On Thu, 10 Jan 2002 "Sain'T Tom" <k4rv@mindspring.com> writes:
>
SNIP
> My experience was not unlike the W6 who experimented with high
> and low quads back in the 60s or 70s. If I recall correctly, his lower
> never exceeded the upper in signal strength.
>
> Tom K4RV
I recall that article also. To me, his observations are highly suspect.
ANY antenna higher than 3/4 WL will exhibit a NULL in the vertical
pattern and ANY antenna around half that height will fill in that null.
It's as simple as that.
These nulls can be quite deep. If you have a tall tower, the simple
solution is to place another antenna at 35 to 40 ft to fill in the nulls
of the higher antenna. Even a dipole at 35 to 40 ft will be better
than the biggest Yagi you can support at the waveangle corresponding
to the null region of the Yagi.
On 20M, a NULL occurs at 30 degrees (+/- 5 degrees wide)
for antennas at 70 ft. (600 mile skip distance on 20M) This
null is centered at 24 degrees for antennas at 90 ft. (800 mile
skip distance on 20M) *assuming flat terrain*.
My 80 ft high TH6 is typically 20 dB down at 800 miles from
my 40 ft high TH7 on 20M. That's equivalent to reducing your
power from 1000 W to 10 W. I hear W1's just fine on the
higher antenna but if I am calling someone at that takeoff
angle, and someone else is calling with a lower antenna,
the guy with the LOW antenna will most likely get through
first. Same for EU during mid day or Africa anytime, at
least from my location.
Terrain also needs to be taken into consideration if it is not flat
for several wavelengths from the tower and this may explain
some of the unaccounted for differences in observations.
Tom N4KG
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