1.
V-Stack Hi-VHF Circular Loops (16 Jul 2014)Vertically Stacked Hi-VHF Circular Loops analyzed using 4nec2.
Three Versions are presented:
a) Lossless RF Combiner Mod emulated by Two Independent Sources
b) Two Equal-Length 300-ohm (Twin-lead) Transmission Feedlines
c) Hollands Vertical Harness interconnects Stacked Antennas
[In Hi-VHF Band, all Dimensions can be rounded to nearest 1/4-inch.]
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a) Lossless RF Combiner Mod emulated by Two Independent Sources:
Hi-VHF Raw Gain = 11.2 to 11.3 dBi, F/B & F/R Ratio Min = 15.1 dB & SWR (300-ohms) under 2.9.
ACTUAL RF Combiner Loss will reduce calculated Gain by about 0.5 to 1.0+ dB.
Circular Elements = 1/4-inch Copper Tubing (QICT).
VS = 50-inches = Vertical Separation (Center-to-Center, in inches).
RS = 13.0-inches = Separation between Reflectors and Circular Loops.
[At 14.0-in, SWR is under 2.7 (preferred target) with only 0.1 to 0.2 dB decrease in Gain.]
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b) Two Equal-Length 300-ohm (Twin-lead) Transmission Feedlines:
Hi-VHF Raw Gain = 10.1 to 10.3 dBi, F/B & F/R Ratio Min = 18.4 dB & SWR under 2.3.
Rain, Snow & Ice will significantly increase Loss in the Twinlead.
Circular Elements = 1/4-inch Copper Tubing (QICT).
VF = 0.83 = "Typical" Velocity Factor of 0.83, cheap R-S Twinlead measured low as 0.77.
OPTIMIZED DIMENSIONS:
RS = 13.5-inches = Separation between Reflectors and Circular Loops
VS = 33.87-inches = Vertical Separation (Center-to-Center, in inches).
Lx = 20.87-inches = OPTIMIZED Extension to Length (in INCHES) of Transmission Line:
Lt = 26.31-inches = Lx-11.5+VS/2 = PHYSICAL Length (in INCHES) of Each Transmission Line
Le = 0.8052-meters = Lt/(39.36*VF) = ELECTRICAL Length (in METERS!!!) of Each Transmission Lines
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c) Hollands Vertical Harness (HVH) interconnects Stacked Antennas:
Hi-VHF Raw Gain = 11.5 to 10.3 dBi, F/B & F/R Min = 16.1 dB & SWR (300-ohms) under 2.3.
Circular Elements & Harness = 1/4-inch Copper Tubing (QICT).
Gap = 0.75-inches = Feedpoint Gap in Circular Loops.
VS = 50.0-inches = Vertical Separation (Center-to-Center, in inches).
OPTIMIZED DIMENSIONS:
RS = 13.75-inches = Separation between Reflectors and Circular Loops
Xh = -6.31-inches = Harness X-Axis Separation from Plane of Circular-Loops.
Yw = 2.21-inches = Y-Axis Width of Harness Separation.
Zh = 17.87-inches = Length of Harness Wires between Balun Feedpoint and Diagonal to Circular Loop.
Ld = 7.71-inches = Lengths of Diagonal Harness Wires to Gap in Circular Loops.
Lharn = 52.5-inches = 2*Zh+2*Ld+2*(0.67 for wire loop ends) = Harness Wire Total Lengths (2 required). |
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