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It is a truism
On Friday, November 14, 2014 11:46:03 AM UTC-6,
Generally for DX a takeoff angle of 30 degrees or less is the rule of thumb for best general performance. Of course the antenna still "works" at other heights, but if DX is what you want to achieve, then best results, on the average over average ground, the antenna will work best for that at a height of .5 lambda or better. Yep, for 80m, it's usually easier to put up a good vertical for dx than a high dipole. And even then sometimes the vertical will do the best. W8JI talks a lot about this comparing his 160m verticals and his high 160m dipoles. Most times, his verticals still win to long paths. I forgot how high his dipole was, but it's pretty high vs what most people have. People talk about short antennas being poor radiators, but on 40m with my appx 40 ft tall full size dipole fed with coax, my mobile antenna would beat it most every night from Houston to Jacksonville FL. I thought maybe it was a fluke, but I tested it a few more times, and it almost always won. So the most efficient antenna does not always win the race if the less efficient antenna puts more rf at the lower angles where you want for longer paths, vs the highly efficient antenna like my coax fed dipoles. At 40 ft on 40m, it's still shooting a lot of rf at fairly high angles, and not so much at the low angles. Less than my mobile antenna did. I remember one night I was at the coast fishing, and I actually ran a wide braid ground wire from the truck body into the ocean just to add that extra gusto. On longer paths, I was smoking some people using dipoles and running amps vs my extended 14 ft tall mobile antenna sitting on the beach with 100w. So much for small antennas always being poor radiators.. :/ Efficiency isn't always everything. But it usually is for NVIS paths, which is why I've always preferred coax fed dipoles for my usual 75m NVIS chatter. |