Metric Yagis

These five Yagis with booms two to six meters long use metric dimensions. Each design maximizes forward gain while keeping all backlobes at least 30 dB down over 87.5–108 MHz. The Yagis use a driven element loop that couples to the first director in a way that greatly improves the pattern. I optimized all designs with the AO 9.65 Antenna Optimizer.

Two-Meter Yagi

This antenna has eight elements on a two-meter boom. The red dot is the 75Ω feedpoint, which has a small series capacitor.

Modeling Results

Calculated performance is for 28 analysis segments per conductor halfwave. 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 
     87.5    67.3+j6.6    1.15     0.02      0.02      5.83      30.01  
    88     69.7+j3.0    1.09     0.01      0.02      5.85      33.02
    89     71.6-j2.3    1.06     0.00      0.02      5.89      31.98
    90     71.8-j4.7    1.08     0.01      0.02      5.93      30.98
    91     72.1-j5.3    1.09     0.01      0.02      5.99      30.30
    92     73.0-j4.6    1.07     0.00      0.02      6.06      30.01
    93     74.4-j3.9    1.05     0.00      0.02      6.14      29.94
    94     76.7-j3.2    1.05     0.00      0.02      6.24      30.08
    95     79.4-j3.2    1.07     0.01      0.02      6.33      30.37
    96     82.3-j4.0    1.11     0.01      0.02      6.43      30.33
    97     85.1-j6.0    1.16     0.02      0.02      6.53      30.22
    98     87.3-j9.1    1.21     0.04      0.02      6.63      30.14
    99     88.4-j13.3   1.26     0.06      0.02      6.73      30.04
   100     88.1-j18.6   1.32     0.08      0.02      6.83      30.01
   101     85.6-j24.4   1.39     0.12      0.02      6.92      30.04
   102     80.0-j30.0   1.48     0.16      0.02      6.99      30.06
   103     72.0-j33.8   1.58     0.23      0.03      7.04      30.24
   104     62.1-j34.6   1.71     0.31      0.03      7.05      30.73
   105     52.1-j30.8   1.83     0.39      0.04      7.03      30.52
   106     45.4-j22.1   1.86     0.41      0.05      7.02      30.01
   107     49.0-j9.2    1.57     0.22      0.07      7.13      30.00
   108     95.8-j30.7   1.54     0.20      0.14      6.80      30.00

Antenna File

Two-Meter Yagi
Free Space Symmetric
87.5 90 92 95 98 100 102 104 105 106 107 108 MHz
13 6063-T832 wires, meters
h = .33148386		; reflector height
rp = 0			; element positions
dep = .32403963
d1p = .5089447
d2p = .6648566
d3p = 1.0631633
d4p = 1.3091594
d5p = 2
r = .8995709		; element half-lengths
de = .7865902
d1 = .6754952
d2 = .66206912
d3 = .6179316
d4 = .59579233
d5 = .5510639
w = .062135155		; loop half-width (one side of center)
s = .14489323		; loop side
p = dep + s
1     rp  -r  h     rp   r  h    .01
1     rp  -r -h     rp   r -h    .01
1    dep   w  0    dep  de  0    .01
1    dep  -w  0    dep -de  0    .01
6    dep  -w  0    dep   w  0    .01
6      p  -w  0      p   w  0    .01
7      p   w  0    dep   w  0    .01
7      p  -w  0    dep  -w  0    .01
1    d1p -d1  0    d1p  d1  0    .01
1    d2p -d2  0    d2p  d2  0    .01
1    d3p -d3  0    d3p  d3  0    .01
1    d4p -d4  0    d4p  d4  0    .01
1    d5p -d5  0    d5p  d5  0    .01
1 source
Wire 6, center
1 load
c = 8.85914		; series feedpoint capacitor
Wire 6, center c pF

