Antenna Performance Specialties APS-9B

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.

Modeling Results

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

Measurements

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.

Antenna File

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".

July 13, 201888108 MHz