Antennacraft FM10

The Antennacraft FM10 is a log-Yagi array with ten elements on a 120″ boom. Three of the elements are driven.

I modeled the antenna with the AO 9.53 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.

Joe Roberts used this FM10 in the late 1970s at Wilbraham, Massachusetts.

Feedpoint

Normally I jumper a wire across the feedpoint terminals and place a source at its center. This model is unrealistic for the FM10 because the boom is between the terminals. A Radio Shack balun often used with the antenna has twin-lead split 3″ from the terminal lugs. I model this geometry instead. The resulting inductive reactance alters SWR, mismatch loss, and forward gain.

Modeling Results

Calculated performance is for 28 analysis segments per conductor halfwave with additional segments 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     199 - j33    1.54     0.20      0.03      6.96     17.38
    89     223 - j15    1.36     0.10      0.03      7.10     21.37
    90     244 - j5     1.23     0.05      0.02      7.19     23.45
    91     265 - j2     1.13     0.02      0.02      7.26     23.97
    92     286 - j5     1.05     0.00      0.02      7.35     24.14
    93     307 - j17    1.06     0.00      0.02      7.43     24.37
    94     324 - j38    1.15     0.02      0.02      7.51     24.61
    95     334 - j68    1.27     0.06      0.02      7.57     23.23
    96     330 - j106   1.42     0.13      0.02      7.62     21.44
    97     311 - j143   1.59     0.23      0.02      7.65     19.98
    98     277 - j170   1.80     0.37      0.02      7.65     18.77
    99     234 - j182   2.05     0.54      0.02      7.60     17.74
   100     194 - j180   2.31     0.74      0.03      7.54     16.83
   101     160 - j168   2.60     0.96      0.03      7.46     15.98
   102     136 - j149   2.86     1.15      0.03      7.40     15.32
   103     119 - j129   3.05     1.28      0.03      7.37     14.80
   104     110 - j108   3.12     1.33      0.03      7.42     14.44
   105     109 - j90    3.02     1.27      0.03      7.58     14.29
   106     117 - j79    2.77     1.08      0.03      7.84     14.44
   107     129 - j83    2.55     0.92      0.03      8.06     14.96
   108     126 - j109   2.76     1.07      0.04      7.94     16.04

Antenna File

Antennacraft FM10
Free Space
98.000 MHz
52 6063-T832 wires, inches
de1 = 14.625			; driven element locations
de2 = 27
de3 = 39.375
d = .11				; phasing-line diameter
r = 3 / 2			; half of rivet spacing (insulated elements)
h = 12.375 / 2			; half of DE spacing
y1 = r * (1 - 3.375 / h)	; y at first phasing-line bend
y2 = r * (1 - 3.875 / h)	; y at second bend
y3 = -y2			; y at third bend
y4 = -y1			; y at fourth bend
x1 = de1 + 3.375		; x at first phasing-line bend, rear line
x2 = de1 + 3.875		; x at second bend
x3 = de2 - 3.875		; x at third bend
x4 = de2 - 3.375		; x at fourth bend
x5 = de2 + 3.375		; x at first phasing-line bend, forward line
x6 = de2 + 3.875		; x at second bend
x7 = de3 - 3.875		; x at third bend
x8 = de3 - 3.375		; x at fourth bend
s = .5 / 2			; half of phasing-line crossover spacing
f = .3125 / 2			; feedpoint half-spacing
b = .75				; feedpoint bolt length
v = b + 3			; feedpoint

1      0.0000  -32.8750    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   32.8750    0.0000    0.3750

1     14.6250  -29.5000    0.0000     14.6250   -r         0.0000    0.3750
1     14.6250    r         0.0000     14.6250   29.5000    0.0000    0.3750

1     27.0000  -28.2500    0.0000     27.0000   -r         0.0000    0.3750
1     27.0000    r         0.0000     27.0000   28.2500    0.0000    0.3750

1     39.3750  -21.8750    0.0000     39.3750   -r         0.0000    0.3750
1     39.3750    r         0.0000     39.3750   21.8750    0.0000    0.3750

1     43.1250  -25.0000   -1.9375     43.1250   -2.0000   -1.9375    0.3750
1     43.1250   -2.0000   -1.9375     43.1250    2.0000   -1.9375    1.1
1     43.1250    2.0000   -1.9375     43.1250   25.0000   -1.9375    0.3750

1     53.7500  -24.0000    0.0000     53.7500   -2.0000    0.0000    0.3750
1     53.7500   -2.0000    0.0000     53.7500    2.0000    0.0000    1.1
1     53.7500    2.0000    0.0000     53.7500   24.0000    0.0000    0.3750

1     65.2500  -24.0000    0.0000     65.2500   -2.0000    0.0000    0.3750
1     65.2500   -2.0000    0.0000     65.2500    2.0000    0.0000    1.1
1     65.2500    2.0000    0.0000     65.2500   24.0000    0.0000    0.3750

1     83.7500  -24.0000    0.0000     83.7500   -2.0000    0.0000    0.3750
1     83.7500   -2.0000    0.0000     83.7500    2.0000    0.0000    1.1
1     83.7500    2.0000    0.0000     83.7500   24.0000    0.0000    0.3750

1    100.3750  -24.0000    0.0000    100.3750   -2.0000    0.0000    0.3750
1    100.3750   -2.0000    0.0000    100.3750    2.0000    0.0000    1.1
1    100.3750    2.0000    0.0000    100.3750   24.0000    0.0000    0.3750

1    117.3750  -24.0000    0.0000    117.3750   -2.0000    0.0000    0.3750
1    117.3750   -2.0000    0.0000    117.3750    2.0000    0.0000    1.1
1    117.3750    2.0000    0.0000    117.3750   24.0000    0.0000    0.3750
				  
4     de1        r         0          x1        y1         0         d 
1      x1       y1         0          x2        y2        -s         d 
10     x2       y2         -s         x3        y3        -s         d 
1      x3       y3         -s         x4        y4         0         d 
4      x4       y4         0         de2        -r         0         d 
4     de1       -r         0          x1        -y1        0         d 
1      x1      -y1         0          x2        -y2        s         d 
10     x2      -y2         s          x3        -y3        s         d 
1      x3      -y3         s          x4        -y4        0         d 
4      x4      -y4         0         de2         r         0         d 
4     de2        r         0          x5        y1         0         d 
1      x5       y1         0          x6        y2         s         d 
8      x6       y2         s          x7        y3         s         d 
1      x7       y3         s          x8        y4         0         d 
4      x8       y4         0         de3        -r         0         d 
4     de2       -r         0          x5        -y1        0         d 
1      x5      -y1         0          x6        -y2       -s         d 
8      x6      -y2        -s          x7        -y3       -s         d 
1      x7      -y3        -s          x8        -y4        0         d 
4      x8      -y4         0         de3         r         0         d 

1     de3       -r         0         de3        -r        -b        .125    zinc
1     de3       -r        -b         de3        -f        -v         #18    copper
1     de3        f        -v         de3        -f        -v         #18    copper
1     de3        r        -b         de3         f        -v         #18    copper
1     de3        r         0         de3         r        -b        .125    zinc
1 source
Wire 50, center

The 4" x 1.625" x 1/32" bracket was modeled as a U channel by YO to get the
1.1" equivalent diameter of the inner taper section for the parasitic elements.

September 7, 201388108 MHz