Sensitivity Analysis

The following table shows the largest performance degradation over 87.5, 93, 98, 103, and 108 MHz in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
     h   0.0010   0.00   0.13
    rp   0.0010   0.00   0.10
   dep   0.0010   0.02   0.20
   d1p   0.0010   0.05   0.17
   d2p   0.0010   0.03   0.14
   d3p   0.0010   0.00   0.13
   d4p   0.0010   0.00   0.08
   d5p   0.0010   0.00   0.07
     r   0.0005   0.00   0.26
    de   0.0005   0.00   0.07
    d1   0.0005   0.05   0.66
    d2   0.0005   0.15   1.10
    d3   0.0005   0.01   0.28
    d4   0.0005   0.00   0.21
    d5   0.0005   0.00   0.12
     w   0.0005   0.01   0.00
     s   0.0010   0.01   0.11
     c   0.8859   0.31   0.00

Three-Meter Yagi

This antenna has ten elements on a three-meter boom.

Modeling Results

Calculated performance is for 28 analysis segments per conductor halfwave. 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 
     87.5    71.9+j5.8    1.12     0.01      0.02      7.08      30.00  
    88     75.4+j2.1    1.03     0.00      0.02      7.12      30.33
    89     78.3-j4.5    1.08     0.01      0.02      7.19      30.89
    90     77.5-j8.2    1.12     0.01      0.02      7.27      31.29
    91     75.6-j9.0    1.13     0.02      0.02      7.37      31.70
    92     74.0-j7.4    1.11     0.01      0.02      7.48      31.30
    93     73.2-j4.2    1.06     0.00      0.02      7.61      30.65
    94     73.6-j0.0    1.02     0.00      0.02      7.74      30.21
    95     75.7+j4.2    1.06     0.00      0.02      7.87      30.00
    96     79.2+j8.2    1.13     0.02      0.02      7.99      30.03
    97     84.2+j11.1   1.20     0.04      0.02      8.12      30.34
    98     90.1+j12.2   1.27     0.06      0.02      8.24      30.74
    99     96.0+j10.2   1.32     0.08      0.02      8.36      31.47
   100      100+j6      1.35     0.10      0.02      8.49      32.15
   101      101-j0      1.35     0.10      0.02      8.62      31.51
   102     98.4-j5.4    1.32     0.08      0.03      8.74      30.75
   103     94.6-j7.1    1.28     0.07      0.03      8.84      30.19
   104     92.3-j6.2    1.25     0.05      0.03      8.89      30.00
   105     93.8-j7.5    1.27     0.06      0.04      8.85      30.00
   106     92.8-j15.9   1.33     0.09      0.05      8.69      30.15
   107     79.3-j18.0   1.27     0.06      0.06      8.42      30.48
   108     77.2+j7.7    1.11     0.01      0.09      7.98      30.00

Antenna File

Three-Meter Yagi
Free Space Symmetric
87.5 90 92 95 97 102 104 105 106 107 108 MHz
15 6063-T832 wires, meters
h = .5936546		; outer reflector height
rp = 0			; element positions
dep = .43079176
d1p = .64241151
d2p = .923438
d3p = 1.3318776
d4p = 1.670833
d5p = 2.2196736
d6p = 3
ro = .9211657		; outer reflector half-length
ri = .92941854		; inner reflector half-length
de = .7777548		; driven element half-length
d1 = .6591962		; director half-lengths
d2 = .6485328
d3 = .631916
d4 = .62899653
d5 = .6248731
d6 = .56236
w = .063599702		; loop half-width (one side of center)
s = .17045478		; loop side
p = dep + s
1     rp -ro  h     rp  ro  h    .01
1     rp -ri  0     rp  ri  0    .01
1     rp -ro -h     rp  ro -h    .01
1    dep   w  0    dep  de  0    .01
1    dep  -w  0    dep -de  0    .01
6    dep  -w  0    dep   w  0    .01
6      p  -w  0      p   w  0    .01
7      p   w  0    dep   w  0    .01
7      p  -w  0    dep  -w  0    .01
1    d1p -d1  0    d1p  d1  0    .01
1    d2p -d2  0    d2p  d2  0    .01
1    d3p -d3  0    d3p  d3  0    .01
1    d4p -d4  0    d4p  d4  0    .01
1    d5p -d5  0    d5p  d5  0    .01
1    d6p -d6  0    d6p  d6  0    .01
1 source
Wire 7, center
1 load
c = 7.646869		; series feedpoint capacitor
Wire 7, center c pF

