By the way, Tom
A 40 m 1/4 wave over 4 elevated radials should be a really good performer. I
built one that was a good match into Asia and other "faraway places" when
compared to my full-size 1/2 wave 40m vertical dipole. Couldn't tell any
really noticeable difference when switching back and for the between the two
and doing A/B comparisons on long-haul paths. - FWIW (The base of the 40m
vertical was up about 20 feet.)
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Charlie
Cunningham
Sent: Saturday, January 25, 2014 9:05 PM
To: 'Tom W8JI'; topband@contesting.com
Subject: Re: Topband: Grounding the ends of radials
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@contesting.com] On Behalf Of Tom W8JI
Sent: Saturday, January 25, 2014 8:47 PM
To: topband@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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