At 12:34 PM 20070907, Eddy VE3CUI  VE3XZ wrote:
>Would I benefit from (possibly) optimizing the low angle radiation
>of my inverted "L" antenna, if it was to be cut exactly
>1/4wavelength  as opposed to it being 170' long (overall), and
>tuned by way of a variable capacitor at the base...?
>
>Note: the vertical portions of each "L" here is about 70' tall...the
>horizontal 100' balance is true horizontal, away from the vertical portion.
It would probably be difficult to detect much difference in low angle
signal between your current configuration and a shorter version. The
signal for closein stations via high angle paths could drop about 6
dB with a shorter top wire due to reduced horizontally polarized energy.
My EZNEC model of your invertedL show gains at a 15 degree elevation
of +0.4 dBi forward and 1.0 dBi reverse (in the direction the open
end of the top wire points), with 1.6 dBi at the zenith. It is
tuned with 321 pF series cap (Q=1500) for resonance with a resulting
44 ohm feed impedance. SWR 2:1 bandwidth is about 66 kHz (50 ohm
reference) or 63 kHz (44 ohm reference).
With a simple 1/4 wl resonant invertedL, with a 64.3 foot top wire,
the gains are +0.1 dBi forward and 0.7 reverse, with 7.7 dBi at the
zenith. Feed impedance is about 28 ohms. SWR 2:1 bandwidth 77 kHz
(referenced to 28 ohms).
For an invertedL with 70 feet vertical and 60.8 feet horizontal,
tuned with a 4.73 uH (Q=200) shunt at the feedpoint to match 50 ohms,
the gains are +0.0 dBi forward and 0.7 dBi reverse, with 8.5 dBi at
the zenith. SWR 2:1 bandwidth 77 kHz.
"Average" ground (MININEC), a 5 ohm ground loss resistance, and #14
bare copper wire are assumed. (The top wires are only 0.13 wl high,
so using MININEC ground approximations will introduce some errors,
which I hope are similarly optimistic for all three versions.)
73, Terry N6RY
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