1.
UHF FF3 3-Bay Bowtie - NO Reflector (21 Oct 2015)UHF Free-Form 3-Bay (FF3) analyzed using 4nec2 after determining Dimensions using
nikiml's Python Optimization scripts.
Three alternative interconnection Topographies were determined to be of interest for
investigation (first below is the BEST). Most Bowtie Parameters were INDEPENDENTLY
varied in determining the fol. three versions of the FF3 (Free-Form 3-Bay Bowtie):
[BTW: Other Topographies were considered and found to be significantly worse.]
Note that Gain Charts are for TOTAL (Horiz. + Vert.) Gain. Azimuthal Charts show that
there is lower, but significant Vertical Gain to the SIDES of the Antenna.
a) Remove Top Bowtie from FF4 (so Offset Feedpoint) and Re-Optimize:
UHF Raw Gain = 8.6 to 11.4 dBi and SWR (300-ohms) Under 2.7 is Good.
Hi-VHF Raw Gain = 2.4 to 3.0 dBi and SWR (300-ohms) = 3.9 to 6.3 is Higher than Desired.
b) Move Feedpoint to Inner Bowtie with Crossover Feedlines to each Outer Bowtie, which
are presumably needed to ensure all three signals are In-Phase at the Feedpoint:
UHF Raw Gain = 8.1 to 10.1 dBi and SWR (300-ohms) Under 2.6 is Good.
Hi-VHF Raw Gain = 2.6 to 2.9 dBi and SWR (300-ohms) = 9.4 to 2.1 is Excessive on Ch7-11.
c) Offset Feedpoint (like a), but with Straight (NO Crossover) Feedlines to each Outer Bowtie:
UHF Raw Gain = 7.1 to 9.4 to 9.1 to 10.7 dBi and SWR (300-ohms) Under 3.1 is a Bit Higher then Desired.
Hi-VHF Raw Gain = 2.1 to 2.6 dBi and SWR (300-ohms) = 7.8 to 6.4
is Excessive. |
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