The Triax FM 8S is an eight-element Yagi for the FM broadcast band made in Europe. It has two reflectors and a 2.31 m (91″) boom.
I modeled the antenna with the AO 9.50 Antenna Optimizer program. The red dot marks the 300Ω feedpoint. The very close spacing of the first director raises the feedpoint impedance.
Marko Weck uses this dual-polarization setup in Kangasala, Finland.
Calculated performance is for 30 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 94.3+j26.2 3.21 1.40 0.02 5.33 9.80
89 122+j59 2.57 0.93 0.01 5.91 11.70
90 156+j87 2.14 0.61 0.01 6.29 13.57
91 193+j107 1.85 0.41 0.01 6.55 15.43
92 234+j118 1.66 0.27 0.01 6.73 17.31
93 273+j119 1.53 0.19 0.01 6.86 19.33
94 308+j110 1.43 0.14 0.01 6.98 21.51
95 336+j95 1.38 0.11 0.01 7.09 24.10
96 356+j79 1.34 0.09 0.01 7.20 23.78
97 371+j64 1.33 0.09 0.01 7.32 23.67
98 384+j50 1.33 0.09 0.01 7.45 23.80
99 398+j35 1.35 0.10 0.01 7.58 24.11
100 416+j15 1.39 0.12 0.01 7.71 24.67
101 435-j22 1.46 0.15 0.02 7.82 21.65
102 439-j82 1.55 0.21 0.02 7.92 19.11
103 397-j157 1.70 0.30 0.02 7.96 17.10
104 305-j201 1.92 0.46 0.03 7.90 15.49
105 201-j187 2.31 0.74 0.04 7.66 14.17
106 125-j132 2.93 1.20 0.06 7.18 13.30
107 80.3-j65.8 3.93 1.89 0.08 6.37 12.86
108 54.2-j3.2 5.54 2.86 0.11 5.14 12.87
Triax FM-8S Free Space Symmetric 98 MHz 18 6063-T832 wires, meters 1 0 -0.835 0.34 0 0.835 0.34 .01 1 0 -0.835 -.34 0 0.835 -.34 .01 1 0.38 -.7225 -.03 0.38 .7225 -.03 .01 1 0.38 .27 .03 0.38 .7225 .03 .01 1 0.38 -.7425 -.01 0.38 -.7425 .01 .01 1 0.38 .7425 -.01 0.38 .7425 .01 .01 1 0.38 -.7425 -.01 0.38 -.7225 -.03 .01 1 0.38 -.7425 .01 0.38 -.7225 .03 .01 1 0.38 .7425 -.01 0.38 .7225 -.03 .01 1 0.38 .7425 .01 0.38 .7225 .03 .01 1 0.38 -.7225 .03 0.38 -.27 .03 .01 1 0.38 -.27 .03 0.38 0 -.015 .01 1 0.38 .27 .03 0.38 0 -.015 .01 1 0.45 -0.6575 0 0.45 0.6575 0 .01 1 0.90 -0.6425 0 0.90 0.6425 0 .01 1 1.315 -.618 0 1.315 .618 0 .01 1 1.77 -.618 0 1.77 .618 0 .01 1 2.305 -.596 0 2.305 .596 0 .01 1 source Wire 3, center Mounting brackets not modeled.
88–108 MHz