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-Pro 8.50 Antenna Optimizer program. This image shows the antenna geometry.
This image shows segmentation detail for the phasing lines that interconnect the driven elements. The red dot is the feedpoint.
Ken Wetzel measured the return loss of his APS-9B with a spectrum analyzer, tracking generator, return-loss bridge, and halfwave balun. Add 2.5 dB to the figures shown to account for feedline and balun losses. The 5 dB return loss at 108 MHz corresponds to an SWR of 3.57.
I modeled the APS-9B element mounting brackets as U-channels with the YO 7.70 Yagi Optimizer. YO calculated their equivalent cylindrical diameter as 1.1″. However, this value yielded very high SWR at 108 MHz. Using 3″ instead gives a value close to what Ken measured. I used this equivalent diameter in the model even though I see no physical justification for such a large value.
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. Balun loss is not included; subtract 0.75 from the gain figures to account for it.
88.000 MHz: Impedance 168 + j27 ohms
SWR 1.81
Mismatch Loss 0.38 dB
Wire Loss 0.05 dB
Mismatched Gain 6.55 dBd
F/R 26.92 dB
93.000 MHz: Impedance 205 + j31 ohms
SWR 1.49
Mismatch Loss 0.17 dB
Wire Loss 0.03 dB
Mismatched Gain 6.97 dBd
F/R 26.85 dB
98.000 MHz: Impedance 187 + j28 ohms
SWR 1.62
Mismatch Loss 0.25 dB
Wire Loss 0.03 dB
Mismatched Gain 7.26 dBd
F/R 25.61 dB
103.000 MHz: Impedance 199 + j115 ohms
SWR 1.85
Mismatch Loss 0.41 dB
Wire Loss 0.04 dB
Mismatched Gain 7.65 dBd
F/R 25.72 dB
108.000 MHz: Impedance 93.2 + j105 ohms
SWR 3.65
Mismatch Loss 1.70 dB
Wire Loss 0.13 dB
Mismatched Gain 6.16 dBd
F/R 15.42 dB
APS-9B Free Space 98 MHz 68 6063-T832 wires, inches e1 = 35 ; boom centerline to element tips e2 = 31 e3 = 28.625 e4 = 25.75 e5 = 26.5 e6 = 17.5 e7 = 26 e8 = 24.875 e9 = 24.375 p1 = 0 ; element positions p2 = 12 p3 = 24 p4 = 36 p5 = 40 p6 = 48 p7 = 57.5 p8 = 75 p9 = 97 eqd = 3 ; bracket equivalent diameter, calculated as 1.1 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 ; x values for all bends 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 -0.75 0.125 steel 1 p6 -r -0.75 p6 r -0.75 #18 copper 1 p6 r 0 p6 r -0.75 0.125 steel 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 1 p1 1.25 0 xa y1 0 d 1 xa y1 0 xb y2 -s d 1 xb y2 -s xc -y2 -s d 1 xc -y2 -s xd -y1 0 d 1 xd -y1 0 p2 -r 0 d 1 p2 -r 0 xe -y1 0 d 1 xe -y1 0 xf -y2 s d 1 xf -y2 s xg y2 s d 1 xg y2 s xh y1 0 d 1 xh y1 0 p3 r 0 d 1 p3 r 0 xi y1 0 d 1 xi y1 0 xj y2 -s d 1 xj y2 -s xk -y2 -s d 1 xk -y2 -s xl -y1 0 d 1 xl -y1 0 p4 -r 0 d 1 p4 -r 0 xm -y1 0 d 1 xm -y1 0 xn -y2 s d 1 xn -y2 s xo y2 s d 1 xo y2 s xp y1 0 d 1 xp y1 0 p6 r 0 d 1 p1 -1.25 0 xa -y1 0 d 1 xa -y1 0 xb -y2 s d 1 xb -y2 s xc y2 s d 1 xc y2 s xd y1 0 d 1 xd y1 0 p2 r 0 d 1 p2 r 0 xe y1 0 d 1 xe y1 0 xf y2 -s d 1 xf y2 -s xg -y2 -s d 1 xg -y2 -s xh -y1 0 d 1 xh -y1 0 p3 -r 0 d 1 p3 -r 0 xi -y1 0 d 1 xi -y1 0 xj -y2 s d 1 xj -y2 s xk y2 s d 1 xk y2 s xl y1 0 d 1 xl y1 0 p4 r 0 d 1 p4 r 0 xm y1 0 d 1 xm y1 0 xn y2 -s d 1 xn y2 -s xo -y2 -s d 1 xo -y2 -s xp -y1 0 d 1 xp -y1 0 p6 -r 0 d 1 source Wire 17, center I modeled the 4" x 1.625" x 0.5" x 1/32" metallic element-mounting brackets as U-channels with the YO 7.70 Yagi Optimizer. YO calculated the equivalent cylindrical diameter as 1.1", but I used 3" because this made SWR at 108 MHz agree with measurement. The 0.75" conductors near the feedpoint model the terminal bolts.
88–108 MHz