CAKE Notes for April 14 2018
Ron arrived 5 minutes late and found the following well known subject-matter experts fully engaged in the sunny patio area of The Abbey. Glen KG0T, Don K6GHA, Gary K6PDL, Peter K6UNO, John N5HPB, Ward AE6TY and Tom KW6S. We were shortly joined by Jim K9YC and Cap KE6AFE. Sitting at the end of the long table made it more difficult than usual for Ron W6WO to hear every subject being discussed.
Don mentioned a Makers Fair to be held at Cabrillo College on May 5 and items from the Ham community would be welcome, contact Don for more info. The emphasis would be to show home-brew hardware /software items but also the excitement of modern Ham Radio in action. One suggestion was a sdr radio transmitting JTxx modes with PSK reporter or WSPR net showing a map of connections. Similarly we could demo Ham satellite and Balloon activity. Ron may be out of town on May 5th but offers assistance ahead of the event. Don reminds us that Field Day is soon approaching.
Once more John demonstrated his varied talents for designing and building just about anything. Today he showed a very neat QRP end-fed antenna tuner and in particular we admired his torroids. John is a mine of information about sources including Metric components and PCB fabrication. Decades agoTom KW6S established his reputation for R&D of many items Today it was a neat antenna selection switch. Tom has an Antenna farm in a small back yard which results in complex interaction between antennas and their feed lines. One indication of this issue was a copper shield included in his selection switch.
The topic of shielding often comes up and is currently of interest to Ron where a second N2PK VNA is under construction. Here the challenge is to have noise levels on the 5 and 12 VDC power sources so low as to not degrade the 100 dB+ dynamic range of the VNA. As we all know switching power supplies are noisy and require shielding from electric and possibly magnetic fields. The question we discussed was the choice of material to be used as a shield. Copper is commonly used because electrically induced currents are constrained by virtue of the skin-effect. Magnetic fields are only constrained by magnetic materials such as steel. Ron suggests a shield using tin plated steel could possibly benefit from the conductivity of tin and the magnetic permeability of steel. Can anyone propose an
appropriate test to quantify shield effectiveness?
The topic of noise was introduced by Jim in an entirely different context. It was asserted that applicability of the maximum power transfer theorem between a radio and an antenna was dubious. This resulted in a spirited discussion which amounted to debating whether a) Max power transfer is generally irrelevant b) Relevant only in the transmit path and c) Relevant in both directions. Thanks to Jim for this stimulating topic and welcome further discussion on this important subject at a future CAKE session. Warren’s NR0V assessment would be appreciated.
Cap showed us a list of our complete membership and a separate list of those who have not paid their dues. Frankly the high % of the latter is disappointing.
To all readers, please come and join us, or send in a question to Ron at any level of complexity All with be treated with respect at a future CAKE session.
73 Ron W6WO