CAKE 3/12/16

CAKE Meeting March 12, 2016

It was a dreary morning and several other events competed for attendance, so my thanks go to Warren NR0V, Kerry K3RRY, Glen KG6T, Art AC6P, Peter K6UNO, Ward  AE6TY, and Fred KJ6OOV

Our guest speaker, Steve Stearns, K6OIK is a long-time Ham , distinguished scientist in the realm of EM transmission systems and a prolific author. Steve shares his knowledge freely as In this instance he presentation began with an introduction to the Smith Chart and progressed to further illustrate its power in studying the design of networks to match the output of a transmitter (aka Generator) and a load, presented by an antenna. The Smith Chart models assumed a generator with an output impedance of 50 Ohms connected  by a zero loss transmission line of 50 Ohms to the load.

 The purpose of a matching network is to reduce reflections on the transmission line at frequencies (plural) of interest. Their value can be seen on charts showing SWR vs frequency. A rectangular X-Y chart and a Smith Chart have the same information but the Smith Chart is far more helpful as it provides tools for modelling and simulation. Steve acknowledged the work of Ward Harriman AE6TY for his superb implementation called SimSmith.

Steve’s focus was on finding networks of L and C components to match at multiple frequencies. One  example showed how to cover the 80m band at two frequencies. It was clear that matching at two discrete frequencies doesn’t imply broad band.  If networks are added to increase the number of discrete frequencies bandwidth at each diminishes to practically nil.

The phrase  “conjugate match ” came up and  Steve discussed why it had caused so much consternation that the ARRL has essentially banned it from their publications.  I my not so humble opinion I think the problem is that the term has been misapplied and would benefit from sober re-assessment which is now unlikely.

Our CAKE sessions are intended to promote questioning and curiosity so I hardly ever leave fully satisfied and I hope that is true for others. For example the schematics all showed the source as 50 Ohms regardless of the behavior of the generators active devices or their associated frequency dependent components.