SORRY. MADE A FEW MISTAKES ON THE FIRST MESSAGE. NOW, THIS ONE IS CORRECT.
73S
Talking about these things. Yesterday, I was setting up my new top-loaded
quarter wave vertical for 80 meters (see me at qrz.com). It´s made by EA5JK
and the loading system is pretty similar to those used at GAP verticals. I
got a huge metallic roof (galvanized steel, about 2000 sq/ft. not so far
from the shack) so in company with a fellow hams we installed the vertical
up in the roof and attached directly to it. Using a MFJ analyzer we found
out that the antenna tunned correctly buy we got a very low resistance
(about
20 ohmns) so we assumed that the performance wasn´t as expected. Tried a
couple of quarter wave radials that didn´t have any effect on the antenna
(not on SWR neither on impedance...strange, isn´t it?). We decided to take
the antenna down and mounted at ground level. Installed the 2 quarter wave
radials (on of them elevated) and we got the perfect 1.1 with a reactance
close to 35 ohmns and an efficiency of 99% (acording to the antenna
analyzer). After this, we connected the coax to the radio to make a side by
side comparision against my half wave dipole for 80 at 33 ft. The
propagation wasn´t quite good so I didn´t have any reply from outside of
Europe. Comparision?...well the dipole beated the vertical in about 2 S
units every time. In those cases when the signal got over 9, I had a 59+10
on the vertical and 59+20 on the dipole. The only advantage I have seen is
that the vertical is less noisy than the dipole. OTOH I´m still trying to
figure out how the hell the vertical doesn´t work out over the metallic
roof. It could be that we got so much ground plane?....Wondering if
isulating the antenna from the metallic roof and adding a bunch or radials
would let it work out. It would be a perfect location far from the
neighbour´s view...Any suggestions?. 73s all
EC1CT Fernando
E-mail: ec1ct@ure.es
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