Hi-VHF 9-Element Twin-Boom Log Periodic Dipole Array (TB-LPDA) with Shorting Stub analyzed using 4nec2 after finding best TAU-SIGMA Parameters and Dimensions using nikiml's Python Optimization Scripts.
Hi-VHF Raw Gain = 9.1 to 8.8 to 9.2 dBi, F/B & F/R Ratio MIN = 29.5 dB and SWR (75-ohms) Under 2.5.
BOOMLENGTH = 64-inches, Max Width = 34-inches with 2-in Shorting Stub at Rear, which CAN be oriented Down. Compared to 46-in 8-El LPDA, Boomlength is MUCH LONGER than expected with only 11-in due to L1/L2 Separation.
For the purposes of this 4nec2 model [which doesn't like FAT Wires], 3/8-inch O.D. Booms/Elements was assumed. However, a 1-in Square Boom and perhaps Fatter Elements is advised for rigidity. This would lower SWR by a small amount as well as increase Mid-to-High Freq Gain by a few tenths of a dB.
Note that LPDA's are 75-ohm Impedance (NOT 300-ohms) and hence require the use of a 1:1 Balun, which is typically fabricated out of some "Quarter-Wavelength" (at 198 MHz) sections of 75-ohm Coax: http://www.hamradio.me/antennas/coax-velocity-factor.html
Date(s): 4 Feb 2018. Album by holl_ands. 1 - 16 of 16 Total. 621 Visits.
