W8JI:
>While that system probably works, with proper selection of feedline
>lengths or use of baluns there would be no need to switch the
>shield.
If I recall correctly, the feedlines must be open-circuit (OC)
because ~3/8 wavelength OC adds inductance to make the undriven elements
look like parasitic reflectors in the system. I guess they could be
made ~5/8 wavelengths and shorted if you didn't mind the cost of another
1.25 Vf wavelengths of coax (5 X .25 wavelengths X Vf). I would still
worry about what is happening in the system if the shield is grounded
to the tower and all other shields (driven and undriven). The modeling
probably only considers the undriven dipoles as reflectors and not part
of a complex system with shields of everything tied together.
This system is completely different than the intended use of
Comtek or Stackmatch systems since it is parasitic and not driven.
73, Bill W4ZV
P.S. Personally, I would go with a driven system (Comtek) if I were
using full-size dipoles...you only need 4 instead of 5 and the results
are more predictable using a forced system IMHO.
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