On Thu, 20 Aug 1998 10:39:51 -0400 thompson@mindspring.com writes:
>
>Many have mounted a 40 or 80 rotory dipole just above another antenna.
>There have also been write-ups on using the boom either directly or
>with an extension on the low bands.
>
>I would guess that if the dipole were mounted in line with the booms
>there
>would be no problem. Mounting it broadside to the elements of the
>other
>beams is not recommended. Most of any interaction would be to the
>other
>antennas anyway except for possible boom interaction due to actual
>electrical length (elements do load the boom as capacity components).
>
>73, Dave K4JRB
>
Au Contrair !
Mounting a 40M rotary dipole parallel to the (24 ft) boom of a 3L20
or large tribander can result in CONSIDERABLE interaction for the
40M dipole. A 24 ft boom end loaded by 20M elements is self
resonant very close to 40M, therefore such a boom can act as a
parasitic element to the 40M dipole, directing most of the radiated
energy either straight up or straight down.
IMHO, it is better to place a low band rotary dipole parallel the the
elements of other antennas, spaced as far apart as possible.
Regarding 80M rotary dipoles among other antennas, it would
make sense to place the 80M dipole in the middle of a 2L40,
on or very close to the boom. This will maximize spacing to
the higher band antennas on the same mast and should
make little difference on the low bands since the elements
are such a small distance apart in terms of wavelength.
(Again, my humble opinion.... It would be interesting
to hear from Tom Shiller N6BT of F12 on this subject).
de Tom N4KG
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