Sensitivity Analysis

The following table shows the largest performance degradation over 87.5, 93, 98, 103, and 108 MHz in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
     h   0.0010   0.00   0.05
    rp   0.0010   0.00   0.03
   dep   0.0010   0.01   0.17
   d1p   0.0010   0.01   0.23
   d2p   0.0010   0.00   0.21
   d3p   0.0010   0.00   0.23
   d4p   0.0010   0.00   0.21
   d5p   0.0010   0.00   0.23
   d6p   0.0010   0.00   0.06
    ro   0.0005   0.00   0.10
    ri   0.0005   0.00   0.06
    de   0.0005   0.00   0.06
    d1   0.0005   0.01   0.04
    d2   0.0005   0.03   0.38
    d3   0.0005   0.01   0.45
    d4   0.0005   0.02   0.48
    d5   0.0005   0.01   0.16
    d6   0.0005   0.00   0.04
     w   0.0005   0.01   0.00
     s   0.0010   0.01   0.09
     c   0.7647   0.16   0.00

Four-Meter Yagi

This antenna has 12 elements on a four-meter boom.

Modeling Results

Calculated performance is for 28 analysis segments per conductor halfwave. 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 
     87.5    66.1+j2.0    1.14     0.02      0.02      7.73      30.01  
    88     67.8-j1.0    1.11     0.01      0.02      7.78      32.40
    89     68.4-j5.0    1.12     0.01      0.02      7.88      31.46
    90     67.3-j6.4    1.15     0.02      0.02      7.99      30.72
    91     66.1-j5.5    1.16     0.02      0.02      8.11      30.24
    92     65.4-j3.3    1.16     0.02      0.02      8.25      30.04
    93     65.3-j0.1    1.15     0.02      0.02      8.40      30.05
    94     66.1+j3.4    1.14     0.02      0.02      8.56      30.16
    95     67.9+j6.8    1.15     0.02      0.02      8.72      30.44
    96     70.5+j10.1   1.16     0.02      0.02      8.89      30.01
    97     74.0+j12.6   1.18     0.03      0.02      9.06      29.85
    98     78.3+j13.9   1.20     0.04      0.02      9.22      30.01
    99     83.1+j13.3   1.22     0.04      0.02      9.39      30.79
   100     86.8+j9.9    1.21     0.04      0.02      9.54      31.76
   101     88.4+j3.5    1.19     0.03      0.03      9.68      31.66
   102     84.7-j2.8    1.14     0.02      0.03      9.80      31.31
   103     76.6-j5.3    1.08     0.01      0.03      9.86      30.87
   104     69.0-j2.5    1.10     0.01      0.04      9.84      30.56
   105     65.8+j4.1    1.15     0.02      0.05      9.71      30.14
   106     69.3+j8.5    1.15     0.02      0.06      9.45      30.01
   107     72.1+j7.4    1.11     0.01      0.07      9.01      30.04
   108     85.2+j15.8   1.27     0.06      0.11      8.37      30.00

