On Sun, 27 Jul 1997 12:27:17 -0800 Steve Lawrence <smlx@earthlink.net>
writes:
>Anyone have experience with the Cushcraft D4 10-15-20-40 rotary
>dipole? I
>am considering using it at around 55 feet under and parallel to a TH6
>boom.
>What 2:1 bandwidth can I expect on 40m? 73, Steve WB6RSE
>
The boom of a TH6 is end loaded by the parasitic elements with
a self resonant frequency very close to 40 meters. This will cause
it to act as a parasitic element to the D4 dipole if you place it
parallel
to the TH6 boom. The best solution is to Omega match the TH6 boom
as a rotary dipole on 40M. I have done this and it works like a champ.
The exact tuning capacitances need to be determined in place since
they will depend on the matching arm dimensions / placement and
height of the TH6 above ground.
The bandwidth of the D4 is pretty narrow on 40M since it is so heavily
loaded by the 10, 15, and 20 meter traps. A single band 40M dipole
would be a better choice if you do not wish to match the TH6 boom.
In that case, mount the 40M dipole parallel to the TH6 elements
(perpendicular to the boom) to prevent parasitic effects from the TH6.
de Tom N4KG
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