Low antennas in high places
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I would like to correspond with anyone who has tried portable QRP
operation from a high location, using a low horizontal antenna at the edge of a sharp dropoff. In the Moxon antenna book (chapter 10), he says that a simple dipole or inverted vee at a low height in such a location can show excellent gain at low angles. I have an great application for this, if it really works! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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I just used a portable inverted vee fed with 300 ohm ladder line and the
elecraft 4:1 balun during our camping trip up in the hills of northwest NJ. The K2 heard like a hawk. I had it up about 30 feet and the ends were maybe 8-10 feet off the ground. 1st QSO I snagged Switzerland on 40 meters running 5 watts. Good sigs. I'd say it was working! Antenna was one of these.. http://cgi.ebay.com/Portable-Antenna-System-QRP-and-QRO_W0QQitemZ5789737741Q QcategoryZ4672QQcmdZViewItem James Kern Network Administrator Kurt S. Adler, Inc. 1107 Broadway New York, NY 10010 212-924-0900 x222 (work) 212-807-0575 (fax) 908-451-6801 (cell) 800-209-7438 (pager) [hidden email] -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Vic K2VCO Sent: Tuesday, August 09, 2005 2:14 PM To: Elecraft Reflector Subject: [Elecraft] Low antennas in high places I would like to correspond with anyone who has tried portable QRP operation from a high location, using a low horizontal antenna at the edge of a sharp dropoff. In the Moxon antenna book (chapter 10), he says that a simple dipole or inverted vee at a low height in such a location can show excellent gain at low angles. I have an great application for this, if it really works! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by Vic K2VCO
Vic,
I have noticed the effect in the San Jacinto Mtns east of here. I was at around 8000'. I layed out my end-fed wire as a sloper with the low end pointing east on relatively flat terrain at the campground. I later moved it so that it sloped from the edge of a drop off down to a scrubby tree on an outcropping, with the far (low) end still east. Subjectively, it heard better...maybe an S-unit. I think I first heard about the idea in an issue of the Adventure Radio Society magazine (www.arsqrp.com). You would have to search through back issues, but I'm pretty sure it's there. If I run across it, I'll send you the URL. Eric KE6US www.ke6us.com -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Vic K2VCO Sent: Tuesday, August 09, 2005 11:14 AM To: Elecraft Reflector Subject: [Elecraft] Low antennas in high places I would like to correspond with anyone who has tried portable QRP operation from a high location, using a low horizontal antenna at the edge of a sharp dropoff. In the Moxon antenna book (chapter 10), he says that a simple dipole or inverted vee at a low height in such a location can show excellent gain at low angles. I have an great application for this, if it really works! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
Re: Low antennas in high places
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In reply to this post by Vic K2VCO
Vic wrote:
>I would like to correspond with anyone who has tried portable QRP >operation from a high location, using a low horizontal antenna at the >edge of a sharp dropoff. I always got great results operating from a bluff on Arkansas' Mount Magazine and similar locations, by running the ends of a dipole to adjacent outcroppings just above local ground level. It even worked well on 80m. Even when well away from a bluff edge, operating a dipole on an elevated plateau or ridge seems to work well. Gotta love a resonant dipole! 73, Mike / KK5F _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by EricJ-2
This past Field Day, we used some NVIS dipoles atop a hill in Austin TX.
