The Antenna Performance Specialties APS-9B is a log-Yagi array with nine elements on a 97″ boom. Four of the elements are driven. A shorted transmission line terminates at a passive reflector.
I modeled the antenna with the AO 9.67 Antenna Optimizer. This image shows the antenna geometry.
This shows phasing line and feedpoint detail. I added a wire across the feedpoint terminals and placed a source at its center. The red dot is the feedpoint.
Calculated performance is for 28 analysis segments per element halfwave with additional segmentation for the phasing lines. Forward gain includes mismatch and conductor losses. F/R is the ratio of forward power to that of the worst backlobe in the rear half-plane.
Frequency Impedance SWR Mismatch Conductor Forward F/R
MHz ohms Loss dB Loss dB Gain dBd dB
88 174+j26 1.74 0.33 0.04 6.63 26.94
89 183+j29 1.66 0.28 0.04 6.71 26.94
90 191+j32 1.60 0.24 0.03 6.79 26.97
91 199+j33 1.54 0.20 0.03 6.87 26.98
92 204+j31 1.50 0.17 0.03 6.94 26.92
93 208+j27 1.47 0.16 0.03 7.02 26.80
94 209+j23 1.45 0.15 0.03 7.09 26.64
95 206+j19 1.47 0.16 0.03 7.15 26.44
96 200+j17 1.51 0.18 0.03 7.20 26.22
97 192+j19 1.58 0.22 0.03 7.24 25.99
98 183+j25 1.66 0.27 0.03 7.28 25.83
99 174+j36 1.76 0.34 0.03 7.31 25.74
100 168+j52 1.86 0.41 0.03 7.35 25.72
101 168+j74 1.94 0.47 0.03 7.41 25.69
102 176+j98 1.96 0.48 0.04 7.50 25.68
103 197+j121 1.90 0.44 0.04 7.65 24.55
104 234+j127 1.71 0.31 0.04 7.86 22.65
105 263+j86 1.39 0.12 0.05 8.08 20.50
106 199+j33 1.54 0.20 0.06 7.90 18.51
107 96.2+j89.3 3.42 1.55 0.12 6.22 16.76
108 43.7+j221 10.65 5.03 0.31 1.81 15.96
Ken Wetzel measured the return loss of his APS-9B with a spectrum analyzer, tracking generator, return-loss bridge, and halfwave coaxial balun. Raise the curve 2.5 dB to account for feedline and balun losses.
Measured and modeled return loss curves have the same general shape, including the dip at 105 MHz, but details differ significantly. Ken used a balun with a return loss of 19.5 dB at the band edges. Such a balun can affect some measurements in a way the model does not account for. To approximate the effect, the dashed red curve adds a shunt feedpoint capacitance of 1.5 pF to the model. I negated all values to match the spectrum analyzer curve.
