Greetings all.......
I have been wondering if someone has modeled a Robert-tail array
for 40 meters and has done a comparison to a 40-meter bobtail curtain?
A year ago, I built a Robert-tail for 40 meters. It started out as a
single 1/4 wl 40-meter vertical with 4 sloping radials. The base of the
vertical is elevated about 6' on a 4x4 post. The vertical was constructed
from the remains of an old Hygain 4BTV.
I have always wanted to try a 3-element bobtail for 40 meters. Our new
QTH is 2+ acres which would allow for some antenna experimentation. So,
after consulting ON4UN's Low Band DX book, the ARRL Antenna Handbook
regarding
bobtails, and surveying the back of our property I determined that the
bobtails would be impractical for me. The back of our property is
extremely
wooded and I would not be able to get the phasing line over the trees. So
as
an alternative and after reading the Robert-tail article in the ARRL
Antenna
Compendium Vol 2, I thought that this would be acceptable. This way I
could
use the trees as supports and also to orient the antenna in the desired
direction.
Using the existing 40-meter vertical as the starting point, I ran 2
sets
of 14-guage enamel copper wire each 65.5' in length, in opposite
directions
as the phasing lines and then the 2 end vertical elements are 31.5' also
of
14-guage enamel copper wire. The base of the vertical elements is 6'
above
ground and the elements are strung in the trees. The phasing lines are
attached to the shield side of the original vertical. The soil is
basically
sand here.
I have been extremely pleased with its performance. I have used
single verticals, 1/4 wave slopers, delta loops, and half squares for
40 meters in other locaions. Although I have no scientific data to
support
the Robert-tail, it just 'feels' better than any of the other antennas
used.
In the last 2 CQWW SSB contests I have been able to break the pile-ups
more
consistantly than anytime before.
I'd be very interested to find out how this compares to the regular
bobtail. I'll be glad to summerize the responses here for the benefit of
others.
Thanks for reading this post......
73s
Gary, KD4RH
email: kd4rh@juno.com
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