[TowerTalk] Limited space antenna advice

Thu Sep 1 10:40:25 EDT 2005

This is a copy of a mail sent to the Elecraft list asking for advice 
regarding a new antenna setup. I thought that it was worth sending the 
message as well to this list entirely devoted to antennas and related 
topics. Unfortunately in the message to the Elecraft list I omited to 
mention that I had an e-mail exchange with antenna guru L.B.Cebik, W4RNL, 
who kindly gave me some recommendations basically to think about a 
vertical monopole with some radials instead of a vertical doublet. The 
main reason was that due to the building and neighbourhood constraints the 
lower side of the vertical doublet would be hidden between the lateral 
wall of two houses.

The scenario and past experiences are as follows:
Location: small village in the mountains (about 4000feet high) and with
strong wind storms from time to time (a wind which is called right here
"tramuntana")
Past experiences: I had to disassemble 2 consecutive vertical antennas
(CC R7000 and R7) that were about to break (no possibility to guy them).
The lower element was absolutely bent.
With both verticals I enjoyed quite a lot of DX just running 2-3 watts
(I only operate QRP)and nice chats on 40m with local stations although
in my log there are a couple of 2xQRP contacts on that band with USA
stations.
Anyway, after disassembling the R7, I started to think about a feasible
alternative to be able to operate from the weekend QTH in Pardines.
My final thoughts that I would like to share with the list members
asking for advice and recommendations are as follows.
Imagine the top view of the roof of the small house as a trapezoidal shape
.The lower side of the trapezoid measures 25,4 feet, the left side
a staight line almost perpendicular to the base about 15 feet, the right 
side (almost perpendicular as
well)about 23,3 feet and finally the top side of this trapezoid sloping
from the right to the left is about 25,6 feet.
On the top left hand corner of the trapezoid there is a tower base with
small tower element (just 5 feet high) which acts as a support for a
rugged mast where in the past were settled the verticals. The path for
the feedlines to the attic is just near the base of the tower.
I have currently 2 RG-214 feedlines about 40 feet long. One is used with
a 6m GP and the other one is free. Not too much room for other cables.
After thinking for a while about alternatives I ended with 2
complementary antennas. On one hand a fiberglass vertical marine antenna
about 26 feet able to stand the strong winds of the zone, with an
automatic antenna tuner just at the base (I recently built an LDG QRP
tuner inside a waterproof case). The main drawback would be that
according to the situation of the house I would be able to arrange some
radials only to the right of the radiator and with a maximum angle
between them of around 120 degrees. Although I am not able to simulate
the behaviour, I believe that this antenna would be useful to work with
reasonable performance on 40, 30 and 20m, but the radiation angle above
those bands would be really a compromise(??).
The complementary antenna I thought about was an horizontal
pseudo-rectangular loop with an overall length about 75 feet and about
9,8 feet above the roof. The horizontal loop would be fed on the top
left corner (near the tower) with about 50 feet of 300 Ohm slotted ribbon 
to a Z-11 tuner
in the shack. According to the literature I have been reading, it seems
that the loop would be useful on 20 and above with probably low
radiation angles on the upper bands (10,12 and 15).
When analysing how to feed the vertical marine whip I thought about 2
other possibilities or alternatives.
The first one was to throw away the remote atu and just feed the
vertical and radials with 300 Ohm ribbon. An intermediate solution would
be to feed the vertical and radials with about 13-14 feet of 300 Ohm
ribbon to the remote atu but inside the attic, just at the point where
the feed lines enter the attic.(I would arrange another 50 Ohm feedline
inside the attic). With this approach the outer RG-214 feedline would be
free for another antenna. 
One of the main constraints is that the feedlines path to the attic is
really narrow and I have still to check if the control cable for the
remote ATU will fit and travel free inside the plastic tube going from
outside to inside.(that is why I thought about the alternative of using
300 Ohm ribbon).
I hope that the scenario will be clear and would appreciate any comments
or suggestions that for sure will improve the proposed setup.
I must apologise for being so long with the description and to be using
such a huge bandwidth. I hope that my request will be helpful as well to 
others facing
similar limited space constraints, but in order to avoid too much
traffic regarding this matter on the list, I would appreciate your
comments or suggestions off the list unless the list moderator feels
that the information and feedback will be helpful to other list members.

Many thanks in advance for your patience, kind cooperation and help.

Best 72 de Vicenç, EA3ADV

P.S.- Any comments, suggestions, changes or modificactions to above setup 
will be welcome

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