Mike KK5F wrote: For an HF dipole installed along a stony cliff or bluff, I've always had my doubts that the earth and stone behind the dipole act much like an effective ground reflector. If the height above average terrain of this cliff dipole is, say, 1000 feet, I suspect that the antenna actually functions mostly as if it were just a dipole that is well elevated above average terrain level ground. But I may be wrong. I've had good results when I've been in a position to use a near-cliff dipole, but I never tried to determine if there was any noticable directivity effect.
Similarly, if the same antenna is centered on an elevated narrow ridge, how well will the elevated earth of the ridge actually function as an effective antenna ground, compared to the ground effects of the terrain at the bottom of the ridge? -------------------------------------------------------------------------- Quite right, Mike, assuming the width of the ridge is quite narrow in terms of wavelengths. Although antenna modeling programs claim there's LOTS of gain (about 6 dB max) with the antenna elevated about 0.2 wavelengths even over fairly poor grounds, I try to never confuse a model generated by a computer with the real world until I've actually seen it demonstrated in the real world. Unfortunately, us Hams have precious little resources with which to do real world antenna measurements. I've never "mountain-topped" on the very top ridge of a narrow mountain (say, less than 100 feet or so wide) and, not being a rock-climber, most of the mountains I've operated from had plenty of soil on the slope. Where I chose to set up operations might be a rocky outcropping, but there's always lots of earth around within a couple of wavelengths (few hundred feet on 40 meters, where I most often go portable). My impressions when working from such locations are: 1) When operating from mountains I seem to "get out" much better than with an equivalent antenna on flat land, 2) I can work DX that I can't work with the antenna at the same height on flat land and 3) That I can't work stations worth a darn on the other side of that mountain! As you say, all of those things are pretty obvious, regardless of whatever "gain" any ground reflection provides. Just getting the antenna up on a slope where only a little lossy earth is nearby might account for the same effects. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
