The Antennacraft FM13 is a Log-Yagi array with 13 elements on a 140″ boom. Five of the elements are driven.
I modeled the antenna with the AO-Pro 8.50 Antenna Optimizer program. This image shows the antenna geometry.
This shows segmentation detail for the phasing lines and feedpoint. Blue dots mark analysis segments. The red dot is the feedpoint.
Below are calculated performance figures for a segmentation density of 50 segments per halfwave. Mismatch loss is due to SWR. Wire loss is due to conductor resistance. Mismatched gain is forward gain including wire and mismatch losses. F/R is the ratio of forward power to that of the worst backlobe in the rear half-plane. The SWR reference impedance is 300Ω.
88.000 MHz: Impedance 268 + j24 ohms
SWR 1.15
Mismatch Loss 0.02 dB
Wire Loss 0.08 dB
Mismatched Gain 8.23 dBd
F/R 20.05 dB
93.000 MHz: Impedance 200 - j36 ohms
SWR 1.54
Mismatch Loss 0.20 dB
Wire Loss 0.06 dB
Mismatched Gain 8.62 dBd
F/R 21.93 dB
98.000 MHz: Impedance 252 + j20 ohms
SWR 1.21
Mismatch Loss 0.04 dB
Wire Loss 0.04 dB
Mismatched Gain 9.02 dBd
F/R 23.53 dB
103.000 MHz: Impedance 132 - j133 ohms
SWR 2.80
Mismatch Loss 1.10 dB
Wire Loss 0.16 dB
Mismatched Gain 7.95 dBd
F/R 15.03 dB
108.000 MHz: Impedance 174 + j3 ohms
SWR 1.72
Mismatch Loss 0.32 dB
Wire Loss 0.19 dB
Mismatched Gain 8.22 dBd
F/R 13.08 dB
Antennacraft FM13
Free Space
98.000 MHz
77 6063-T832 wires, inches
de1 = 15.75 ; driven element locations
de2 = 25.75
de3 = 35.75
de4 = 45.75
de5 = 55.75
d = .11 ; phasing-line diameter
r = 3 / 2 ; half of rivet spacing (insulated elements)
h = 10 / 2 ; half of DE spacing
y1 = r * (1 - 2.375 / h) ; y at first phasing-line bend
y2 = r * (1 - 2.875 / h) ; y at second bend
y3 = -y2 ; y at third bend
y4 = -y1 ; y at fourth bend
x1 = de1 + 2.375 ; x at first phasing-line bend, rear line
x2 = de1 + 2.875 ; x at second bend
x3 = de2 - 2.875 ; x at third bend
x4 = de2 - 2.375 ; x at fourth bend
x5 = de2 + 2.375 ; x at first phasing-line bend, second line
x6 = de2 + 2.875 ; x at second bend
x7 = de3 - 2.875 ; x at third bend
x8 = de3 - 2.375 ; x at fourth bend
x9 = de3 + 2.375 ; x at first phasing-line bend, third line
x10 = de3 + 2.875 ; x at second bend
x11 = de4 - 2.875 ; x at third bend
x12 = de4 - 2.375 ; x at fourth bend
x13 = de4 + 2.375 ; x at first phasing-line bend, forward line
x14 = de4 + 2.875 ; x at second bend
x15 = de5 - 2.875 ; x at third bend
x16 = de5 - 2.375 ; x at fourth bend
s = .375 / 2 ; half of phasing-line crossover spacing
1 0.0000 -34.0000 0.0000 0.0000 -2.0000 0.0000 0.3750
1 0.0000 -2.0000 0.0000 0.0000 2.0000 0.0000 1.1
1 0.0000 2.0000 0.0000 0.0000 34.0000 0.0000 0.3750
1 15.7500 -30.3750 0.0000 15.7500 -r 0.0000 0.3750
1 15.7500 r 0.0000 15.7500 30.3750 0.0000 0.3750
1 25.7500 -28.5000 0.0000 25.7500 -r 0.0000 0.3750