Antenna File

Four-Meter Yagi
Free Space Symmetric
87.5 90 92 96 98 102 104 105 106 107.3 108 MHz
17 6063-T832 wires, meters
h = .662275		; outer reflector height
rp = 0			; element positions
dep = .42542764
d1p = .6497597
d2p = .92435173
d3p = 1.3558378
d4p = 1.6891916
d5p = 2.210484
d6p = 2.7830176
d7p = 3.297144
d8p = 4
ro = .9587851		; outer reflector half-length
ri = .8920225		; inner reflector half-length
de = .78423271		; driven element half-length
d1 = .66296		; director half-lengths
d2 = .65120224
d3 = .6303252
d4 = .6268042
d5 = .633065
d6 = .6152197
d7 = .5906129
d8 = .5427582
w = .057672142		; loop half-width (one side of center)
s = .18430494		; loop side
p = dep + s
1     rp -ro  h     rp  ro  h    .01
1     rp -ri  0     rp  ri  0    .01
1     rp -ro -h     rp  ro -h    .01
1    dep   w  0    dep  de  0    .01
1    dep  -w  0    dep -de  0    .01
6    dep  -w  0    dep   w  0    .01
6      p  -w  0      p   w  0    .01
7      p   w  0    dep   w  0    .01
7      p  -w  0    dep  -w  0    .01
1    d1p -d1  0    d1p  d1  0    .01
1    d2p -d2  0    d2p  d2  0    .01
1    d3p -d3  0    d3p  d3  0    .01
1    d4p -d4  0    d4p  d4  0    .01
1    d5p -d5  0    d5p  d5  0    .01
1    d6p -d6  0    d6p  d6  0    .01
1    d7p -d7  0    d7p  d7  0    .01
1    d8p -d8  0    d8p  d8  0    .01
1 source
Wire 7, center
1 load
c = 7.874907		; series feedpoint capacitor
Wire 7, center c pF

Sensitivity Analysis

The following table shows the largest performance degradation over 87.5, 93, 98, 103, and 108 MHz in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
     h   0.0010   0.00   0.06
    rp   0.0010   0.00   0.05
   dep   0.0010   0.01   0.08
   d1p   0.0010   0.01   0.16
   d2p   0.0010   0.00   0.13
   d3p   0.0010   0.01   0.07
   d4p   0.0010   0.00   0.05
   d5p   0.0010   0.01   0.11
   d6p   0.0010   0.00   0.10
   d7p   0.0010   0.00   0.05
   d8p   0.0010   0.00   0.02
    ro   0.0005   0.00   0.04
    ri   0.0005   0.00   0.16
    de   0.0005   0.00   0.03
    d1   0.0005   0.02   0.07
    d2   0.0005   0.02   0.53
    d3   0.0005   0.01   0.16
    d4   0.0005   0.02   0.15
    d5   0.0005   0.04   0.27
    d6   0.0005   0.00   0.13
    d7   0.0005   0.00   0.13
    d8   0.0005   0.00   0.08
     w   0.0005   0.01   0.00
     s   0.0010   0.01   0.05
     c   0.7875   0.16   0.00

Five-Meter Yagi

This antenna has 15 elements on a five-meter boom.

Modeling Results

Calculated performance is for 28 analysis segments per conductor halfwave. 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 
     87.5    77.7+j7.9    1.11     0.01      0.02      8.61      30.01  
    88     81.2+j3.9    1.10     0.01      0.02      8.68      30.22
    89     83.9-j3.2    1.13     0.02      0.02      8.82      30.60
    90     82.8-j7.4    1.15     0.02      0.02      8.96      30.98
    91     80.8-j8.4    1.14     0.02      0.02      9.12      31.46
    92     79.2-j7.1    1.11     0.01      0.02      9.29      30.82
    93     79.0-j4.3    1.08     0.01      0.02      9.47      30.33
    94     79.8-j1.4    1.07     0.00      0.02      9.64      30.11
    95     82.1+j1.2    1.10     0.01      0.02      9.82      30.00
    96     85.4+j2.6    1.14     0.02      0.02      9.98      30.10
    97     88.8+j2.3    1.19     0.03      0.02     10.14      30.36
    98     91.4+j0.3    1.22     0.04      0.02     10.29      30.89
    99     92.5-j3.1    1.24     0.05      0.02     10.43      31.39
   100     91.6-j6.8    1.24     0.05      0.03     10.55      31.92
   101     89.1-j10.8   1.24     0.05      0.03     10.64      30.70
   102     84.2-j13.8   1.23     0.05      0.03     10.67      30.00
   103     76.3-j15.3   1.22     0.04      0.04     10.63      30.11
   104     67.5-j12.2   1.22     0.04      0.04     10.50      30.35
   105     62.7-j4.2    1.21     0.04      0.05     10.27      30.10
   106     66.5+j3.3    1.14     0.02      0.07      9.95      30.11
   107     74.2-j0.1    1.01     0.00      0.09      9.59      30.15
   108     92.0-j5.4    1.24     0.05      0.13      9.31      30.00

