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![]() "Jim Lux" wrote in message ... John KD5YI wrote: "JB" wrote in message ... The 1/4 wave ground plane has a useless pattern. Main lobe at about 30 degrees above horizon, but broad enough to be usable and simple to build. The quarter-wave antenna's height above ground has much more to do with the elevation angle than the fact that the antenna is a quarter-wave ground plane. Using EZNEC, I see that a quarter wave antenna situated 3 wavelengths above real/high accuracy ground of medium characteristics has a main lobe 4 degrees above the horizon. At that angle, the gain is 5.1 dBi. You can confirm this if you have a copy of EZNEC. John If you're just looking for a portable vertical antenna, just a wire on the end of the coax, and hanging it up, works pretty well. The shield of the coax (outside surface) serves as the other half of the dipole. Heck, it will have a bizarre pattern, and couple RF everywhere, but you're talking about an antenna you're hanging out of a hotel window or something.. You're not doing earth-venus-earth radar tests... you're just getting the antenna away from where you are sitting to "outside".. If you are using such construction, why not just build a coax type of colinear? It isn't so difficult to add a section of outer shield for decoupling. Have you priced PA hybrids lately? BTW any degree uptilt is usually worthless unless you are deliberately limiting coverage to the horizon. and anything significantly higher in elevation is line of sight anyway. For ground level base station or repeater that covers a localized area, a J-pole is attractive because of its broad pattern that allows numerous reflections through and between the buildings. I've been told that an upside down ground plane ought to work better, but it doesn't |
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