Antennacraft FM13

The Antennacraft FM13 is a log-Yagi array with 13 elements on a 137″ boom. Five of the elements are driven. A review is here.

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.

Feedpoint

Normally I jumper a wire across the feedpoint terminals and place a source at its center. This model is unrealistic for the FM13 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     288 + j59    1.23     0.05      0.06      8.21     19.98
    89     270 + j51    1.23     0.05      0.06      8.37     19.59
    90     264 + j41    1.21     0.04      0.06      8.51     19.50
    91     255 + j24    1.20     0.04      0.05      8.63     19.81
    92     236 + j12    1.28     0.06      0.05      8.68     20.57
    93     215 + j14    1.40     0.12      0.05      8.69     21.75
    94     200 + j26    1.52     0.19      0.04      8.68     23.32
    95     197 + j44    1.58     0.22      0.04      8.68     24.63
    96     208 + j62    1.56     0.21      0.04      8.74     25.52
    97     234 + j73    1.45     0.15      0.04      8.85     26.08
    98     273 + j65    1.28     0.07      0.04      8.97     24.13
    99     310 + j21    1.08     0.01      0.04      9.08     21.89
   100     310 - j51    1.19     0.03      0.03      9.11     19.80
   101     257 - j108   1.51     0.19      0.03      9.00     17.92
   102     190 - j118   1.94     0.47      0.03      8.73     16.43
   103     141 - j97    2.41     0.82      0.03      8.38     15.21
   104     111 - j66    2.84     1.14      0.03      8.01     14.23
   105    97.9 - j32.5  3.11     1.33      0.03      7.75     13.49
   106    98.2 + j1.4   3.05     1.29      0.03      7.69     13.02
   107     116 + j34    2.62     0.97      0.04      7.90     12.83
   108     168 + j54    1.86     0.42      0.04      8.33     12.98

Antenna File

Antennacraft FM13
Free Space
98.000 MHz
79 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
f = .3125 / 2			; feedpoint half-spacing
b = .75				; feedpoint bolt length
v = b + 3			; feedpoint

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
				  
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 
10     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 
10     x6      -y2         s          x7        -y3        s         d 
1      x7      -y3         s          x8        -y4        0         d 
4      x8      -y4         0         de3         r         0         d 
4     de3        r         0          x9        y1         0         d 
1      x9       y1         0          x10       y2        -s         d 
10     x10      y2         -s         x11       y3        -s         d 
1      x11      y3         -s         x12       y4         0         d 
4      x12      y4         0         de4        -r         0         d 
4     de3       -r         0          x9        -y1        0         d 
1      x9      -y1         0          x10       -y2        s         d 
10     x10     -y2         s          x11       -y3        s         d 
1      x11     -y3         s          x12       -y4        0         d 
4      x12     -y4         0         de4         r         0         d 
4     de4        r         0          x13       y1         0         d 
1      x13      y1         0          x14       y2        -s         d 
10     x14      y2         -s         x15       y3        -s         d 
1      x15      y3         -s         x16       y4         0         d 
4      x16      y4         0         de5        -r         0         d 
4     de4       -r         0          x13       -y1        0         d 
1      x13     -y1         0          x14       -y2        s         d 
10     x14     -y2         s          x15       -y3        s         d 
1      x15     -y3         s          x16       -y4        0         d 
4      x16     -y4         0         de5         r         0         d 

1     de5       -r         0         de5        -r        -b        .125    zinc
1     de5       -r        -b         de5        -f        -v         #18    copper
1     de5        f        -v         de5        -f        -v         #18    copper
1     de5        r        -b         de5         f        -v         #18    copper
1     de5        r         0         de5         r        -b        .125    zinc

1 source
Wire 77, 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.

August 28, 201688108 MHz