Topband: Grounding the ends of radials

[Charlie Cunningham]

All true, of course.

Aside from the rocky condition of my lot, one of the main reasons that I
rely on elevated radials is that I can model those antennas handily and I
get good measurable results that compare and agree pretty well with my 
EZNEC models. Especially useful in parasitic or phased arrays!

73,
Charlie, K4OTV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Tom W8JI
Sent: Saturday, January 25, 2014 8:47 PM
To: topband at contesting.com
Subject: Re: Topband: Grounding the ends of radials


>I generally agree with you, Bob - especially with regard to not grounding
> the far ends of 1/4 wave radials!!  After all what we are trying to
> establish is a low-impedance "image plane" for the vertical radiator to be
> fed against! A 1/4 wave wire, grounded at the far end would have a high
> impedance to ground at the base, or feed-point, of the antenna!  Makes no
> sense! Would not result in a very favorable "driving-point impedance!

The issue is complicated by the number of radials, the soil, and the radial 
length.
Even buried radials directly in contact with soil are "resonant", the extent

of which depends on the shallow and deep characteristics of the earth.  In 
most soils, bare wires are not grounded for RF as well as people probably 
think.

Measuring buried 40 meter radials here, I could get a fairly high base 
impedance with some radial lengths and numbers. This did **not** affect the 
field strength. With about a dozen radials the base impedance of a 40M 
vertical with long radials was about 50-60 ohms.  It had about the same 
measured field strength as 4 elevated resonant radials that had a base 
impedance down in the upper 30 ohm range.

People used to use ground rods at the ends of radials when they had to 
truncate the radials. Also, some people used ground rods and no radials at 
all. They swore by those systems, wrote articles about those systems, and 
even bragged about all the DX they worked.

Opinions, contacts, or feelings tells us more about how difficult it is to 
tell how well something really works than it tells us how the systems 
actually work. That's why this stuff rages on and on for decades.

Even the AM BC stuff was mostly meaningless nonsense. People would pull 
radials in over other radials while guessing not many of the old radials 
were still there, make measurements with 3 dB of wobble in the readings and 
pick the numbers they liked,  and call it conclusive evidence.

73 Tom 

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