FM + VHF 8-Spokes Vertically Polarized Discone Antenna analyzed using 4nec2. I determined dimensions mostly via trial and error, resulting in barely acceptable (3:1) SWR on the lowest frequency (88 MHz) and reduced Gain (0 dBi) on the highest frequency (216 MHz). Gain=1.4 dBi in FM Band. [Somewhat larger antenna JUST for FM Band adds 0.2-0.3 dBi.]
Presumed use of AWG10 and 60-degree Complimentary Cone Angle measured from the X-Y Plane. [Some references measure Cone Angle to the Z-Axis.] Cone Whisker Length=36-in, Disc Radius=20-in, Feedpoint Gap=2.0-in, Inner Circle Radius=1-in.
Polarization is almost completely Vertical. Elevation Gain charts reveal that Gain in FM Band is directed at Horizon (Elev=0-deg). However, in Hi-VHF Band, Gain is significantly below the Horizon...hence the depicted antenna SHOULD be mounted UPSIDE-DOWN from shown. Ditto for commonly encountered off-the-shelf VHF Discone Antennas.
26 Aug 201219 items6462 visitsAlbum by holl_ands
enlarge 95KB, 861x1024 1 FM + VHF 8-Spoke Discone 3D View
enlarge 220KB, 1024x865 2 FM + VHF 8-Spoke Discone Front View [2 big box = 5-inches]
enlarge 238KB, 996x1024 3 FM + VHF 8-Spoke Discone Top View [2 big box = 5-inches]
enlarge 190KB, 1152x692 4 FM + Hi-VHF 8-Spoke Discone Ch2-13 Raw Gain drops off across Ch7-13
enlarge 213KB, 1152x692 5 FM + Hi-VHF 8-Spoke Discone Ch2-13 SWR (75-ohm) is Good except below FM Band
