If you use an indoor folded dipole to receive broadcast FM, you can increase signal strength a few dB by placing a wire near the antenna. Pick one of the following designs based on the favored direction and mounting constraints. The models included 300Ω mismatch loss during optimization to obtain the maximum forward gain possible without antenna rematching.
Placing a parallel wire a few feet above or below a horizontal folded dipole can improve bidirectional gain as much as 3 dB. The azimuth pattern is unchanged and the elevation pattern maximum is almost exactly at the horizon. The wire only slightly reduces antenna impedance. The lower wire is likely to be too close to ground if the antenna is on the ground floor. But if oriented vertically, the antenna will work well anywhere. Its azimuth pattern will be the elevation pattern shown above.
This shows free-space performance for several designs optimized with AO 9.66. The curves include conductor and mismatch losses. All designs use the folded dipole shown in black. It is resonant near 96 MHz with equal gain at the band edges.
Use these lengths and spacings for bare #14 copper wire:
Length Spacing
Low 62.125″ 85.75″
Mid 58.375 77.625
High 55.125 70.75
Broad 67.375 57.625
When detuned from the length that yields maximum gain regardless of impedance, a reflector can still provide worthwhile broadband gain. Place the wire at the folded dipole height on the side away from the favored direction.
Use these lengths and spacings for bare #14 copper wire:
Length Spacing
Low 63.625″ 25.125″
Mid 57 27.125
High 54 30.25
Broad 63.25 23.75
Place the wire at the folded dipole height on the side toward the favored direction.
Use these lengths and spacings for bare #14 copper wire:
Length Spacing
Low 59″ 25″
Mid 55 19
High 52 11.375
Broad 50.625 30.25
88–108 MHz