Topband: 33', 50', 60' inverted "L" comparison assistance request

[Terry Conboy]

At 05:47 PM 2006-11-23, k3hx at juno.com wrote:
>In preparation for the upcoming 160 meter contest, I'm trying to
>decide if it is worth the effort to increase the support height
>of the vertical portion of an inverted "L".
>
>My ground resistance is estimated to be 17 ohms and this is about as
>low as I can go given the limitations of my property.  Estimate based
>on ON4UN's book data.
>
>I'd be grateful if someone more computer-literate than I could
>determine the dB loss compared to a "ideal" full 1/4 wave vertical
>for each of the following cases.  Assume whatever toploading is
>required is acomplished by the horizontal portion of the inverted "L."
>
>Case 1:  Vertical portion 33' tall
>Case 2:  Vertical portion 50' tall
>Case 3:  Vertical portion 60' tall

Tim,
I ran these in EZNEC with #14 copper wire over Mininec ground with 17 
ohms in the ground lead.  Note that "Z" includes the 17 
ohms.  Lengths are resonant at 1.83 MHz.  1:1 SWR referenced to 
feedpoint Z.  Max gain is in the direction away from the horizontal 
wire open end.

N.B. Using Mininec ground may overestimate the gain, especially for case 1.

Up   Out       Z    Gain, dBi   Gain at 20*  F/B at 20*  BW 2:1  GndLoss
  33  101.7   25.4  -2.3 at 35*  -2.9 dBi     2.7 dB      70 kHz    4.8 dB
  50    84.7   32.0  -1.3 at 29*  -1.6 dBi     1.5 dB      90 kHz    3.3 dB
  60    74.6   36.1  -1.0 at 27*  -1.2 dBi     1.1 dB     100 kHz   2.8 dB
131.1  0      54.4  -0.4 at 23*  -0.4 dBi     0            145 kHz   1.6 dB

73, Terry N6RY