Also had problems with adding 12m quad to a 10-15-17-20M 4 element GEM
quad. These four bands coexisted very well even with a single
feedline. Looked at it in AO and the patterns on all four bands were
reasonable. The model did show a degredation in F/B ratio relative to
a single band antenna. It didn't drop below 15db which was fine with
me. Front/side ratio was also less but still reasonable. The forward
gain seemed unaffected-- except on 10m where there was approximately
1db loss in gain. The azimuthal pattern was wider and appeared to be
smeared (two headed) due to contributions from the 20M elements.
These calculations on 10M were a bit suspect because of the limited
number of pulses allowed. The spreading of the pattern could have
been due to not having enough segments to numerically converge out a
numerical harmonic from the answer. Anyhow, direct A/B comparisons of
the 4 el quad on 10 (approx 20' boom on 10M) consistently outperforms
a 3el 12' boom antenna at the same height on another tower. That was
good enough for me.
When I tried adding just a 2 element 12M quad, things went completely
to pot on 10M. Measured impedance on 10 went wild. Attempting to
resonate the 12m quad was a failure. Reducing driven element length
significantly didn't alter the resonant point hardly at all! It
seemed clear that feeding the 10 and 12 driven elements at the same
time just was a bad idea. Was not able to model the five bands in AO
because of too few segments. Finally gave up and built a separate 2
el quad and put it on another tower with a TV rotor.
I'm not saying it can't be done. I did help a fellow put up a 2 el 5
band lightning bolt quad up. It used a single feedline and appeared
to work.
Perhaps there are some unique dimensions which make it look acceptable
from an SWR standpoint. It would be interesting to model the
lightning bolt quad to find out how the patterns look.
73 de Brian/K3KO
Maurizio Panicara wrote:
>
> Place a 12m director in front of the 10m driven and see what happens using
> your modeling software, or roughly check how the 12m director lenght
> converge to a 10m reflector using the typical formulas.
>
> 73,
> Mauri I4JMY
>
> > This 12/10M interference is a puzzling concept.
>
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