On 4/27/2015 12:12 AM, Dan Maguire via TowerTalk wrote:
Jim Brown wrote:
After studying the chapters in N6BT's book that described this technique, I
spent time trying to model it, with only limited success. As I recall, I could
get good coupling (both match and radiation efficiency) with two bands (one
directly driven, one parasitically coupled), I didn't get a third band working.
It seems intuitively obvious that while the technique is elegant and the
performance of Tom's antennas prove that it works, the design is NOT trivial.
A detailed analysis of coupled-resonator dipoles may be found as the second
bullet on this page:
http://ac6la.com/aecollection4.html
I would think, meaning I don't know, but it seems logical that a fan
dipole constructed using a multi conductor cable or even close spaced
wires would have considerable capacitive coupling between elements.
With the conductors in one cable would the capacitance do more coupling
than the disconnected conductor acting as a parasitic element?
The more they are separated the more the unconnected conductor would
become parasitically driven?
I hope I got that right.
73
Roger (K8RI)
Compared to a fan dipole (elements physically connected at a common feedpoint)
the advantages of a coupled-resonator dipole are 1) independent fine-tuning of
each element, little interaction between elements, and 2) with optimal spacing
it is possible to get an *exact* match to 50 ohms on the higher (parasitic)
frequencies. (The match on the primary frequency will depend mostly on height
above ground.)
The disadvantages are 1) narrower bandwidth than stand-alone dipoles and 2) the
mechanical complexity. You need to come up with a way to maintain a uniform
and relatively small separation between the elements. That's easy to do with
tubing, not so easy with wires.
Dan, AC6LA
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73
Roger (K8RI)
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