ever since. I will not go in to the theory of CCW as it is-hoped that this will form the subject of the next column in another two months. I must, however, mention the practical side of building equipment for CCW. The original design required a very stable oscillator as the basis for all timing operations, and it was suggested that this oscillator should be stable to within Hz in 1 0 Mhz. This was difficult to achieve in 1977. As both stations in contact operated with such precise timing it was pos- sible to determine, at the receiving end, exactly when a dot or dash should appear. This was done by sending a string of dots for about half a minute, giving the receiving operator time to adjust a phasing control in his CCW filter. Once the dots were synchronized, all following dots, dashes and spaces were automatically synchronized--provided that adequately stabilized oscillators were employed. The timing had to be accurate and the transmitter and receiver oscillators had to be very sta- ble as well. In addition to the need for stability, it was also necessary to build the Petit hardware filter which consisted of a large number of digital devices. The bandwidth of the filter was only about 1OHz, which was achieved by the use of sample and dump circuits. The response of the filter was such that there were nulls every 10 hz on each side of the main response so that, provided every station used frequencies which were multiples of 1 0 hz, all stations apart from the one required fell in or other of the nulls. And, in theory at least, would not be heard. This short explanation gives you some idea of the problems involved in putting a CCW station on the air nearly 20 years ago. Apart from building the fil- ter, it was also necessary to stabilize the transmitter and receiver since no commercial equipment was available at a reasonable price. As a result the early experimenters used low power, which proved how effec- tive CCW could be. I built the filter and stabilized my rig and received nothing-there were simply no stations active. I did at one time think I heard a string of sync pulses but that could have been almost anything. Somewhat disillu- sioned I put the whole lot away in a box, in the hope that someday someone would decide to have another try at making CCW work. It was not until about eight years ago that a letter written by Bert Arnold G3RHI appeared in one of our magazines. Bert wondered if anyone was inter- ested in reviving the CCW system described many years before by Ray Petit. He received one reply, and you can guess who it was from! Me. Out came my box of bits for a rebuild, and Bert started building as well. We decided we would try for as much publicity as we could get, and wrote letters to magazine around the world. We wrote articles for mag- azines and, in the end, we collected a list of about 80 amateurs who were interested in giving CCW a try. It turned out that many of these had already tried in 1977 and some of them had built the equipment need- ed. Why, I wondered, did I not hear of them in 1977? It was then I start- ed to write a two page newsletter and sent it out to those on my list. It was free but contributions to the cost were always gratefully accepted. Several stations got on the air and a few contacts were made. I actual- ly worked four countries. Since then, progress has been very slow. However, a couple of years ago, I decided that computers were becoming very popular with ama- teurs and they were being used for CW and PITTY. Why shouldn't they be used for CCW, if someone would write a suitable program? I launched the idea in the newsletter and, to my delight and amazement, within a couple of weeks I received a computer disk from Bell de Cade VE30BE (now VE21Q) with a program called COHERENT It appeared Bill had written the program some time before for his own amusement. In the meantime he had written an article for CIST describing an audio spectral analyzer which used a small interface called a sigma-delta cir- cuit, one that would convert the incoming audio into digital pulses to pass the computer. Adding this interface to the CCW program was the answer. The program has nad many revisions since and is now available from Bill or it may be downloaded from his BBS. Apart from the sigma-delta board and the program, all you need to operate CCW is a reasonable stable transceiver and an IBM compatible computer. Here are the prices for Bill's products: circuit board only $24; full kit of parts including the board $65; all the above fully assembled and tested $95; COHERENT program disk (state size) $20. Postage is $5 and all is shipped airmail anywhere in the world postpaid. The spectral analyzer disk can also be obtained for $20, if you are interested. His address: Bill de Cade VE21Q, 29 Sommet Vert, St-Adolphe d'Howard, Qc JOT 2130, Canada. With Bill's agreement a new program called PCW should be released in the near future. This is written by Ernst Schroder DJ7HS and closely resembles COHERENT. What all is said and done it serves the same purpose so it would be expected to be very similar. It is a bit more user- friendly and has been written with the operator in mind, whereas the original program tends more towards the experimenter. COHERENT is becoming popular with LOWFER operators as it now includes BPSK, which is not included in PCW. On the other hand, PCW includes more than one bandwidth and a Morse decode to the screen whereas the output from COHERENT is via the computer loudspeaker. PCW is not available at the time of writing this but we hope to include it on the ADRS BBS in due course. Arrangements for the distribution of the pro- gram other than in the states will be announced later. It is expected to be shareware so copying will be allowed. I hope I have interested you in CCW and that you will give it a try. All we need is lots of activity on the HF bands to show how much better CCW is that CW. Let me have comments and news. As always columns of this sort cannot be run without feedback from the readers. Please note that both CCW programs will operate only when used with the VE21Q interface. There is very little activity on the HF bands at the moment, but keep a lookout 20 KHZ from the bottom of each band with 14020 being the most likely. 73, de Peter G31RM March 1995 Page 22 The Source of Digital News & Knowledge Since 1953 Digital Journal