FM Cycloid Dipole Omni Antenna with Circular Polarization analyzed using 4nec2. For more info re Cycloid, see: http://www.wa7x.com/cycloid_info.html
Although Raw Gain Vertical, Horizontal and TOTAL (Vertical + Horizontal) Polarization was fairly constant across all angles and frequencies, the Impedance varied considerably. It was 9.2+127j ohms at 87 MHz, rising to 37+410j ohms at 108 MHz, making it very difficult to design a wide-band matching network. Best SWR was about 30:1 with 186-ohm load. Although Analog FM is tolerant of high SWR, Digital FM may not be.
Suppression of Left Hand Circular Polarization (LHCP) is very good across entire FM Band.
Intended for broadcast applications, this (and similar) antennas can be matched to 50-ohms (or 300-ohms) for a NARROW RANGE OF FREQUENCIES by using a matching network (hit "F10" key, L/Pi/T Matching in 4nec2). Matched SWR Chart (at bottom) was the SAME, with ANY of the L, Pi or T Filters - Low or High Pass.
29 Dec 201123 items10315 visitsAlbum by holl_ands
enlarge 42KB, 942x1024 1 FM Cycloid Dipole - Circular Polarized 3D View
enlarge 207KB, 814x1024 2 FM Cycloid Dipole - Circular Polarized Front View [1 small box = 2.5-inches]
enlarge 173KB, 752x1024 3 FM Cycloid Dipole - Circular Polarized Top View [1 small box = 2.5-inches]
enlarge 143KB, 1152x584 4 FM Cycloid Dipole - Circular Polarized FM TOTAL Raw Gain FORWARD (90-deg)
enlarge 155KB, 1152x584 5 FM Cycloid Dipole - Circular Polarized FM TOTAL Raw Gain on DIAGONAL (275-deg)
enlarge 161KB, 1152x584 6 FM Cycloid Dipole - Circular Polarized FM SWR (186-ohms Optimum) is Excessive 30:1
enlarge 187KB, 1152x584 7 FM Cycloid Dipole - Circular Polarized FM SWR (300-ohms) is Excessive
enlarge 167KB, 1152x584 8 FM Cycloid Dipole - Circular Polarized FM SWR (75-ohms) is Excessive
enlarge 156KB, 599x1024 9 FM Cycloid Dipole - Circular Polarized Front View [1 small box = 2.5-inches]
enlarge 326KB, 1024x1024 10 FM Cycloid Dipole - Circular Polarized Azimuthal Patterns at 87 MHz
enlarge 323KB, 1024x1024 11 FM Cycloid Dipole - Circular Polarized Azimuthal Patterns at 92 MHz
enlarge 321KB, 1024x1024 12 FM Cycloid Dipole - Circular Polarized Azimuthal Patterns at 97 MHz
enlarge 320KB, 1024x1024 13 FM Cycloid Dipole - Circular Polarized Azimuthal Patterns at 103 MHz Cir. Pol. beginning to degrade.
enlarge 324KB, 1024x1024 14 FM Cycloid Dipole - Circular Polarized Azimuthal Patterns at 108 MHz Cir. Pol. is degraded.
enlarge 216KB, 1024x927 22 FM Cycloid Dipole - Circular Polarized Must run 4nec2 file before select "F10". Make "RLC Matching (F10)" entries then click on "Use Network". "Z-Load" comes from Impedance Chart at 98 MHz.
enlarge 197KB, 1152x584 23 FM Cycloid Dipole - Circular Polarized FM SWR (300-ohms) is Very Narrowband When using Matching Network. Results are SAME, with L, Pi or T Filters - Low or High Pass.