Antenna File

Five-Meter Yagi
Free Space Symmetric
87.5 90 92 95 98 100 101 102 104 105 106 107.3 108 MHz
20 6063-T832 wires, meters
h = .64018831		; outer reflector height
rp = 0			; element positions
dep = .49362727
d1p = .7323495
d2p = .9825406
d3p = 1.3258083
d4p = 1.5986318
d5p = 1.88034
d6p = 2.3715476
d7p = 2.901946
d8p = 3.339485
d9p = 3.8708207
d10p = 4.292037
d11p = 5
ro = .9131784		; outer reflector half-length
ri = .9172915		; inner reflector half-length
de = .777831		; driven element half-length
d1 = .6636809		; director half-lengths
d2 = .6560028
d3 = .6412648
d4 = .6248576
d5 = .625728
d6 = .6240153
d7 = .59576843
d8 = .6129011
d9 = .6009722
d10 = .60116664
d11 = .5691937
w = .064433102		; loop half-width (one side of center)
s = .17888163		; loop side
p = dep + s
1     rp -ro  h     rp  ro  h    .01
1     rp -ri  0     rp  ri  0    .01
1     rp -ro -h     rp  ro -h    .01
1    dep   w  0    dep  de  0    .01
1    dep  -w  0    dep -de  0    .01
6    dep  -w  0    dep   w  0    .01
6      p  -w  0      p   w  0    .01
8      p   w  0    dep   w  0    .01
8      p  -w  0    dep  -w  0    .01
1    d1p -d1  0    d1p  d1  0    .01
1    d2p -d2  0    d2p  d2  0    .01
1    d3p -d3  0    d3p  d3  0    .01
1    d4p -d4  0    d4p  d4  0    .01
1    d5p -d5  0    d5p  d5  0    .01
1    d6p -d6  0    d6p  d6  0    .01
1    d7p -d7  0    d7p  d7  0    .01
1    d8p -d8  0    d8p  d8  0    .01
1    d9p -d9  0    d9p  d9  0    .01
1   d10p -d10 0   d10p  d10 0    .01
1   d11p -d11 0   d11p  d11 0    .01
1 source
Wire 7, center
1 load
c = 7.467456		; series feedpoint capacitor
Wire 7, center c pF

Sensitivity Analysis

The following table shows the largest performance degradation over 87.5, 93, 98, 103, and 108 MHz in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
     h   0.0010   0.00   0.06
    rp   0.0010   0.00   0.05
   dep   0.0010   0.01   0.11
   d1p   0.0010   0.01   0.11
   d2p   0.0010   0.00   0.08
   d3p   0.0010   0.00   0.06
   d4p   0.0010   0.00   0.08
   d5p   0.0010   0.00   0.07
   d6p   0.0010   0.00   0.14
   d7p   0.0010   0.00   0.10
   d8p   0.0010   0.00   0.04
   d9p   0.0010   0.00   0.08
  d10p   0.0010   0.00   0.14
  d11p   0.0010   0.00   0.10
    ro   0.0005   0.00   0.08
    ri   0.0005   0.00   0.08
    de   0.0005   0.00   0.04
    d1   0.0005   0.01   0.15
    d2   0.0005   0.03   0.39
    d3   0.0005   0.01   0.17
    d4   0.0005   0.01   0.05
    d5   0.0005   0.00   0.21
    d6   0.0005   0.01   0.12
    d7   0.0005   0.00   0.08
    d8   0.0005   0.01   0.26
    d9   0.0005   0.00   0.19
   d10   0.0005   0.00   0.06
   d11   0.0005   0.00   0.05
     w   0.0005   0.01   0.00
     s   0.0010   0.01   0.05
     c   0.7467   0.23   0.00

Six-Meter Yagi

This antenna has 17 elements on a six-meter boom.

