Hi-VHF 9-Element Folded Dipole Yagi, including 3 Reflector Rods, MCM Stellar Labs 30-2475, analyzed using 4nec2. Initial Dimensions were provided by user [MikeBear]. Analysis revealed that Antenna per MikeBear's Measurements were very close to OPTIMUM, for the chosen use of Three Reflector Rods....but Repurposing Two RR's as Directors improved Raw Gain on Ch13 by about 1 dB and F/R Ratio improved several dB on Lower Channels.
Several Versions are presented here [For comparison, completely Re-Optimized 9-El FD-Yagi's are Analyzed in another Album]:
a) Per MikeBear Measurements with Upper/Lower Reflector Rods 2-in in FRONT of Middle Reflector Rod:
HiVHF Raw Gain = 8.7 to 10.8 dBi, F/B & F/R Ratio = 10.3 to 21.0 to 19.2 to 19.8 dB [Poor on Low Channels] and SWR (300-ohms) is Under 2.2 (EXCELLENT).
Moving the X and/or Z-Coordinates of the two Upper/Lower Reflector Rods in vicinity of current locations did NOT significantly improve either Gain, SWR or F/R Ratio. Boom Length = 59.375-in + Ends.
==================================== b) Analyzed Upper/Lower Reflector Rods Repurposed as Two Additional Directors: [Requires a Front Boom Extension.]
THESE ARE PRELIMINARY RESULTS...NEED TO REDUCE GAIN ABOVE 216 MHz TO HOPEFULLY IMPROVE F/B: HiVHF Raw Gain = 8.6 to 12.0 dBi, F/B Ratio = 14.1 dB and SWR (300-ohms) Under 2.2.
Improves Ch13 Gain and F/R Ratio on Lower Channels. SWR is Excellent. New Boom Length = 95.7-in + Ends
c) Upper/Lower Reflector Rods were removed to investigate improvement to F/R Ratio (at expense of Raw Gain). See below Charts for results.
d) ALL three Reflector Rods were removed to investigate improvement to F/R Ratio (at expense of Raw Gain). See below Charts for results.
e) Location of Upper/Lower Reflector Rods relative to Middle Reflector was Re-Optimized, but there was NO overall improvement when Constrained to be BEHIND the Folded Dipole.
==================================== CORRECTION (14 Dec 2015): This 9-El FD Yagi Analysis replaces Earlier Analysis (8-El FD Yagi) that was MISSING Director just 2.5-in in front of Folding Dipole. There was only a few tenths of dB change in Performance....but SWR increased from 3.0 to EXCESSIVE 3.7.
Date(s): 14 Dec 2015. Album by holl_ands. 1 - 34 of 34 Total. 2127 Visits.