Hi-VHF 8-Element Twin-Boom Log Periodic Dipole Array (TB-LPDA) with NO Shorting Stub analyzed using 4nec2 after finding best TAU-SIGMA Parameters and Dimensions using nikiml's Python Optimization Scripts.
Hi-VHF Raw Gain = 8.7 to 8.5 to 8.8 to 8.7 dBi, F/B & F/R MIN = 26.5 dB and SWR (75-ohms) Under 2.2.
Surprisingly COMPACT: BOOMLENGTH = 46-inches, Max Width = 34-inches. 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.
An equivalent 4nec2 Model with a Shorting Stub was ALSO run, but it resulted in a VERY LONG STUB and made NO DIFFERENCE in Performance, so Results are NOT Presented here.
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): 2 Feb 2018. Album by holl_ands. 1 - 16 of 16 Total. 728 Visits.
enlarge 73KB, 1024x718 1 Hi-VHF 8-El TB-LPDA (NO Shorting Stub) 3D View
enlarge 253KB, 1024x790 2 Hi-VHF 8-El TB-LPDA (NO Shorting Stub) Top View (46-in L x 34-in W) [1 large square = 5-inches]
enlarge 139KB, 1152x461 3 Hi-VHF 8-El TB-LPDA (NO Shorting Stub) Front View [1 large square = 5-inches]
enlarge 205KB, 1152x662 4 Hi-VHF 8-El TB-LPDA (NO Shorting Stub) Hi-VHF Raw Gain = 8.7 to 8.5 to 8.8 to 8.7 dBi Hi-VHF F/B & F/R MIN = 26.5 dB
enlarge 229KB, 1152x662 5 Hi-VHF 8-El TB-LPDA (NO Shorting Stub) Hi-VHF SWR (75-ohms) Under 2.2