There was a sharp drop to the east and to the West. We not only worked obvious NVIS range signals; but worked a number of skip signals from antennas no more than 7 feet high at the highest. The 40m antenna was only 3 1/2 feet high. We think the drop off enhanced the ability of these low antennas. Signals on 75m to the NW coast were 5,6 to 5,7 consistently, but contacts were relatively easy to make. If you heard a station, he could hear you. Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Paul,
NVIS (Near Vertical Incidence Skywave) dipoles or antennas are any antenna operated at low elevations above ground from lying on ground to being say 0.1 wave high, and certainly well below conventional heights for that antenna. They are horizontal dipoles usually a half wave type, or tuned, if shorter. They are used to increase your signal level at a few hundred miles by firing straight up at 80 to 90 degrees with most of your signal, and minimizing pickup of low angle noise. However, they also can have a skip component of signal allowing 5,7 operation on SSB out to West Coast from here in Central TX. In state, they increase a 100 watt signal from S8 to 20 over S9, by lowering the same antenna! Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
RE: Low antennas in high places
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Stuart wrote:
NVIS (Near Vertical Incidence Skywave) dipoles or antennas are any antenna operated at low elevations above ground from lying on ground to being say 0.1 wave high, and certainly well below conventional heights for that antenna. --------------------------- The optimum height is 0.2 wavelength. It's no surprise that's the optimum spacing for a two-element beam. The earth acts as a reflector behind the driven element. If the spacing (height of an NVIS antenna) goes beyond 0.2 wavelength, the pattern starts to spread toward the horizon. That's why we try to get our horizontal dipoles that will be used for DX up above that height! One cravat there is that you don't always know the 'effective' height. Over dry, sandy soil or rocks the effective height may be greater than the height of the radiator above the ground. Lower heights work too, but as the antenna is brought closer to the earth the overall gain drops due to ground losses. At 0.2 wavelengths, the NVIS will show over 6 dB of gain straight up: that's equal to quadrupling your transmitter power! The advantage of low dipoles on slopes for DX noted by Moxon is that the earth behind the radiator acts as a reflector. If you have a vertical cliff, you have a two-element beam pointing in the direction the radiator is facing. Even more gentle slopes will produce good results because that "vertical" lobe is actually very broad. A 20 or 30 degree slope will put a lot of RF out near the horizon. And a BIG advantage to a cliff-side antenna is much reduced ground losses in the far field. Most low angle radiators lose a lot of low-angle radiation because of the ground losses around it (unless you're at sea surrounded by salt water). Even a vertical, which theoretically has maximum gain at zero degrees to the horizon, will show little radiation below 20 or 25 degrees. All that radiation down lower is converted to heat in the earth. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
RE: Low antennas in high places
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In reply to this post by Vic K2VCO
Ron wrote:
>The advantage of low dipoles on slopes for DX noted by Moxon >is that the earth behind the radiator acts as a reflector. 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? 73, Mike / KK5f _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
RE: Low antennas in high places
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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: [hidden email] 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 |
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In reply to this post by Mike Morrow-3
This is all interesting and especially to me because at our club meeting
tonight the program is going to be on NVIS antennas! Rol Anders one of our guys and chief engineer of the corporation that used to be Westinghouse..... can't think of the present name right now.... Anyway he has the program on NVIS antennas and he is writing an article for QST. Paul Gates K1 #0231 KX1 #1186 XG1 [hidden email] ----- Original Message ----- From: "Mike Morrow" <[hidden email]> To: "'elecraft'" <[hidden email]> Sent: Thursday, August 11, 2005 1:19 PM Subject: RE: [Elecraft] Low antennas in high places > Ron wrote: > > >The advantage of low dipoles on slopes for DX noted by Moxon > >is that the earth behind the radiator acts as a reflector. > > 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? > > 73, > Mike / KK5f > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > 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 > Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by Ron D'Eau Claire-2
No matter what the ground conductivity is at a given hill top located
antenna, what is shown in one ARRL Antenna Compendium piece on gains from an antenna near the edge of, and atop a hill, is that you are no longer shadowing say, a dipole parallel to the cliff face from radiating at angles below zero degrees. (Zero being parallel to the horizon, and any angle below horizon being called negative for this discussion.) This signal, which is usually absorbed by nearby earth in the near field for conventional dipoles on flat ground, may have enough space to radiate quite a ways at a low or negative angle, then it might reflect in the Fresnel zone, (far field), or even just a few wavelengths from the hill. In any case, by the laws of wave reflection, angle of incidence equals angle of reflection, and thus the ground reflection will head for the ionosphere at a very favorable for DX, low angle of take off. Thus, the advantage of a horizontal antenna near the cliff edge on top of a hill. Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by Mike Morrow-3
Mike, consider that the soil on some cliff tops is the same as that at the
base, if the cliff is formed as a geologic fault. Then, it would be no better nor worse than the soil down on level ground. That is not the main reflection gain mechanism from the elevated cliff side dipole, as my other post points out. It is the lower angles of take off that are reflected out from the hill. The ones absorbed in normal back yard antennas locations. See the paper in the ARRL Antenna Compendium series. Sorry I don't have the volume number here, but if you can find a table of contents, the title of the paper makes it clear it is a study of antennas on hills. Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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