If you have a favorite FM station you'd like to better receive and there's no interference from the rear to contend with, consider a dedicated, gain-optimized Yagi. This six-element design has a boom length of 182″ to 226″ depending on frequency.
This shows the antenna geometry. The red dot marks the 75Ω feedpoint.
I optimized for maximum forward gain at 97.5 MHz, the geometric center of the FM band. To slightly broadband the response and reduce sensitivity to modeling and construction errors, I optimized over 97.1, 97.5, and 97.9 MHz. This reduced forward gain 0.23 dB at 97.5 MHz. This is still a narrowband design with no margin for the effects of rain. Gain may drop when the antenna gets wet and response shifts lower in frequency.
The following results are for 34 analysis segments per conductor halfwave with AO 9.64. 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 97.1 43.3+j1.3 1.73 0.32 0.05 10.74 18.89 97.2 47.5+j3.4 1.58 0.23 0.05 10.91 19.12 97.3 52.9+j5.6 1.43 0.14 0.06 11.07 19.38 97.4 59.6+j7.5 1.29 0.07 0.06 11.20 19.23 97.5 68.2+j8.8 1.17 0.03 0.06 11.30 17.48 97.6 79.1+j8.7 1.13 0.02 0.07 11.36 15.95 97.7 92.6+j5.9 1.25 0.05 0.07 11.35 14.60 97.8 108-j2 1.44 0.15 0.07 11.28 13.38 97.9 124-j17 1.70 0.30 0.08 11.12 12.27
Use the frequency scaler to obtain dimensions in inches or millimeters for any frequency between 87.5 and 108 MHz. Dimensions are valid only for isolated ⅜″ or 10 mm 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 the capacitor across the feedpoint, and feed with 75Ω coax. The 5% capacitor should have the highest voltage rating available to minimize the chance of failure due to a nearby lightning strike. Coil the feedline into a current choke at the feedpoint. Read these notes before building anything.
Max-Gain Narrowband Yagi Free Space Symmetric 97.1 97.5 97.9 MHz 6 6063-T832 wires, inches x1 = 0 ; element positions x2 = 29.65504 x3 = 62.6821 x4 = 111.2026 x5 = 159.681 x6 = 202.0254 y1 = 29.0955 ; element half-lengths y2 = 28.57604 y3 = 26.81602 y4 = 26.17355 y5 = 26.05091 y6 = 26.40563 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 source c = 37.26171 ; shunt matching capacitance Wire 2, center c pF
The following table shows the largest performance degradation at 97.5 MHz in dB when altering a symbol value by Tol.
Symbol Tol Gain F/R
x1 0.0394 0.00 0.03
x2 0.0394 0.00 0.02
x3 0.0394 0.00 0.04
x4 0.0394 0.00 0.02
x5 0.0394 0.00 0.03
x6 0.0394 0.00 0.08
y1 0.0197 0.00 0.13
y2 0.0197 0.02 0.00
y3 0.0197 0.03 0.16
y4 0.0197 0.01 0.31
y5 0.0197 0.01 0.31
y6 0.0197 0.00 0.09
c 1.8631 0.03 0.00
Hossein Khamooshi in Gorgan, Iran, scaled the design to 103 MHz and built this vertically polarized antenna for long-distance reception across the Caspian Sea.
Hossein built another antenna for 106 MHz.
Markku Sollo in Tohmajärvi, Finland, built this 93-MHz Yagi for double-hop Es reception from the Middle East.
88–108 MHz