Modeling Results

Calculated performance is for 28 analysis segments per conductor halfwave. 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 
     87.5    73.3+j5.8    1.08     0.01      0.02      9.20      30.00  
    88     77.6+j1.9    1.04     0.00      0.02      9.28      31.26
    89     81.5-j6.2    1.12     0.01      0.02      9.43      30.65
    90     81.1-j12.0   1.19     0.03      0.02      9.59      30.27
    91     78.5-j14.9   1.22     0.04      0.02      9.76      30.03
    92     75.3-j15.1   1.22     0.04      0.02      9.94      29.93
    93     72.9-j12.9   1.19     0.03      0.02     10.15      30.01
    94     71.4-j9.9    1.15     0.02      0.02     10.35      30.20
    95     71.6-j6.1    1.10     0.01      0.02     10.55      30.21
    96     73.3-j2.6    1.04     0.00      0.02     10.75      30.20
    97     76.2-j0.5    1.02     0.00      0.02     10.92      30.45
    98     79.2-j0.1    1.06     0.00      0.02     11.07      30.83
    99     80.9-j1.5    1.08     0.01      0.03     11.18      31.31
   100     81.0-j3.2    1.09     0.01      0.03     11.26      31.69
   101     80.5-j4.8    1.10     0.01      0.03     11.28      32.37
   102     79.3-j6.7    1.11     0.01      0.04     11.22      31.17
   103     76.8-j10.8   1.15     0.02      0.05     11.06      30.26
   104     68.1-j12.2   1.22     0.04      0.05     10.79      30.07
   105     61.0-j4.5    1.24     0.05      0.07     10.47      30.19
   106     68.3+j3.5    1.11     0.01      0.09     10.21      30.00
   107     71.7-j7.9    1.12     0.01      0.11     10.13      29.93
   108     91.5-j6.2    1.24     0.05      0.19     10.19      30.03

Antenna File

Six-Meter Yagi
Free Space Symmetric
87.5 93 95 98 100 101 102 103 104 105.3 106 107.3 108 MHz
22 6063-T832 wires, meters
h = .68362281		; outer reflector height
rp = 0			; element positions
dep = .49160462
d1p = .7263994
d2p = .9678485
d3p = 1.2847776
d4p = 1.5663208
d5p = 1.845225
d6p = 2.3067593
d7p = 2.7117047
d8p = 3.2256264
d9p = 3.7472078
d10p = 4.320997
d11p = 4.845762
d12p = 5.2749045
d13p = 6
ro = .9077651		; outer reflector half-length
ri = .9033324		; inner reflector half-length
de = .77851162		; driven element half-length
d1 = .66408083		; director half-lengths
d2 = .6608845
d3 = .65576074
d4 = .634097
d5 = .6372006
d6 = .6252573
d7 = .6117205
d8 = .6119818
d9 = .59872363
d10 = .61072752
d11 = .58825842
d12 = .6028955
d13 = .5670971
w = .062436035		; loop half-width (one side of center)
s = .1758659		; loop side
p = dep + s
1     rp -ro  h     rp  ro  h    .01
1     rp -ri  0     rp  ri  0    .01
1     rp -ro -h     rp  ro -h    .01
1    dep   w  0    dep  de  0    .01
1    dep  -w  0    dep -de  0    .01
6    dep  -w  0    dep   w  0    .01
6      p  -w  0      p   w  0    .01
8      p   w  0    dep   w  0    .01
8      p  -w  0    dep  -w  0    .01
1    d1p -d1  0    d1p  d1  0    .01
1    d2p -d2  0    d2p  d2  0    .01
1    d3p -d3  0    d3p  d3  0    .01
1    d4p -d4  0    d4p  d4  0    .01
1    d5p -d5  0    d5p  d5  0    .01
1    d6p -d6  0    d6p  d6  0    .01
1    d7p -d7  0    d7p  d7  0    .01
1    d8p -d8  0    d8p  d8  0    .01
1    d9p -d9  0    d9p  d9  0    .01
1   d10p -d10 0   d10p  d10 0    .01
1   d11p -d11 0   d11p  d11 0    .01
1   d12p -d12 0   d12p  d12 0    .01
1   d13p -d13 0   d13p  d13 0    .01
1 source
Wire 7, center
1 load
c = 7.631465		; series feedpoint capacitor
Wire 7, center c pF

