Hi George,
Maybe that?s why this is done so seldom ? the 32.5% saving in copper has not
been worth the extra trouble.? With copper prices where they are now ? maybe it
would pay off ? particularly if you wanted to do what we did at K4JA.? The 9
circle 80M vertical array there had 100 100ft radials under each of the 9
antennas.? That?s 90,000 feet (about 18 miles) of wire.? It took all summer to
put it down, but it sure did work good!
Terman, Kraus, LaPorte and others are on the bookshelf here as well.? I have a
few radio rooks from the 20s and 30s that have remarkably good and accurate
descriptions of how things work ? as valid today as ever.
Best 73,
Hal
N4GG
-----Original Message-----
From: w4buw at aol.com [mailto:w4buw at aol.com]
Sent: Friday, August 24, 2007 11:25 PM
To: halken at comcast.net
Subject: Re: [SECC] Reference for radial discussion
Hi, Hal... just ran some quick number crunching based on your description of
the circular tie-ring radial grid, and come up with the following:
Center to first ring: 16x33= 528
First ring to second: 32x33=1056
Second ring to 100ft: 64x34=2176
Total radial lengths: 3760
Tie ring 1: =piD1=3.14x 66=207.24
Tie ring 2: =piD2=3.14x132=414.48
Total Tie ring length: 621.72
Total wire length: 3760+621.72=4381.72 ft
For 64-100ft radials: 64x100=6400 ft
4381.72/6400=.6846..., or roughly 68.5%
I suspect the roughly 55% comes from just the radial length, which comes out
58.75%, if you do not count the need for the tie rings...
I'm an old retired EE who got this call when still 12 yrs young, and will be 69
next birthday. Many changes in the hobby, but still enjoy the number
crunching, HI!
As you know, the key is to improve the ground system efficiency in order to
reduce that portion of the antenna system losses. Part of the consideration is
the dimensions between ground system conductors as compared to the wavelength
at the operating frequency. Yes, I also enjoy Terman, Jasik, and LaPorte, as
well as Kraus.
73 de George, W4BUW (SECC, SC)
-----Original Message-----
From: Hal Kennedy <halken at comcast.net>
To: secc at contesting.com
Sent: Fri, 24 Aug 2007 4:48 pm
Subject: [SECC] Reference for radial discussion
The concentric radial approach I mentioned I thought was discussed within the
564 page book: Radio Antenna Engineering, by LaPorte. This is a classic and
good addition to anyone?s antenna library ? particularly considering the price
? free.
Go to www.lulu.com <http://www.lulu.com/> and type ?Antenna Engineering? into
the search box. It?s the first book returned in the search. You can download
all 33Meg for free.
Meanwhile, I can?t find the particular radial approach I was thinking of in the
book, although many different radial schemes are discussed.
Concentric system:
The problem with radials that simple radiate out from a central point is that
they do not cover each square meter of ground equally well. They are spaced
far apart at the ends and tightly bunched at the center. To get a ?really
good? radial system it is sometimes recommended that 120 radials be used or the
ends be no more than 0.02 wavelength apart ? broadcasters frequently use 120.
For the first few feet from the tower its nothing but solid copper and most of
this is wasted. The alternative is as follows:
Suppose you want a 64 radial system of 100 foot radials. Place a concentric
circular loop wire 33 feet out from the center and another 66 feet out from the
tower. Connect 16 radials from the center to the fist ring wire, 32 radial
wires from the first ring wire to the second, and 64 wires outward from the
outer ring wire to 100 feet. In all cases the wires should be equally spaced
around in azimuth angle. This system will use around 55% as much copper as 64
full sized radials (I forget the exact ratio) and yield the same performance.
Soldering all the wires to the ring loops however, is a lot of extra work. If
its going to be in or on the ground for a long time then regular solder should
not be used either ? it should be silver solder.
73
Hal
N4GG
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