APS-9B Free Space 98 MHz 68 6063-T832 wires, inches e1 = 35 ; boom centerline to element tips e2 = 31.075 e3 = 28.575 e4 = 25.7 e5 = 26.5 e6 = 17.39 e7 = 26 e8 = 24.875 e9 = 24.375 p1 = 0 ; element positions p2 = 12 p3 = 24 p4 = 35.94 p5 = 39.94 p6 = 47.94 p7 = 57.5 p8 = 75 p9 = 97 t = .75 ; feedpoint bolt length eqd = 1.28 ; element + mounting plate equivalent diameter d = .11 ; phasing-line diameter s = .375 / 2 ; half of phasing-line crossover spacing r = 1.875 / 2 ; half of rivet spacing for insulated elements h = 12 / 2 ; half of DE spacing a = 3.25 ; phasing-line bend start distance from rivets b = 3.75 ; bend end distance y1 = r * (1 - a / h) ; bend start y y2 = r * (1 - b / h) ; bend end y xa = p1 + a ; bend x values xb = p1 + b xc = p2 - b xd = p2 - a xe = p2 + a xf = p2 + b xg = p3 - b xh = p3 - a xi = p3 + a xj = p3 + b xk = p4 - b xl = p4 - a xm = p4 + a xn = p4 + b xo = p6 - b xp = p6 - a 1 p1 -e1 0 p1 -2 0 0.375 1 p1 -2 0 p1 -1.25 0 eqd ; rivet spacing = 2.5" 1 p1 -1.25 0 p1 1.25 0 eqd ; for metallic brackets 1 p1 1.25 0 p1 2 0 eqd 1 p1 2 0 p1 e1 0 0.375 1 p2 -e2 0 p2 -r 0 0.375 1 p2 r 0 p2 e2 0 0.375 1 p3 -e3 0 p3 -r 0 0.375 1 p3 r 0 p3 e3 0 0.375 1 p4 -e4 0 p4 -r 0 0.375 1 p4 r 0 p4 e4 0 0.375 1 p5 -e5 -2 p5 -2 -2 0.375 1 p5 -2 -2 p5 2 -2 eqd 1 p5 2 -2 p5 e5 -2 0.375 1 p6 -e6 0 p6 -r 0 0.375 1 p6 -r 0 p6 -r -t 0.125 zinc ; terminal bolt 1 p6 -r -t p6 r -t #16 copper 1 p6 r 0 p6 r -t 0.125 zinc ; terminal bolt 1 p6 r 0 p6 e6 0 0.375 1 p7 -e7 0 p7 -2 0 0.375 1 p7 -2 0 p7 2 0 eqd 1 p7 2 0 p7 e7 0 0.375 1 p8 -e8 0 p8 -2 0 0.375 1 p8 -2 0 p8 2 0 eqd 1 p8 2 0 p8 e8 0 0.375 1 p9 -e9 0 p9 -2 0 0.375 1 p9 -2 0 p9 2 0 eqd 1 p9 2 0 p9 e9 0 0.375 4 p1 1.25 0 xa y1 0 d 1 xa y1 0 xb y2 -s d 10 xb y2 -s xc -y2 -s d 1 xc -y2 -s xd -y1 0 d 4 xd -y1 0 p2 -r 0 d 4 p2 -r 0 xe -y1 0 d 1 xe -y1 0 xf -y2 s d 10 xf -y2 s xg y2 s d 1 xg y2 s xh y1 0 d 4 xh y1 0 p3 r 0 d 4 p3 r 0 xi y1 0 d 1 xi y1 0 xj y2 -s d 10 xj y2 -s xk -y2 -s d 1 xk -y2 -s xl -y1 0 d 4 xl -y1 0 p4 -r 0 d 4 p4 -r 0 xm -y1 0 d 1 xm -y1 0 xn -y2 s d 10 xn -y2 s xo y2 s d 1 xo y2 s xp y1 0 d 4 xp y1 0 p6 r 0 d 4 p1 -1.25 0 xa -y1 0 d 1 xa -y1 0 xb -y2 s d 10 xb -y2 s xc y2 s d 1 xc y2 s xd y1 0 d 4 xd y1 0 p2 r 0 d 4 p2 r 0 xe y1 0 d 1 xe y1 0 xf y2 -s d 10 xf y2 -s xg -y2 -s d 1 xg -y2 -s xh -y1 0 d 4 xh -y1 0 p3 -r 0 d 4 p3 -r 0 xi -y1 0 d 1 xi -y1 0 xj -y2 s d 10 xj -y2 s xk y2 s d 1 xk y2 s xl y1 0 d 4 xl y1 0 p4 r 0 d 4 p4 r 0 xm y1 0 d 1 xm y1 0 xn y2 -s d 10 xn y2 -s xo -y2 -s d 1 xo -y2 -s xp -y1 0 d 4 xp -y1 0 p6 -r 0 d 1 source Wire 17, center I modeled the 4" x 1.625" x 0.5" x 0.05" element mounting brackets as U-channels with the YO 8.00 Yagi Optimizer. YO calculated the equivalent cylindrical diameter as 1.28".
88–108 MHz