At 08:50 AM 5/22/03 -0400, Paul Christensen, Esq. wrote:
>Question: Is 5/8-wave used as a compromise spread in that the difference
>between 1 w.l. and 5/8 w.l. is relatively small but closer than 5/8 w.l.
>produces quickly diminishing forward gain? Or, is there a benefit of 5/8
>w.l. that minimizes an unwanted lobe?
Here's a table of gain, take-off angle and F/B versus stacking distance for
6-element OWA 20M yagis, as computed by NEC-2. In all cases, I used the
1X/2X rule -- a classic choice for cancellation of the second forward
lobe. So If Ht = 40 feet, then the stack is at 40/80 feet, and so
on. It's fairly intriguing that the best combination of F/R and gain
happens at 90/180. Presumably this setup is not much used because the
take-off angle is too low for Europe (at least from the East Coast). I
haven't looked at how these characteristics vary across the band at the
various spacings, but I wouldn't be surprised if the "sharpness" of the max
gain and max SWR points within the band varied considerably.
Freq Ht R X SWR Gain TOA F/R
14.200 40 26.82 1.64 1.867 16.34 14 20.74
14.200 45 26.75 2.04 1.873 16.73 12 20.01
14.200 50 27.71 2.40 1.810 16.99 11 18.76
14.200 55 28.84 0.91 1.735 17.25 10 16.32
14.200 60 28.02 -0.54 1.785 17.53 9 17.10
14.200 65 26.98 -0.87 1.854 17.72 9 18.37
14.200 70 26.28 -0.73 1.903 17.81 8 19.33
14.200 75 25.86 -0.44 1.934 17.81 8 19.45
14.200 80 25.65 -0.12 1.949 17.82 7 17.76
14.200 85 25.66 0.18 1.949 17.83 7 18.99
14.200 90 25.76 0.22 1.941 17.81 6 20.74
73, Pete N4ZR
The World HF Contest Station Database was updated 9 May 03.
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