Sensitivity Analysis

The following table shows the largest performance degradation over 87.5, 93, 98, 103, and 108 MHz in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
     h   0.0010   0.00   0.04
    rp   0.0010   0.00   0.03
   dep   0.0010   0.01   0.11
   d1p   0.0010   0.01   0.10
   d2p   0.0010   0.00   0.11
   d3p   0.0010   0.01   0.07
   d4p   0.0010   0.00   0.10
   d5p   0.0010   0.00   0.03
   d6p   0.0010   0.00   0.11
   d7p   0.0010   0.00   0.09
   d8p   0.0010   0.00   0.04
   d9p   0.0010   0.00   0.07
  d10p   0.0010   0.00   0.13
  d11p   0.0010   0.00   0.10
  d12p   0.0010   0.00   0.04
  d13p   0.0010   0.00   0.03
    ro   0.0005   0.00   0.10
    ri   0.0005   0.00   0.08
    de   0.0005   0.00   0.00
    d1   0.0005   0.00   0.13
    d2   0.0005   0.04   0.23
    d3   0.0005   0.01   0.23
    d4   0.0005   0.00   0.03
    d5   0.0005   0.01   0.28
    d6   0.0005   0.01   0.21
    d7   0.0005   0.00   0.13
    d8   0.0005   0.01   0.24
    d9   0.0005   0.00   0.15
   d10   0.0005   0.01   0.08
   d11   0.0005   0.00   0.04
   d12   0.0005   0.01   0.25
   d13   0.0005   0.00   0.17
     w   0.0005   0.01   0.00
     s   0.0010   0.01   0.05
     c   0.7631   0.24   0.00

Construction

Measure all dimensions to the 10 mm tubing centerline. The loop must be in the element plane in front of the driven element. Support everything with hydraulic tubing clamps. Connect the 75Ω coax center conductor through the specified capacitance to one tube at the feedpoint gap. Connect the shield to the other tube. Make the connections as close as possible to the gap, which should be 2 to 6 mm long. Keep all leads as short as possible. Waterproof the capacitor and connections. Use a 5% ceramic capacitor with the highest voltage rating readily available to minimize the chance of failure due to a nearby lightning strike. Use a current choke at the feedpoint.

Paul Ormandy, ZL4TT, built this loop. For proper coupling to the adjacent director, the connections should be closer to the tubing ends at the feedpoint gap. Nevertheless, Paul reports that the antenna works very well.

Larry Horlick, VO1FOG, built this loop. The short capacitor leads minimize stray inductance.

Dave Kibler, NR8TV, built this neat copper loop with covered feedpoint. Copper/aluminum junctions should be weatherproofed to avoid corrosion due to dissimilar electrode potential that can cause high contact resistance.

It may be easier to construct the driven element and loop with 15 mm × 3 mm flat bars interconnected by 10 mm round tubes with a long bolt or threaded rod inside. The bars are electrically equivalent to 10 mm round tubes.

You can use 6063-T5 aluminum angle from Home Depot. The 0.5″ × 0.5″ right-angle shape is electrically equivalent to a 0.4″ round conductor, which is very close 10 mm. For accurate conductor spacing, mount all elements with the angle oriented the same way. For symmetry, mount the loop sides with the horizontal part toward the boom. The electrical centerline is 0.125″ in from the vertical part.

Check the antenna with a vector network analyzer. Do not alter element lengths or spacings to improve SWR. If you weatherproof it, you can substitute a small air trimmer for the fixed capacitor.

Performance Comparison

Gallery

Dave Kibler erected this six-meter Yagi above a barn in Greenfield, Ohio. He uses a Kitz mast-mount preamp.

Paul Ormandy erected this three-meter Yagi in Oamaru, New Zealand.

Bryan Clark uses this three-meter Yagi in Mangawhai, Northland, New Zealand. The lower Yagi is too close.

Larry Horlick built this three-meter Yagi in Coley's Point South, Newfoundland, Canada.

Larry received these signals over a 24-hour period in July, 2022.


December 23, 2022
88–108 MHz