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## [TowerTalk] RE: TowerTalk Digest, Vol 22, Issue 80

 To: [TowerTalk] RE: TowerTalk Digest, Vol 22, Issue 80 "Dudley Chapman" Fri, 22 Oct 2004 14:58:13 -0400
 ```Scott, Scott, Yes, the literature about radials can be confusing unless you keep in mind an important distinction. In the case of an elevated 1/4 wave vertical, the main purpose of radials is to make up the other 1/4 wavelength so the antenna becomes like a 1/2 wave vertical dipole. The radials make the antenna resonate and gives the feedpoint something to work against. So, if you ignore the losses you can use full length elements for the vertical and the radials, or use loaded shortened ones, like hamsticks. When you use a 1/2 wave vertical against the ground, however, the ground forms the other half of the dipole, but not because it is resonant, but because it is for all practical purposes an infinite ground plane. In this case the main purpose for radials is to increase the ground conductivity. As such, consideration for the size and number of radials in the elevated vertical case is very different than for the ground mounted vertical case. In the ground mounted case, it's the amount of covereage of the wire in the ground in the near field of the antenna that makes the difference. So, where hamsticks are practical (although lossy) radials in an elevated vertical, they would add no value to a ground mounted vertical. Since its surface area coverage you need, the more long wires going out from the base of the antenna the better. How many and how long is determined by some simple rules of thumb and usually limited by what you think is a good cost (or hassle) for a given benefit. Typically 20 to 100+ radials that vary in length from 1/8 to 1/4 wavelength is the range most hams work in. By measuring the feedpoint resistance of the antenna as you add radials, you can watch it drop from 60+ (full 1/4 wavelength vertical) ohms with no radials towards the ideal of around 32 ohms. However, the curve shows diminishing returns, so at some point you see that the next added set of radials produces a small enough gain so that you declare it Miller Time. The lengths of each radial is very non-critical so if some have to be shorter than others due to real estate considerations, its perfectly ok. One caveat, though. The scenario above, of bringing 60 ohms down to 32 ohms applies to a vertical element that is physically close to 1/4 wave. In that case, the approx. 32 radiation resistance of the vertical element radiates half the power and the rest goes into heating up the 30+ ohms of ground resistance. As you add radials, you decrease the ground resistance to a few ohms so that a small percentage of the energy goes into the ground and the rest goes into space. However, a shortened loaded vertical like a hamstick has a very low radiation resistance in the area of a few ohms or so. That means that you have to have a ground system whose resistance is in the tenths of ohms to get good efficiency. Now you are talking about a very ambitious project that is much more work than putting up a longer vertical element. I would recommend against the hamstick vertical on the ground approach, unless you feel you are very limited in what you can deploy. On the other hand, I had a lot of fun doing 40m CW mobile using a hamstick on a long commute for a number of years. A good mobile hamstick installation is about 10 - 15% efficient, but is sure a lot of fun. Anyway if that is your intent, you might want to rethink it. Regardless of the answer, the one thing I can say for sure is that hamsticks would add no value as on-ground or underground radials. Dudley - WA1X Message: 4 Date: Fri, 22 Oct 2004 01:30:49 -0500 From: "Scott Fike" Subject: [TowerTalk] Ground radials- the long and short of it To: towertalk@contesting.com Message-ID: Content-Type: text/plain; format=flowed Pertaining to a ground-mounted vertical antenna with buried radials a few inches below the surface of the grass: Do ground radials have to be electrically the same length as the main vertical radiator element? Example: Take a 1/4 wave 80 meter hamstick stuck vertically in the ground. An 80 meter hamstick is physically about 6' tall but has about 60' of wire wound hellicaly around its 6' core insulator rod. Would it be better to make my ground radials using hamsticks (with their 60' of wire but physically still 6' long overall) or can I use 6' pieces of wire to match the hamsticks physical overall length or should one string out 60' radials? Some books I've read say: ".... make the ground radials 1/4 wavelength long to match the main 1/4 wavelength long vertical element". Other books and sources say: "..... just make the ground radials as long as you can to fit in the availible space in your yard". Scott, KC0BUS ________________________________________ _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] RE: TowerTalk Digest, Vol 22, Issue 80, Dudley Chapman <= Re: [TowerTalk] RE: TowerTalk Digest, Vol 22, Issue 80, Tom Rauch [TowerTalk] RE: Ground radials- the long and short of it, Dudley Chapman