To: | schiers@netins.net, towertalk@contesting.com,jimlux@earthlink.net |
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Subject: | Re: [TowerTalk] re Radials |
From: | "Rob Atkinson, K5UJ" <k5uj@hotmail.com> |
Date: | Wed, 14 Jun 2006 16:47:05 +0000 |
List-post: | <mailto:towertalk@contesting.com> |
the davis RF price for #16 looks pretty good by current pricing however I am
a bit leery of the physical robustness of #16. WOR reportedly tried aluminum at one time and it didn't work out for some reason. Maybe the Al didn't last. you might think $68 for 1K' isn't bad but if you are putting down 100 1/4 w. radials for 160 it starts getting pricey for a ham. do the arithmetic. re the 20' radials--a base fed linear conductor perpendicular to earth comes under the effect of earth when close, so that earth becomes the mirror part, or the missing other half of the radiator. the massiveness of the earth predominates so that any radials buried or laid on the surface aren't the "mirror part" so much as they facilitate earth return conductivity by helping overcome resistance of earth ground. Because of that their length isn't quite as critical. If you could levitate the radiator up into the air to sufficiently isolate it from earth's surface, then any metal component (we'll continue to use radials) intended to be the lower half, or mirror, must perform all of the counterpoise or groundplane function and because it is a complete antenna component, its length matters. This is why if you place your radiator up say, 10 feet on 40 m. the radial lengths have to be measured and cut appropriately. Studies (I know of at least one IEEE paper on this) have shown that unusually short radials on the ground or below grade work almost as well as 1/4 or 1/2 w radials, but in this case, "short" meant 45 degrees or 1/8 w. I think 20 feet is pushing the short envelope. Also, it is critical that you employ lots of radials to enjoy the benefit of having them. Five or ten or twenty is not enough. From what I have read, if you put down ninety radials around 60 feet long, you will enjoy almost the same field strengh in mv/meter at one km you would have with the same number of radials 1/4 w. long on 160 meters. Most hams who find ground mounted verticals to be poor performers simply do not use enough radials. rob / k5uj From: "hasan schiers" <schiers@netins.net> To: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>,<towertalk@contesting.com>,"Jim Lux" <jimlux@earthlink.net> Subject: Re: [TowerTalk] re Radials Date: Wed, 14 Jun 2006 09:13:21 -0500 But....aluminum in a lot of soil types will disintegrate in a couple of years, so best to know the soil characteristics before making the effort to lay a bunch of aluminum down. 68 bucks for a 1000' of #14 THHN insulated copper wire is not a fortune, and would last a very long time. 73, ...hasan, N0AN ----- Original Message ----- From: "Jim Lux" <jimlux@earthlink.net> To: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>; <towertalk@contesting.com> Sent: Wednesday, June 14, 2006 8:56 AM Subject: Re: [TowerTalk] re Radials At 06:29 AM 6/14/2006, Rob Atkinson, K5UJ wrote:It depends on whether or not you either bury them, lay them flat on the ground or elevate them a significant distance in terms of wavelength. If you bury them or lay them on the ground the 40 meter 1/4 w/l will be okay on 20. If you elevate them (for 7 mhz 6 feet would probably be okay) then I think you need radials cut to each band you want to operate. _________________________________________________________________ Is your PC infected? Get a FREE online computer virus scan from McAfee® Security. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963 _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk |
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