Thanks for the interest in my report of my experience with 160m inverted L
using tower as the vertical section.
The tower legs were set in concrete and copper strip was led from each leg
to an earth pin, maybe 6ft long galvanised steel rod as used for grounding
household electric systems in ZL,.
Rods went into clay, were intended purely as lightning protection , imagine
them pretty useless as rf grounds, and probly not too great as lightning
grounds.
cables fron beam and rotator were formed into coils at the bottom of the
tower becos I read somewhere that helped keep lightning type discharges from
running along the cables.
I ran a thickish wire, actually two lengths of medium heavy plastic coated
stranded hookup wire from a bolt at the botttom of one tower leg up to the
point up 40ft where the gamma wire joined the tower. from there it was
bonded to the tower close to the top, from there it spiralled (helixed? ) up
the 20ft spike above the beam. The spike was thin wall high strength alumin
alloy, quite thin wall, about 1.75 od. The spike fitted inside the 2in stub
mast hiolding the beam. I did not go to any great lengths to bond the spike
to the stub mast. Was experimenting. There was a light weight marine grade
plastic pulley attached to the top of the spike. there was a halyard up tio
the pulley, idea being that I could drop and modify the flat top as I
wished.
I left a bit of sag in the flat top, there was no problem with the spike
rotatiing with the beam.
the conductor up the tower was intended as an electrical bond to bypass the
section joins which were suspect rf conductors. The wire was taped to the
tower leg.
I beleive this made the tower itself the vertical radiator, but did not
measure rf in the legs.
The gamma wire went down and out to a palstic pipe spreader avbout 1m long,
from there angled out to an insulator attached to a peg on the ground, and
then angled back to a 500pf series vable cap in a box between the tower
legs. I played with the distance beween the bottom of the gamma and settings
of the cap and got SWR to 1:1 easy.
I made a solenoid balun by winding ?20 turns of coax around a 4in plastic
drain pipe. This was hard by the feedpoint. Worked well enough, a F12 balun
was a marginally better (but more expensive).
Make no great claims for this antenna, for me the nice part was how easily
it tuned up after wasting a lot of time trying to get the thing to take
power with other (all sub optimal) ground plane/earth mat arrangements.
73
Barry ZL1DD
--
Barry Kirkwood PhD ZL1DD
barrykirkwood@gmail.com
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