Antennacraft FMSS FM Turnstile (two Folded Dipoles at 90-degrees to each other) analyzed using 4nec2. [Similar to Wade CFM-FM, Wade OFM-1 and Winegard HD-6010, except non-Folded is 75-ohm output.]
Per FMSS Specs, Folded Dipole Elements = 55-in long with overall structure Height = 8-in. Separation between Elements appears to be about 2-in, leaving about 4-in between the Crossed FD's. Per FMSS Manual, Feedline is 9-in long and appears to be 450-ohms open ladder twinlead, although modeling with 300-ohm twinlead revealed minimal differences, assuming it was the same ELECTRICAL length (shorten by velocity factor).
Antenna Pattern maximums are on two diagonals, 300-deg for High Freqs and 335-deg for Low Freqs. There are significant Gain Holes on the opposite Diagonals (40-60 & 220-240 degrees).
Across all angles and frequencies, Raw Gain ranges from -14 to +1.3 dB (Horizontally Polarized). SWR (300-ohms) was 2.9, dropping to 1.5 at high frequencies.
FYI: FMSS Folded Dipole lengths are not quite optimum for Min SWR. Longer, 62.5-in FD Elements minimized SWR, which was under 1.9, but decreased Raw Gain by a few tenths of a dB.
Date(s): 22 Dec 2011. Album by holl_ands. 1 - 17 of 17 Total. 6388 Visits.
enlarge 57KB, 1024x663 1 FM Turnstile - Antennacraft FMSS 3D View
Study this diagram very carefully to determine diagonal direction for Max Gain.
enlarge 90KB, 1152x278 2 FM Turnstile - Antennacraft FMSS "Front" View [1 big box = 5-inches]
enlarge 252KB, 1024x973 3 FM Turnstile - Antennacraft FMSS Top View [1 big box = 5-inches]
enlarge 141KB, 1152x584 4 FM Turnstile - Antennacraft FMSS FM Raw Gain FORWARD (90-deg) Gain Loss on Low Frequencies
enlarge 142KB, 1152x584 5 FM Turnstile - Antennacraft FMSS FM Raw Gain on DIAGONAL (45-deg) Large Gain Loss on ALL Frequencies
enlarge 137KB, 1152x584 6 FM Turnstile - Antennacraft FMSS FM Raw Gain to SIDE (0-deg) Gain Loss on High Frequencies
enlarge 156KB, 1152x584 7 FM Turnstile - Antennacraft FMSS FM Raw Gain on DIAGONAL (300-deg) Gain Loss on Low Frequencies
enlarge 157KB, 1152x584 8 FM Turnstile - Antennacraft FMSS FM Raw Gain on DIAGONAL (335-deg) Gain Loss on High Frequencies
enlarge 192KB, 1152x584 9 FM Turnstile - Antennacraft FMSS FM SWR (300-ohms) Under 2.9
enlarge 149KB, 1152x584 10 FM Turnstile - Antennacraft FMSS FM Impedance
I'm not even a hobbyist of antennas. Just want really good reception. I found this site trying to figure out if the AntennaCraft FMSS omni can be mistakenly placed upside down, or should it be, or should it be placed vertically so the x axis is pointing toward the stations I like (college,PBS, 88 - 92Mhz). I know it's advertised as omni-dir. Does that mean spherically? or 360* on the horizontal plane? The diagrams are all based on the antenna in the horizontal position (z axis vertical). So I set mine that way and it does work fairly well, but not excellent. Can anyone help point me in the right direction? :) please! - edward, Sun, 25 Aug 2013 10:22AM