1 25.7500 r 0.0000 25.7500 28.5000 0.0000 0.3750
1 35.7500 -26.4375 0.0000 35.7500 -r 0.0000 0.3750
1 35.7500 r 0.0000 35.7500 26.4375 0.0000 0.3750
1 45.7500 -25.4375 0.0000 45.7500 -r 0.0000 0.3750
1 45.7500 r 0.0000 45.7500 25.4375 0.0000 0.3750
1 55.7500 -21.8750 0.0000 55.7500 -r 0.0000 0.3750
1 55.7500 r 0.0000 55.7500 21.8750 0.0000 0.3750
1 63.7500 -24.0625 0.0000 63.7500 -2.0000 0.0000 0.3750
1 63.7500 -2.0000 0.0000 63.7500 2.0000 0.0000 1.1
1 63.7500 2.0000 0.0000 63.7500 24.0625 0.0000 0.3750
1 77.3750 -24.0625 0.0000 77.3750 -2.0000 0.0000 0.3750
1 77.3750 -2.0000 0.0000 77.3750 2.0000 0.0000 1.1
1 77.3750 2.0000 0.0000 77.3750 24.0625 0.0000 0.3750
1 89.3750 -24.0625 0.0000 89.3750 -2.0000 0.0000 0.3750
1 89.3750 -2.0000 0.0000 89.3750 2.0000 0.0000 1.1
1 89.3750 2.0000 0.0000 89.3750 24.0625 0.0000 0.3750
1 101.3750 -24.0625 0.0000 101.3750 -2.0000 0.0000 0.3750
1 101.3750 -2.0000 0.0000 101.3750 2.0000 0.0000 1.1
1 101.3750 2.0000 0.0000 101.3750 24.0625 0.0000 0.3750
1 113.3750 -24.0625 0.0000 113.3750 -2.0000 0.0000 0.3750
1 113.3750 -2.0000 0.0000 113.3750 2.0000 0.0000 1.1
1 113.3750 2.0000 0.0000 113.3750 24.0625 0.0000 0.3750
1 125.3750 -24.0625 0.0000 125.3750 -2.0000 0.0000 0.3750
1 125.3750 -2.0000 0.0000 125.3750 2.0000 0.0000 1.1
1 125.3750 2.0000 0.0000 125.3750 24.0625 0.0000 0.3750
1 137.3750 -24.0625 0.0000 137.3750 -2.0000 0.0000 0.3750
1 137.3750 -2.0000 0.0000 137.3750 2.0000 0.0000 1.1
1 137.3750 2.0000 0.0000 137.3750 24.0625 0.0000 0.3750
1 de1 r 0 x1 y1 0 d
1 x1 y1 0 x2 y2 -s d
1 x2 y2 -s x3 y3 -s d
1 x3 y3 -s x4 y4 0 d
1 x4 y4 0 de2 -r 0 d
1 de1 -r 0 x1 -y1 0 d
1 x1 -y1 0 x2 -y2 s d
1 x2 -y2 s x3 -y3 s d
1 x3 -y3 s x4 -y4 0 d
1 x4 -y4 0 de2 r 0 d
1 de2 r 0 x5 y1 0 d
1 x5 y1 0 x6 y2 -s d
1 x6 y2 -s x7 y3 -s d
1 x7 y3 -s x8 y4 0 d
1 x8 y4 0 de3 -r 0 d
1 de2 -r 0 x5 -y1 0 d
1 x5 -y1 0 x6 -y2 s d
1 x6 -y2 s x7 -y3 s d
1 x7 -y3 s x8 -y4 0 d
1 x8 -y4 0 de3 r 0 d
1 de3 r 0 x9 y1 0 d
1 x9 y1 0 x10 y2 -s d
1 x10 y2 -s x11 y3 -s d
1 x11 y3 -s x12 y4 0 d
1 x12 y4 0 de4 -r 0 d
1 de3 -r 0 x9 -y1 0 d
1 x9 -y1 0 x10 -y2 s d
1 x10 -y2 s x11 -y3 s d
1 x11 -y3 s x12 -y4 0 d
1 x12 -y4 0 de4 r 0 d
1 de4 r 0 x13 y1 0 d
1 x13 y1 0 x14 y2 -s d
1 x14 y2 -s x15 y3 -s d
1 x15 y3 -s x16 y4 0 d
1 x16 y4 0 de5 -r 0 d
1 de4 -r 0 x13 -y1 0 d
1 x13 -y1 0 x14 -y2 s d
1 x14 -y2 s x15 -y3 s d
1 x15 -y3 s x16 -y4 0 d
1 x16 -y4 0 de5 r 0 d
1 de5 -r 0.0000 de5 -r -0.7500 .125 steel
1 de5 -r -0.7500 de5 r -0.7500 #18 copper
1 de5 r 0.0000 de5 r -0.7500 .125 steel
1 source
Wire 76, center
Bracket 4" x 1.625" x 1/32", modeled as a U channel by YO to get the 1.1"
equivalent diameter of the inner taper section for the parasitic elements.
The steel wires near the feedpoint model the terminal bolts.
88–108 MHz