Triax FM 8S
The Triax FM 8S is an eight-element Yagi for the FM broadcast band made in Europe. It has two reflectors and a 2.3-meter (91") boom.
I modeled the antenna with the AO-Pro 7.03 Antenna Optimizer program. This image shows the segmentation detail. Blue dots indicate analysis-segment boundaries. The red dot indicates the feedpoint. I did not model the mounting brackets.
Modeling Results
Below are calculated performance figures for a segmentation density of 30 segments per halfwave. Mismatch loss is due to SWR. Wire loss is due to conductor resistance. Mismatched gain is forward gain including wire and mismatch losses. F/B is the ratio of forward power to that directly to the rear. The SWR reference impedance is 300 ohms.
88.000 MHz: Impedance 95.5 + j27.7 ohms
SWR 3.17
Mismatch Loss 1.37 dB
Wire Loss 0.02 dB
Mismatched Gain 5.36 dBd
F/B 9.88 dB
90.000 MHz: Impedance 158 + j88 ohms
SWR 2.12
Mismatch Loss 0.60 dB
Wire Loss 0.01 dB
Mismatched Gain 6.31 dBd
F/B 13.65 dB
92.000 MHz: Impedance 236 + j117 ohms
SWR 1.64
Mismatch Loss 0.26 dB
Wire Loss 0.01 dB
Mismatched Gain 6.73 dBd
F/B 17.37 dB
94.000 MHz: Impedance 310 + j109 ohms
SWR 1.43
Mismatch Loss 0.14 dB
Wire Loss 0.01 dB
Mismatched Gain 6.98 dBd
F/B 21.51 dB
96.000 MHz: Impedance 357 + j79 ohms
SWR 1.35
Mismatch Loss 0.10 dB
Wire Loss 0.01 dB
Mismatched Gain 7.20 dBd
F/B 27.64 dB
98.000 MHz: Impedance 386 + j49 ohms
SWR 1.33
Mismatch Loss 0.09 dB
Wire Loss 0.01 dB
Mismatched Gain 7.44 dBd
F/B 37.60 dB
100.000 MHz: Impedance 418 + j12 ohms
SWR 1.39
Mismatch Loss 0.12 dB
Wire Loss 0.01 dB
Mismatched Gain 7.69 dBd
F/B 25.18 dB
102.000 MHz: Impedance 439 - j82 ohms
SWR 1.56
Mismatch Loss 0.21 dB
Wire Loss 0.02 dB
Mismatched Gain 7.90 dBd
F/B 19.18 dB
104.000 MHz: Impedance 312 - j203 ohms
SWR 1.92
Mismatch Loss 0.46 dB
Wire Loss 0.03 dB
Mismatched Gain 7.89 dBd
F/B 15.53 dB
106.000 MHz: Impedance 131 - j138 ohms
SWR 2.86
Mismatch Loss 1.15 dB
Wire Loss 0.06 dB
Mismatched Gain 7.23 dBd
F/B 13.39 dB
108.000 MHz: Impedance 56.6 - j9.4 ohms
SWR 5.30
Mismatch Loss 2.73 dB
Wire Loss 0.11 dB
Mismatched Gain 5.30 dBd
F/B 12.87 dB
Patterns
Antenna File
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
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Updated July 8, 2007
