UHF 3-Bay FAT Dipoles with 12 Pair of Reflector Rods (narrow Gap in the middle) analyzed using 4nec2 after determining Dimensions using nikiml's Python Optimization Scripts.
Compared to 12RR version with NO middle Gap, this version improved Raw Gain by 0.8 dB on lowest frequencies and 0.4 dB on highest frequencies. However SWR, F/B & F/R degraded. In Hi-VHF Band, the usable Forward Gain in the NO-MIDDLE-GAP version on Ch7-9 & Ch13 moved to the REAR, now being consistent with Gain on other Hi-VHF Channels. SWR is still EXCESSIVE.
HOWEVER, note that when (and if) I rerun this Optimization with a revised Target Function to hopefully adjust SWR below desired limit of 2.7, Gain advantage will no doubt shrink.
UHF Raw Gain = 11.7 to 12.9 to 12.8 dBi, F/B & F/R Min = 12.1 dB and SWR (300-ohms) under 3.1. Hi-VHF Raw Gain = 5.9 to 7.3 dBi TO REAR, F/B & F/R Min = 6.1 dB, but SWR is EXCESSIVE. Hi-VHF Raw Gain FORWARD is Very Poor.
ASSUMED DIMENSIONS (all in inches): Rdip=0.4375 = Radius of Dipole Elements (7/8-in O.D. in this model) Rfeed=0.06425 = Radius of Feedline (AWG8 in this model) DSwp=0 = Dipole Forward Sweep [If any, zero in this model] Hop=1.0 = Separation at Crossovers RR=2.0 = Reflector Rod-to-Rod Separation Rrod=0.1875 = Radius of Reflector Rods
OPTIMIZED DIMENSIONS (rounded to nearest 1/8-in): DDSep=9.0 = Dipole-To-Dipole Separation DLen=7.25 = Dipole Half-Length [Excludes Feedline Gap] FeedSep=3.25 = Separation between FEEDLINE wires ZCross=2.0 = From Center of Feedline Cross-Over to Center of OUTER Dipoles RS=4.25 = Reflector Rod Separation behind Hourglass YRod=17.0 = Reflector Rod Half-Lengths Rgap=0.25 = Gap between Reflector Rod Pairs
Date(s): 1 Sep 2014. Album by holl_ands. 1 - 21 of 21 Total. 3502 Visits.
enlarge 273KB, 1024x787 2 UHF 3-Bay FAT Dipoles + 12 Pair RR - OPT Front View There is 0.25-inch Gap in Middle of Each RR [1 large square = 2.5 inches]
enlarge 95KB, 310x1024 3 UHF 3-Bay FAT Dipoles + 12 Pair RR - OPT Top View There is 0.25-inch Gap in Middle of Each RR [1 large square = 2.5 inches]
enlarge 181KB, 1024x690 4 UHF 3-Bay FAT Dipoles + 12 Pair RR - OPT UHF Raw Gain = 11.7 to 12.9 to 12.8 dBi UHF F/B & F/R Minimum = 12.1 dB
