Nice report Scott! Where you are on the mountain can create some astonishing results;
1) If you were somewhere on the side - below the peak - you probably had significant low-angle "gain" away from the mountain. At the height above the ground you had your antennas, the ground nearby acted like a reflector in a beam. In this case the main lobe is not straight up, as in a NVIS antenna on level earth, but since were on a slope it was skewed down toward the horizon where it's better for working longer distances. Of course the signal is much, much stronger *away* from the mountain than through it ;-) Some dedicated mountain enthusiasts even arrange "inverted V" dipoles held by a single support sticking out sideways on a cliff face to enhance this effect, but it's very real even on more reasonable slopes. 2) If you were on the very peak of the mountain, the mountain itself acted like an antenna support. For the ground to act like normal level ground, it needs to extend several wavelengths away from the antenna. At our home QTHs on nearly level ground, that's a limitation. On a mountain peak, that's a real advantage! Objects many wavelengths away (like those other mountains in the vicinity) aren't likely to cause any noticeable effect. That's where Marconi and the experts of his time disagreed. Hertz had shown that a simple piece of metal would stop electromagnetic waves. What people (including Hertz) didn't realize at the time was that Hertz' waves were in the VHF range, from what later engineers could determine. They are stopped by a significant piece of metal. Marconi, after hearing his spark signals over a small hill on his family's estate, was convinced that Hertz was wrong. Marconi was right, since he was using very low frequency signals in the range of a few hundred kilohertz. I've seen the effect described in a way one can visualize as putting a breakwater - a stone wall jutting above the waves - in a harbor entrance. A small breakwater will stop the turbulent rapid (high frequency) water movement, but longer, slower (lower frequency) waves will "wrap" right around it and show up on the other side. The bigger the breakwater, the longer wave (lower frequency) wave it takes to pass around it: shorter (higher frequency) waves are more effectively blocked. Understanding that, and not realizing there were other propagation mechanisms, such as refraction of radio waves by the ionosphere and even the surface of the earth itself, is what led early engineers to believe that lower frequencies - longer waves - were essential for long distance communications. It was that misunderstanding that put us Hams on "200 meters and down". We were given the "short waves" in the mistaken belief that they had no commercial value and no one, including us Hams, would "be able to get out of our back yards" on such short wavelengths. Of course, as soon as we Hams discovered how effective ionospheric propagation was for long range short-wave communications, just as you did working stations on the far side of those nearby mountains, they took most of those "useless" short wave frequencies back :-) Ron AC7AC -----Original Message----- Subject: [Elecraft] dipole antenna & camping trip Here is some antenna information that might supprise you! I was planning a camping trip to the mountains and needed a dipole antenna for my K2/10. I would be camped in a heavly wooded area and space between trees would be small. So before leaving home I built a 20 meter dipole because it would be short and would be easier to get in between the trees. Then I decided it would be nice to have 40 meters if I had the room, so I took two end clamps off of a battery jumper cable and clamped them to the end of the 20 meter dipole, then added enough wire to the clamps to make it a 40 meter dipole. When I installed the antenna at 8000 feet alt I had enough room for the 40 meter addition. The center was 25 feet off the ground, one end was 20 feet up and the other 6 feet off the ground. I found that with the 40 meter attachment with the battery cable clamps the antenna was resonate on 40, 20, and 15 meters with an swr of .1 on all three bands. Even in the heavly forrested area I worked stations all over the US and Canada. Just to the north of me was a mountain range that went above the timberline, but I didn't seem to have any trouble getting over it, and to the south was another that was about ten thousand feet high. They didn't seem to effect my signals. I was running 10 watts the whole time. The bears even left me alone! 73 Scott N5SM _______________________________________________ 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
