|
KL7JR'S Confined Space Stealthy Loop
6-20M
I can't say "I love
loops" enough.
It seems the more I use them the more amazed I am!
Hint. Look at the "jungle" on
right side of picture above the rails.
Now that's stealth! One section
of the loop is also barely visible on the left side.
There is also an
80 meter Tak-tenna. Can you see the antenna farm at first
glance?
The simplicity of installation and cost to
build are hard to beat. Benefits are
multi-band capability, omni-directional coverage (if that's your fancy) and gain
from some loops.
This is antenna project is another take
off of my tried and proven vertical loop design used indoors and outdoors,
but this time to fit a small space and be as "unseen" as possible from our
island oasis condominium in the Dominican Republic.
(reference http://www.hamuniverse.com/kl7jrindoorloop4010.html).
Our patio space, shown in the photo
above, now is about 16 ft long x 8 feet wide with a ceiling height of 15
feet in our newly purchased condo, occupies the top floor (3rd) of an ocean facing building.
Not many
options for antennas, and using Hamstick type antennas was my last resort.
I wanted a full wave vertical loop for 20m but the coils then had to be
very long which exceeded the 30% rule (ie-do not make the coils longer
than 30% of the wire antenna length).
Yes, I tried stretching
it to 50% and it did not work out as I was merely talking to myself most
of the time!
An easy fix for me was cutting out some wire (oh, I used
white colored wire for the entire antenna to match the patio paint!) on
the coils to arrive at 3/4 wavelength and re-stretching the antenna.
I now have a square, or almost square loop measuring 13'
horizontal x 12' vertical and a 2 foot long coil #14 wire (wound on 1"
scrap PVC pipe) in each of the vertical radiators.
Using the formula,
1005 divided by frequency we arrive at 53 feet for a 3/4 wavelength
antenna set for 14.250 MHz (1005 div. by 14.250=70.5 feet times .75=53
feet). 13' x2 plus 12'x2=50', and allow 3 feet for the 2 coils (I used 2
feet/coil). I used an air choke (6-8 wraps coax on 6 inch dia.) at the
feed point to eliminate stray RFI especially out of the neighbor's TV
set!
It is shown in the photo below.
Corner Feed Point and Choke "out of sight, out of
mind".
My fishing hole is also shown.
After a year of operating with the loop, someone from below
finally noticed
"something" and asked what the ropes were for. My flower
trellis I quickly replied!
A trip to the plant shop for some fake flower vines were in order as shown in the photo
above. I'm in good shape again until someone asks where
to get flowering plants year-around, hi hi!
I am working DX all over the world again (10-20m, and
hopefully 6m soon!) from this QTH now 1 floor higher than before. The top
of the loop is right at 40 feet above ground and the ocean fishing
hole is only 120 feet away helping out!
Come on experiment. You'll be surprised
with what a little wire will do (don't be afraid to reduce the loop if you
have to)!
73, Yukon John HI3/KL7JR
|
