It's difficult to make a Yagi work well over the entire 88–108 MHz band. Multiple driven elements or multiple reflectors are necessary for really good performance. But if bandwidth is restricted, a simple design with excellent performance is possible. I optimized this ten-element Yagi for 88–92 MHz with the AO 9.63 Antenna Optimizer. The boom length is 239″. The red dot marks the 75Ω feedpoint.
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 88.0 56.8-j1.0 1.32 0.08 0.05 10.34 34.54 88.5 64.0+j1.1 1.17 0.03 0.05 10.55 34.85 89.0 73.1+j2.0 1.04 0.00 0.06 10.72 35.35 89.5 82.9+j1.1 1.11 0.01 0.06 10.83 36.06 90.0 92.5-j2.6 1.24 0.05 0.07 10.89 36.47 90.5 99.8-j7.9 1.35 0.10 0.09 10.90 35.93 91.0 105-j13 1.44 0.14 0.11 10.84 34.97 91.5 104-j16 1.45 0.15 0.14 10.76 37.27 92.0 80.3+j8.5 1.14 0.02 0.24 10.67 36.82
Use ⅜″ tubing. Dimensions are valid only for isolated elements (nonconductive boom or insulated mounts). The matching network is the lowpass equivalent of a hairpin match. Split the driven element leaving a gap no larger than ¼″, solder a 27 pF 5% capacitor across the feedpoint, and feed with 75Ω coax. The capacitor should have the highest voltage rating available to minimize the chance of failure due to a nearby lightning strike. Use a current choke at the feedpoint. Read these notes before building anything.
High-Performance Yagi for 88-92 MHz Free Space 88 88.5 89 89.5 90 90.5 91 91.5 92 MHz 10 6061-T6 wires, inches x1 = 0 ; element positions x2 = 21.11459 x3 = 24.88291 x4 = 31.17103 x5 = 41.9917 x6 = 72.39083 x7 = 112.0712 x8 = 154.2972 x9 = 198.2206 x10 = 238.5 y1 = 33.80075 ; element half-lengths y2 = 34.85089 y3 = 31.29524 y4 = 30.21306 y5 = 29.70498 y6 = 29.17727 y7 = 28.86884 y8 = 28.35921 y9 = 28.01402 y10 = 25.71585 1 x1 -y1 0 x1 y1 0 0.375 1 x2 -y2 0 x2 y2 0 0.375 1 x3 -y3 0 x3 y3 0 0.375 1 x4 -y4 0 x4 y4 0 0.375 1 x5 -y5 0 x5 y5 0 0.375 1 x6 -y6 0 x6 y6 0 0.375 1 x7 -y7 0 x7 y7 0 0.375 1 x8 -y8 0 x8 y8 0 0.375 1 x9 -y9 0 x9 y9 0 0.375 1 x10 -y10 0 x10 y10 0 0.375 1 source c = 27.03467 ; shunt matching capacitance Wire 2, center c pF
The following table shows the largest performance degradation over the antenna file frequencies in dB when altering a symbol value by Tol.
Symbol Tol Gain F/R
x1 0.0394 0.00 0.02
x2 0.0394 0.02 0.32
x3 0.0394 0.03 0.41
x4 0.0394 0.01 0.21
x5 0.0394 0.00 0.15
x6 0.0394 0.00 0.24
x7 0.0394 0.00 0.35
x8 0.0394 0.00 0.32
x9 0.0394 0.00 0.33
x10 0.0394 0.00 0.18
y1 0.0197 0.00 0.09
y2 0.0197 0.01 0.09
y3 0.0197 0.04 0.99
y4 0.0197 0.01 0.33
y5 0.0197 0.02 0.73
y6 0.0197 0.01 1.73
y7 0.0197 0.02 1.72
y8 0.0197 0.01 1.14
y9 0.0197 0.01 0.76
y10 0.0197 0.00 0.34
c 1.3517 0.02 0.00
This design uses seven elements on a 119″ boom.
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 88.0 42.2+j0.3 1.78 0.35 0.05 8.18 29.22 88.5 48.2+j2.5 1.56 0.21 0.06 8.42 29.96 89.0 56.4+j3.7 1.34 0.09 0.07 8.63 30.86 89.5 65.9+j3.4 1.15 0.02 0.07 8.76 31.21 90.0 76.7+j0.8 1.02 0.00 0.08 8.81 30.18 90.5 89.1-j4.4 1.20 0.04 0.10 8.75 29.22 91.0 103-j13 1.42 0.13 0.12 8.57 29.23 91.5 110-j27 1.62 0.25 0.16 8.28 29.24 92.0 106+j6 1.43 0.14 0.28 8.09 29.22
Use the same construction as for the larger Yagi. The matching capacitance is 36 pF 5%.
Shorter Yagi for 88-92 MHz Free Space Symmetric 88 88.5 89 89.5 90 90.5 91 91.5 92 MHz 7 6061-T6 wires, inches x1 = 0 x2 = 7.072542 x3 = 12.136979 x4 = 24.279008 x5 = 51.962416 x6 = 83.73561 x7 = 118.5 y1 = 34.113223 y2 = 33.82153 y3 = 31.187681 y4 = 30.339674 y5 = 29.509943 y6 = 29.103275 y7 = 26.58679 1 x1 -y1 0 x1 y1 0 0.375 1 x2 -y2 0 x2 y2 0 0.375 1 x3 -y3 0 x3 y3 0 0.375 1 x4 -y4 0 x4 y4 0 0.375 1 x5 -y5 0 x5 y5 0 0.375 1 x6 -y6 0 x6 y6 0 0.375 1 x7 -y7 0 x7 y7 0 0.375 1 source c = 36.79368 Wire 2, center c pF
The following table shows the largest performance degradation over the antenna file frequencies in dB when altering a symbol value by Tol.
Symbol Tol Gain F/R
x1 0.0394 0.00 0.02
x2 0.0394 0.02 0.17
x3 0.0394 0.03 0.26
x4 0.0394 0.01 0.16
x5 0.0394 0.00 0.16
x6 0.0394 0.00 0.20
x7 0.0394 0.00 0.10
y1 0.0197 0.00 0.10
y2 0.0197 0.02 0.08
y3 0.0197 0.09 0.59
y4 0.0197 0.04 0.75
y5 0.0197 0.03 1.14
y6 0.0197 0.02 0.53
y7 0.0197 0.01 0.16
c 1.8397 0.05 0.00
Two of the three ten-footers Jakub Melin erected for rebroadcast reception of Radio Hey in the Czech Republic.
Joe Hageli built an earlier version of the ten-footer in Spring Grove, Illinois.
Performance for these designs degrades rapidly above 92 MHz. When the antenna is wet, performance may degrade for frequencies somewhat below 92 MHz as the response shifts to the left.
88–108 MHz