VERTICAL GROUND SYSTEMS

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From: QLF%mimi@magic.itg.ti.com
Date: Wed May 15 1996 - 12:52:23 EDT


From: Brad Bradfield QLF
 
Subj: VERTICAL GROUND SYSTEMS
 
Even though this isn't QRP related per se, it is a topic that continues to come
up here on the QRP-L, so let me attempt to give y'all some information to knaw
on. Sorry it's so long. Ok now, everybody put away your knives, guns and
flame throwers.
 
First off; verticals REQUIRE a ground system of some kind for PROPER operation.
Now unless your vertical is installed in the middle of a salt marsh or off
shore in the ocean (I've seen broadcast stations like that,) this probably
means radials.
 
Everybody's heard some amateur saying "My Butter-Hy-Mos vertical loads fine
without radials so I must not need them afterall." In the words of the
immortal Sherman T. Potter, "HORSE FEATHERS!" The books will show you that the
base impedance of the vertical will not change a whole lot with the addition of
any number of radials. Just because it LOADS ok doesn't mean that the
radiation efficiency is worth a can of beans. You could be QRPppp without
really intending to be.
 
The following will show the relative improvement in radiated field intensity
with an increasing number of 1/4 wavelength radials. Each line is referenced
to an antenna with two radials.(4) I wish I had a reference showing the
intensity with no radials, but I do not.
 
     NUMBER FIELD
       OF INTENSITY
     RADIALS IMPROVEMENT
------------------------------------
       2 REF
       15 2.7 dB
       30 3.4 dB
       60 3.9 dB
       113 4.2 dB
 
The following will show the relative improvement in radiated field intensity
with an increasing length of radials on a 1/4 wavelength vertical antenna with
113 total radials. Each line is referenced to a radial length of 0.125
wavelength.(4)
 
     LENGTH FIELD
       OF INTENSITY
     RADIALS IMPROVEMENT
------------------------------------
      0.125 REF
      0.25 2.1 dB
      0.375 2.5 dB
 
Common practice in the broadcast industry is to use 120 to 240 (90 minumum) 1/4
wavelength radials, often interspersed with a number of shorter radials. They
are typically #10 AWG bare copper, and are plowed into the ground. If you're
building a broadcast station, you will, of course, allow enough real estate to
install these radials. If you're sitting on a normal city lot, you won't have
this luxury. Install as many radials of whatever length is possible. And you
can always bend them to get around objects and/or to make them longer.
 
To answer the question that has also been asked in this discussion, I can find
no reference in any of my sources that gives me any information on using
insulated wire for radials. I've seen it done, and I've done it myself. It
works.
 
For more information, check the following:
 
1) The Amateur Radio Vertical Antenna Handbook by CAPT Paul Lee, N6PL
   CQ Publishing, Inc
   [Outstanding reference, but may or may not be still in print]
 
2) The Complete Broadcast Antenna Handbook by John E. Cunningham
   TAB Books
   [Out of print?]
 
3) Antenna Engineering Handbook by Johnson and Jasik
   Chapter 25
   McGraw-Hill
   [Expensive!]
 
4) Ground Systems as a Factor in Antenna Efficiency by G.H. Brown et al
   Proc. of the I.R.E., June 1957, p. 735
   [Find a library that has it]
 
Again, I apologize for the length of this posting, but thought it might answer
some of the continueing questions.
 
73's
 
Brad, WB0CGH
******************************************************************************
Brad Bradfield, PE Electrical Design Engineer
(H) 817-321-2960 Texas Instruments, Inc.
(W) 214-462-6230
 
QLF@MSG.TI.COM
WB0CGH@WO5H.#DFW.TX.USA.NA
ARRL Life Member QRP-L #377 SMIRK #4906 IEEE(M) ARS #72
Collector of wireless and landline Morse keys and accessories.
******************************************************************************
 


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