Another thought. I'm a little short of space between the vertical part of my L
and the tower which supports the far end of the loading wire. So I feature it;
the feedpoint is capacitive and below 50 ohm. I shunt the feedpoint with an
inductor which together with the capacitance forms a step-up L-network. Results
in a good match and a built in static bleed, at the expense of a bit of
bandwidth reduction.
Wes N7WS
On 12/19/2021 8:59 AM, Pete Smith N4ZR wrote:
I may be suffering from a case of too much information, but I'm puzzled by my
new 160-meter inverted L, about 60 feet vertical with 8 on the ground radials
each about 65 feet long
My old inverted L broke, so I put up a new one recently. To my surprise, it
resonated well above the band, indicating it was about 12 feet short. Because
of uncertainty about the availability of additional height at the top corner,
I temporarily added the additional length at the bottom and loosely coiled it.
Measuring the SWR and R/X at the base of the antenna with my Rig Experts AA-55
Zoom, I now see a nice textbook SWR curve centering on 1820 KHz. Measuring the
R and X at the same place, I see R of about 30 ohms and X crossing zero near
the same frequency. That seems a little low for only 8 radials on the ground
but...
So now I come into the house. The feedline is about 75 feet of RG-8X to my
tower-mounted antenna switch, and then about 170 feet of Buryflex to the
shack. I'm well aware (in general arm-waving terms) of the impedance
transformation effect of feedlines, and even at 160 this one is fairly long, but:
In the shack, I see the same nice SWR curve, centered about 10 KHz lower. The
confusion arises with the R and X curves - the R at resonance is a little
lower - about 26 ohms - but rises on the upside to about 140 ohms at the high
end (around 1920 KHz and then drops steeply to around 12 ohms by 2150 KHz.
The X value, on the other hand, crosses zero at around 1780 KHz, and rises to
around 70 ohms at 1870 KHz and then dips sharply, crossing zero again at 1915
KHz.
So, two questions:
1. Is what I am seeing simply the result of the feedline transformation of R
and X, and
2. If it proves impossible to raise the knee of the inverted L further, can I
just leave that small coil of wire in place at the bottom of the inverted L?
It seems to work pretty well - I worked a number of Europeans last night in
the Stew, although it was tough to hear them (I have not yet reinstalled my
K9AY loop).
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