Good afternoon. I have 118 feet of Rohn 45G which, at the moment, has no
antennas on it. It is guyed in 3 places using Philly and sits on 1.5 cubic feet
of concrete with a pier pin at the base. The tower is grounded (three 5/8" 8
foot rods per leg, spaced at 20, 40 and 60 feet from the tower in a line and
all connected with #2 copper) and I have layed out 33 130' radials (#14
stranded copper, insulated) as the ground screen. If you disconnect the ground
rods (not the radials) the tower has a resistance of 37 ohms at 1.830 and an
SWR of 2 (according to my MFJ 259B). I would prefer, however, for lightning
protection, to leave the ground connections in place and use a gamma wire and
capac itor to match the tower for use on 160. I have tried, using a wire
running from near the top of the tower, and with spacing from the tower varying
from about 28 down to 14 or so inches, to find the 50 ohm tap point for the
tower. This seems to occur, interestingly enough, at about 3 feet off th
e ground. Since this seems a bit odd I consulted local antenna guru, N4KG, and
he too thinks the tap point should be significantly higher, at least 30-40 feet
if not more. I don't have much experience with this to draw on so I would like
to ask the group for ideas or input. This also seems to vary quite a bit from
articles I have read on the subject in the ARRL antenna book and in Low Band
DXing, although virtually all of those articles concern towers with some sort
of top loading provided by yagis. Thank you in advance for your advice, Steve,
NN4T
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