CAKE Oct 17, 2015
CAKE Oct 17
We were pleased to welcome Craig N6SBN for the first time and nine of our regular members attended. This was a good turnout given the conflict with Pacificon, it’s very tough to find open dates these days.
Beginning at one end of the table were discussions with Frank K6BDK on the various extreme low bandwidth digital modes designed by professor Joe Taylor K1JT. It is hard to believe that we can reliably communicate (if not converse) across the world with elementary antennas and less than 10 Watts of radiated power. These modes are now in common use for moon bounce.
Next we saw the latest Dongle collection by Tom KW6S. These tiny SDR radio models now range form HF to UHF and some include a transmitter. Please do not use them to control your neighbors door bells et al !! I have invited Tom to present Dongle capabilities and low cost at a future CAKE date tbd. Tom showed a product made by W6PQL that attends to the critical sequencing required by solid state amplifiers.
Warren NR0V is now well known for his efforts to counter noise in various forms both at the receiving and transmitting. A graph showing the performance of a suite of his filters is simply staggering and only achievable using Digital Signal Processing (DSP). As a side-bar I am including some comments on filters for those who may wish to read further. At several past CAKE sessions we have been recording the joint efforts by Glen KG0T and Kerry K3RRY to invent and build their micro-controller work-bench (for lack of a better designation). This is now complete so Congratulations Chaps !
Once more we have an excellent opportunity for a future show-and-tell session. Glen remarked about the FORTH computer language that became quite popular in the 80s and reported to be still going strong. The rather special experience at CAKE sessions is to observe really inquiring minds at work.
Eric KK6IZY and Kerry are a class duo. Their obscure topic today was the failure modes of LED flashlights. The discussion evolved to consider the degree of water proofing of different models, battery life, colour and light intensity. One of their discoveries was that some models drain the battery even when switched off. Ron W6WO dropped one on a semi-hard surface recently and was surprised that it ceased to work. Seems strange given the robust nature one might expect.
Moving round we had Don K6GHA delivering an intense introduction to contesting for Craig’s benefit. Don showed a product, BCD-14, used to provide control signals between a radio and amplifiers /tuners. This might be an application for Glen’s micro. Ron reported on the success in building a dual band 10m/30m dipole. This antenna is for experiments with the diversity feature of the ANAN radio on 10m and to try the popular 30m band for digital modes.
Some of us plan to visit the California Historical Radio Society in Alameda on the 24th Please stay tuned for our next CAKE session on Nov 7th 73 Ron W6WO Here is a brief dissertation on filters Filters are essential to all forms of communications. They serve two purposes, one is to separate wanted information from unwanted information, noise and distortion. The second is to pack as many simultaneous channels of communication as possible in a given media. A very long time ago I worked in a company that had a whole department dedicated to filter design. The job was so technically demanding that only the best and brightest in the pool of candidates needed to apply. (I never did). The reason it was such a challenging job is that filters in those days were designed by mathematics, coupled with an intimate knowledge of conductive, insulation, magnetic and dielectric materials. The performance of many such basic materials was also fast evolving. In those day filters only used discrete inductive and capacitive components and such filters are in common used today particularly in the high power stages of amplifiers and tuners. It isn’t too hard to design them today but lacking software design tools the process of evaluating designs is laborious. Active devices (initially vacuum tubes) were introduced to improve filter shape, loss and bandwidth. A hot topic of the times was a trade-off as the dynamic range of filters could be reduced by the active components. Reverting back to Warrens graph my mouth opened before my brain switched on (no comment please !) and I asked about their dynamic range. Warren gently reminded me that in the DSP world the key factor limiting filter behavior was the point of overload in the Analog-Digital convertor. Within that limit, and given the number of samples and bits/sample, was is possible to derive the superb filters that he illustrated. Thanks for leading the way Warren.
—Ron Skelton W6WO