Hi all...I am new to this list, but I am hoping that some members might be
able to assist in an antenna problem I think I have...first off I have
recently installed a KLM 3 el 80m yagi....its at 175 ft and I spent most of
the past summer re-building the antenna and installing hardware etc...the
antenna was built exactly according to KLM spec's in the manual...lengths
were measured and are within less than 1/8 in from spec.....here in lies the
problem.....the antenna has a feed point impedance of 100 ohms...almost
every 3 el design I can find in YO, AO, YW and any other yagi design program
has antennas with 25 ohm impedances for 3 ele designs....The original KLM
design used a pair of 75 ohm Teflon coax cables 1/4 wavelength in length in
parallel to a 1:1 balun at the feed point to provide a nice match....well I
had to make a single 75 ohm 1/4 to transform the 100 ohm to a 50m ohm
match....
I plan to make another trip to the top of the tower next week to plot x and
y values from 3.2 mhz to 4.2 mhz to see if I have overlooked
something....the antenna as it is now has a W shaped resonance curve...its
1.2:1 at 3523 and goes slightly up to approx 2:1 and then dips back down to
1.1:1 at 3799 mhz...so it has a very acceptable match....
The actual performance is far less than I would expect though....there are
many times at sunset that the 4 square I have will beat this yagi into
EU....there have only been a few times that the yagi has beaten the 4 square
in EU or JA....but it sometimes does occur.....the yagi shows approx 20-25
db f/b.....
Are 80m conditions so flaky that the yagi will at times not equal the 4
square?? I am puzzled by the 100 ohm feedpoint impedance also??
Any comments either here or offline would be appreciated...thanks de Rick
nq4i
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