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Jerry Martes wrote:
"I`d like to get some "real life" data." End effect on dipoles and monopoles has little do with comparitive performance. See Cebik. It`s more associated with where the antenna is with respect to ground, and how fat or slim the conductors are. Jerry also wrote: "I want to understand (see) what kind of pattern I`m getting from an antenna I made for Weather Satellite (137 MHz) reception." That might be for the NOAA polar orbiters. On page 19-8 of the 19th edition of the ARRL "Antenna Book" is a section on Antennas for Satellite Work. Circular polarization is considered ideal. A couple of NOAA polar orbiting satellites are active and others may be functioning as backups. Active NOAA orbiters may fly high over the horizon a couple of times a day, so you need a program to tell you where, when, and how high above the horizon the flyover will occur. Some are available at no cost, I hear. 15 minutes of visibility, 7 minutes coming and 7 minutes of going may be available on a pass. On page 19-10 of the "Antenna Book" are shown the patterns of individual dipoles and as used together as an omnidirectional turnstile. The quadrifilar helix is also considered good as a weather satellite receiving antenna. This antenna is shown on page 292 of J.D. Kraus` third edition of "Antennas for All Applications" in Figure 8-67. No need for concern about the pattern obtained from folded dipoles if you are OK with the pattern of an ordinary open-circuit dipole. They are exactly the same. The difference is only in the inherent impedance transformation of the folded antenna, dipole or monopole. That`s it. Antenna catalogs list gain as 0 dBd for open-circuit dipole, folded dipole, ground plane, or folded monopole. Patterns shown are the same for open-circuit and folded dipoles. Patterns shown for a folded monopole are identical with those shown for an open-circuit monpole (ground plane). One catalog lists a thin-wire common dipole as having 34% bandwidth and a 60-ohm feed resistance. The folded dipole has a 45% bandwidth and a 300-ohm feedpoint because it is fatter and folded. The pattern plots are identical. Enjoy your EZNEC. The resuts it should prduce on ordinary and folded dipoles are already published in many places. Makes it easy to see if you did the EZNEC right. Best regards, Richard Harrison, KB5WZI |
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