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It appears that your questions regarding optimal mounting height for your Sigma 5 have been very well addressed by the reflector members. I just want to reply to the question in your initial message about the effect of a hillside on an antenna's radiation pattern. The answer is a resounding "Yes!" - it can make a huge difference. Theoretically, if your antenna were mounted on a continuous downward slope of, say, ten degrees, and the slope extended throughout the fresnel zone for a given frequency, you would simply subtract ten degrees from the takeoff angle you'd have over flat terrain. In practice this is seldom the case, as sloping terrain is usually irregular, and the takeoff angles are formed by a complex interaction of reflection and diffraction. About the only way to look at this is by computer simulation, and I like Brian Beezley's (K6STI) old DOS-based TA program. From my own experience, the plots shouldn't be taken too literally, but they seem to give an excellent approximation. Note that it plots only for a horizontally polarized wave, but I've found that the actual performance of verticals seems to be similar. For quite some time now, I have had a second QTH in an old trailer on a steep hilltop rising about 350' over average terrain (photo on QRZ.com). I don't get to use it as much as I'd like, but it definitely works; when I first started using it, it almost literally seemed magical. With 300 watts and a modest 20m yagi at 63', I was easily working low-power central Asian stations that almost no one else could even hear. Years later, when the TA software came out, I saw quantitatively what was happening. On the plots, sharp low-angle lobes in many directions were as much as 20 db over the same-angle lobe formed on flat terrain. For long-haul dx, this very modest hilltop station usually holds its own even against the really incredible superstations that have appeared in recent years. However, it does not have the versatility/adaptability of stations with multiple switched stacked yagis on 200' towers, and will often lose out when propagation favors the higher angles. And, of course, the brute force of four stacked six-element yagis over flat terrain, fed with a 3 kw amplifier, is simply very effective. But I get a lot more decibels per dollar! 73, Al K8AL -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force12 Web Site: http://www.force12inc.com To Submit Message to the List: Force12Talk@qth.com To unsubscribe and view the Message Archive: see http://qth.com/force12/list For problems with the list: contact n4zr@qth.com |