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On Thu, 10 Feb 2005 03:49:58 GMT, Rick Frazier
wrote: I'm thinking I can set the angle of radiation for a horizontal dipole, by hanging it the proper distance above (and or towards or away from the desired direction) to essentially add to the desired angle of radiation, if only by some small amount. Hi Rick, This is true, but probably not for the reasons you may have envisioned. Simply put, the metal acts as a shield to prevent loss to ground. What is not lost is radiated in other directions. It aids in those directions straight up, but it also aids in directions at every other angle too - net result: better signal; how much: nothing dramatic. This simple fact will probably get you more initial gain than you will add doing anything further (short of building a tower and putting up a beam). Is there an optimum angle of radiation for DX, Yes - you may hit it poorly tho'. Though optimizing the location of the dipole for a particular angle of radiation seems good, there will also be a corresponding cancellation of signals at other (calculable) angles of radiation, right? Odds are that given this vague description, that, yes, anything could happen. Guessing your intent, well you are already in illusionland with optimization - unless, of course, 1dB optimizations light up the stars in your firmament. Is it all for naught anyway? Given the action of a wire reflector, will the sheet metal slab only look like a larger version and only in the general direction perpendicular to the center of the sheet metal axis? Practical answer is no one will probably notice even if you could shift everything around to suit your best guess. You have far more dramatic opportunities (more than 1dB) with a vertical within sight of the ocean. 73's Richard Clark, KB7QHC |
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Angle of Radiation - Hawaii
Hello:
I live in Hawaii, the land of metal roofing, and got to thinking on the way home tonight, that instead of complaining about it, I may be able to put the metal roof to some sort of advantage with regard to DX communications. I'm thinking I can set the angle of radiation for a horizontal dipole, by hanging it the proper distance above (and or towards or away from the desired direction) to essentially add to the desired angle of radiation, if only by some small amount. Think of the roof as an rf mirror about 60 feet long and 20 feet wide. Pitch is about 5 inches per foot, so it's a relatively low slope. A wire (source) located perpendicular to and centered on the roof/reflector would be a pretty high angle of radiation. Of course, the distance from the reflector to the dipole would want to be an optimum distance so it reinforces the signal instead of cancels it. One would think that this high angle of radiation should be able to be changed (shifted lower) by moving the dipole away from the desired direction of radiation. Of course, I would expect only a relatively small portion of the signal is actually affected this way, because the reflector is only a relatively small percentage of 180 degrees... Or, maybe not... A wire dipole, with a wire reflector behind it does increase gain in the forward direction, and the wire reflector is only an extremely small portion of the nearly 180 degree arc behind the driven element. OK, now comes the fun part. There are (at least) three questions: Is there an optimum angle of radiation for DX, (lower is better, to a point?) given that I'm 2300+ miles from the nearest land, and may be most interested in locations half way 'round the world and not just the nearest land, (which I can talk to just fine right now, thank you)? Though optimizing the location of the dipole for a particular angle of radiation seems good, there will also be a corresponding cancellation of signals at other (calculable) angles of radiation, right? Is it all for naught anyway? Given the action of a wire reflector, will the sheet metal slab only look like a larger version and only in the general direction perpendicular to the center of the sheet metal axis? I've gone and done it now, got myself questioning more than I thought I knew... How 'bout you? Got any opinions? Thanks -_Rick |
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