COHERENT C.W. '['%MWSLET@@R. i 1W __ .. i 1-'M - I Compiled by G31RM Issue number 27 Apri 1 1994 Postage stamps As many of you know I try to use special postage stamps on overseas copies of the Newsletter. This time it is one of a series of stamps commemorating the 25th anniversary of the investiture of the Prince of Wales. All the stamps in the set are from watercolours painted by the Prince himself. PUBLICITY - BEAM One or two German members have mentioned that they have seen an article in their magazine BEAM. COHERENT boards and programs I am maintaining a list of amateurs who have the board and program. The list includes those notified to me by Bill de Cade together with direct notifications. There are now 27 on the list which will be updated as new notifications are received. Anyone who would like a copy please let me know though I intend to include new notifications in each issue of the Newsletter. COHERENT operation There appears to be a little activity as a letter from Cliff W6HDO tells me that Dave Curry WD4PLI has copied COHERENT messages from W61ZJ and N6WHP has converted his beacon to 100 msec timing. W6HDO's beacon has been heard 200 miles away. These are all, of course, using the American low power long wave frequencies used by lowfer operators. CCW beacons There are a few lowfer CCW beacons operating in the States but now Rick VE30XX tells me that he has a one watt beacon operating on 18.101 Mhz. It sends 30 seconds of timing pulses on the minute followed by "VE3RAT CCW 1 WATT FN03 ar" which takes up a further 26 seconds. Rick has had reports from Australia, most countries in South America, about 20 states in the USA and about half the provinces in Canada. No reports have so far been received from stations this side of the Atlantic. Please send any reports to Rick Francis VE3OXX, 45 Penwick Crescent, Richmond Hill, Ontario, Canada L4C 5133. COHERENT - the G31RM mode Last time I mentioned that Bill had introduced a modification to the program which allows the audio tones generated by the program to be heard in the receiver headphones. This is version 2.3. 1 have implemented this mode by using the ACC2 socket on the rear of a TS450 as suggested by Bill. The audio level out is stated by Kenwood to be 300mv/4k7Q and this appears to be a little low to drive the sigma-delta board to clipping level. R2 on the board can be reduced to provide an adequate signal. I have found the mode very good and it avoids all the noise from my rather noisy computer speaker. I fitted an additional gain control to the ACC2 output (part of a rather comprehensive audio mixing control box used by the whole of the station) so that the level can be set correctly and this, together with the TS450 gain control, makes it possible to vary the CCW output and the normal receiver output to the headphones independently. It is also possible to have the normal output at a low level in the background when there is a CCW signal present. The CCW output and the keyboard output are both at 800 hz and the result is quite pleasing. If you try using the mode you will find odd higher pitched squeaks now and again - these appear when COHERENT pulses the transceiver tuning up or down. The TS450 menu allows beeps to be turned off if so desired but I like to hear them and they do give an audible indication of how much frequency correction is being used. The TS450 only reads out in steps of 10 hz so it is unlikely that there would be -any indication of any correction taking place if the beeps are disabled TV standards Carl Knox has spoken to the National Institute of Standards and Technology and was surprized to hear that many local TV stations in the States have started using frame synchronizers to retransmit network signals. This means that the network colour burst, which is traceable to the atomic standard, is no longer a valid frequency standard, unless it is somehow possible to receive a signal some other way. Information sheets 22 Die Grundlagen des Coherent CW in German from the magazine Funkschau 6/1982 with circuits and layouts for the Petit filter (1 2 pages) 23 Iambic keyer by Carl Knox - clock gated, dot/dash memories and fully jam proof - uses only simple gates and one shift register. It also generates automatic minimum character/word spaces of 3 and 5 units (diagrams only 3 pages) Notes from members Bernhard DF1CT now has an IBM computer so perhaps he will move over from the hardware filter to COHERENT. Karsten DL1 BEY has joined us and is distributing copies of the Newsletter to friends. He also says that Harm DK36U would be interested in CCW tests via EIVIE if there is anyone else who may be interested. DL6YCG was one of those who saw the article in BEAM as well as mine in the Amateurfunk Almanach and he has now joined us putting the membership up to 50 most of whom are now more interested in COHERENT than in the hardware version of the filter. Allan W1AEL has joined us having bought the sigma-delta board. Like others he built the Petit filter years ago. Bill de Carle has sent me another list of amateurs who have the COHERENT program. They are: DF1AE DLIBT DF2KB DJ2ZV DL2AD DL2FI DL6KL EA2SN VE3GF and W6HDO. DF2KB and DJ2ZV both ordered two complete systems, the second copies intended for use by their friends DL6KL and DL2AD, so it looks as though there will be activity from these stations even if they are only working each other. Henry ZS1AAZ now has the program and hopes to be active soon. Palmtop computers I have a little more to add to the remarks I made last time regrading the PC3100 palmtop computer. I won't go into the details but will just say that the firm I bought it from turned out to be one selling secondhand goods without saying so. I know the first one they sent was secondhand because it had the name and address of a previous owner in the memory. This developed a fault and the replacement they sent me under the guarantee was in an appalling state. It was so bad that I sent it back and asked for a refund. This is the one good thing they did - they made a refund without question. I have since bought another machine from the main supplier (who is also the designer) and this has proved to be infinitely better. In particular the oscillator is more stable - I am sure that this was what was wrong with the first machine I had and its final demise was probably due to oscillator failure. More from Bill de Carle's letters It is all too easy phychologically to see `800.0 Hz" up on the display and say to oneself, "Wow, I got it tuned in right away!" - this is wishful thinking. The point is that the frequency display will ALWAYS read between 795 Hz and 805 Hz, even if you put in a signal from a calibrated signal generator and adjusted the frequency to 793.0 Hz - in this case there would be an aliasing phenomenon, leading to a readout of 803.0 Hz. But it would be the WRONG ANSWERP! Example: say the display shows 801.0 Hz, and the operator says, 'Good enough, I'll leave it.' - Well, the actual frequency might be 801.0 Hz, but it might also be 791.0 Hz, 781.0 Hz, 810.0 Hz, 820.0 Hz, etc, etc. I will try to think of a way to make a coarse measurement and blank the frequency display if the actual frequency is not in the proper range (795.0 to 805.0 Hz). Because of the aliasing inherent in the filtering system, the program aliases ANY input frequency down to the range of 800.0 Hz plus or minus five (5) Hz. If you do not get the signal property tuned in within plus or minus 5 hertz right at the start, then the automatic frequency tracking system goes berserk (set AUTOTUNE OFF if you are connected to your rig's UP/DOWN buttons) while trying to tune in a signal initially. If your rig is tuned for an audio pitch of 790 Hz instead of 800 Hz, for example, the AUTOTUNE feedback loop will be unstable, and the system will hunt in ever-increasing swings and actually take the receiver FURTHER AWAY from the correct frequency! I know it's very important to get some kind of COARSE frequency measurement in there and to either blank the freq readout or flag it as being useless whenever the frequency is not within its tracking range. But the problem is not easy... For example there could be a strong carrier at 791 Hz who is influencing the frequency (causing it to show 801.0) - or there could be a very weak CCW carrier actually on 801.0 Hz. How to discriminate? I will have to put my thinking cap on for a while. Probably we would need to run CCW I&D filters centered on the other natural frequencies (795, 785, 775, 805, 815, 825, etc) and see what the amplitude of that same-phase signal is at those other frequencies. Sounds like a lot of work. I'll try to solve it. 73 de G31RM 2 Briarwood Avenue, Bury St. Edmunds Suffolk IP33 3QF, England.