• Public Gallery  • Help
		• Join Now!  • Log In  • Feature Tour

holl_ands | Home > Circular Polarized incl. Rabbit-Ears > Helical Circular Polarized > Browse:Hi-VHF Helical - Offset FeedHi-VHF Helical - Center Feed
Hi-VHF Helical - Offset Feed Hi-VHF Helical (Axial-Mode) Circularly Polarized Antennas with Off-Set Feed is analyzed using 4nec2. 1) Hi-VHF: Offset Feed, 185 MHz Design Frequency, 5.5 Turns, C/WL=1.133 (presumably close to optimum), Alpha=arctan(S/C)=14.5-deg (presumably close to optimum), where C=Helix Circumference, WL=Wavelength, Alpha=Helix Spiral Angle and S=Size of One Turn along the X-axis. Calculated parameters: R=29.24-cm (11.5")=Helix Radius, S=47.52-cm (18.7") and L=2.6134-m (102.9")=Helix Length. Characteristic Impedance is optimum (under 1.4) for 200-ohms, but is still quite good at 300-ohms, as plotted below. EDIT (19 Jan 2011): Added Circular Polarization Patterns as an Animated-GIF.....Looks Good.... Date(s): 9 Feb 2001. Album by holl_ands. 1 - 28 of 28 Total. 2086 Visits.
enlarge 128KB, 1024x843 1 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Design Frequency = 185 MHz for Best Gain, F/B & SWR Offset Feed: Half-way down from Center enlarge 163KB, 1152x494 2 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Side View Side View [1 small box = 5-cm] enlarge 297KB, 1024x878 3 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Front View [1 small box = 2.5-cm] enlarge 174KB, 1024x959 4 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: 3D View Feedpoint DETAIL enlarge 164KB, 1152x490 5 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Top View Top View [1 small box = 5-cm] enlarge 41KB, 791x1024 6 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: 4nec2 File enlarge 168KB, 1152x717 7 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Hi-VHF Raw Gain Ch7-13 enlarge 200KB, 1152x717 8 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Hi-VHF SWR (300-ohms) Under 1.9 enlarge 158KB, 1152x717 9 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Hi-VHF Impedance Ch7-13 enlarge 318KB, 1024x1024 10 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Hi-VHF Patterns at 174 MHz enlarge 322KB, 1024x1024 11 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Hi-VHF Patterns at 198 MHz enlarge 325KB, 1024x1024 12 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Hi-VHF Patterns at 216 MHz enlarge 148KB, 1024x792 13 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: 3D Total Gain Pattern at 198 MHz enlarge 142KB, 1024x784 14 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: 3D Horiz Gain Pattern at 198 MHz enlarge 141KB, 1024x789 15 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: 3D Vertical Gain Pattern at 198 MHz enlarge 196KB, 1152x717 16 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Raw Gain FM to 300 MHz enlarge 231KB, 1152x717 17 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: SWR (300-Ohms) FM to 300 MHz enlarge 187KB, 1152x717 18 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Impedance FM to 300 MHz enlarge 310KB, 1024x1024 19 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint Circular Polarization Patterns at 174 MHz enlarge 310KB, 1024x1024 20 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint Circular Polarization Patterns at 180 MHz enlarge 311KB, 1024x1024 21 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint Circular Polarization Patterns at 186 MHz enlarge 314KB, 1024x1024 22 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint Circular Polarization Patterns at 192 MHz enlarge 315KB, 1024x1024 23 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint Circular Polarization Patterns at 198 MHz enlarge 317KB, 1024x1024 24 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint Circular Polarization Patterns at 204 MHz enlarge 316KB, 1024x1024 25 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint Circular Polarization Patterns at 210 MHz enlarge 320KB, 1024x1024 26 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint Circular Polarization Patterns at 216 MHz enlarge 199KB, 1024x1024 27 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feedpoint - Ani-Gif Circular Polarization Patterns enlarge 216KB, 1152x710 28 Hi-VHF 5.5-Turn Helical, C/WL=1.133, Alpha=14.5-deg Offset Feed: Hi-VHF SWR (75-ohms) Under 2.9 Usable although not as low as for 300-ohms. It may be possible to improve matching for 75-ohms.
Select All.
Sign the Guestbook. There are no entries.