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On Tue, 3 Oct 2006 13:33:21 +0100, Ian White GM3SEK
wrote: The missing part is the velocity factor of the twin-lead when acting as a stub, which means that the electrical length of the stub is different from the physical length. Which of those two lengths would you use in the NEC model? Hi Ian, This is simply a veiled expectation for EZNEC not being able to model the "special attributes" of the antenna. The answer is easy for a single-band model; but it's not so easy to create one NEC model that will be valid for all the bands this antenna is designed to cover. The answer is even easier than that. The Lattin antenna has a basic rationale behind it that does not demand two different lengths: stub tuning which is an electrical quality (not physical). What acts like a stub, acts like a stub for any wire mesh modeling a stub. The Lattin antenna does not exhibit this action to any correlation to frequencies attributed to it. It is THAT simple. Appeals to physical size relate only to the far field radiation characteristic. Even here the Lattin is noted for being un-notable. You don't need to worry about velocity factor, or dielectrics when the basic rationale calls it a stub and it doesn't work as a stub for bare wire. The Franklin antenna employs some of the same geometries and nowhere makes a desperate grab for theoretical underpinnings called stubs. Yet the Franklin delivers as promised if or when you add dielectrics. The Franklin's simple distribution of currents (which works for every antenna) works without having stray wires tacked on like Irish Pennants. There are more apologists for this design than working Lattins flying their tuning wires (in their notorious disregard for the rationale of the design). The fact of the matter is that modeling lays bear the myth. 73's Richard Clark, KB7QHC |
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