Rudy Severns has many plots of elevated radial numbers, lengths, and
elevations on his web site antennasbyn6lf.com
My "T" showed the expected change in feedpoint Z as I added 125ft long
10ft elevated radials from 2 to the current 8. The last two made no
measurable difference. From Rudy's analysis they could/should be a bit
shorter than 125ft.
Another experiment with a prototype shorty vertical showed a big
reduction in Z when two 128' radials were raised from 4ft to 9ft,
confirming the NEC4 modeling.
Poor dirt here but a little bit better in winter when the ground is
totally water saturated. Also, the T is pretty much surrounded with
100ft plus firs and cedars absorbing RF. Another reason to love
verticals on the beach :) .
Grant KZ1W
On 12/11/2020 02:02, Artek Manuals wrote:
Jim et all
I agree with what you say on all points when it comes to radials on the
ground and salt water affects.
However I have always wondered about elevated radials . The NEC ( both 2
and 4) models (not that those are to always be trusted) show very little
(if any) improvement beyond four elevated radials, you have any theories
on why that is? Intuitively (also not to be trusted) that is a lot of
real estate in the spaces between
Dave
NR1DX
On 12/11/2020 4:37 AM, Jim Brown wrote:
On 12/10/2020 11:14 PM, Raymond Benny wrote:
With said, I believe my ground absorption is very high so I feel the
higher
numbers of radials helps greatly with my vertical efficiency and
radiation.
Hi Ray,
The soil affects us in two important ways. First, poor soil burns
transmitter power underneath the antenna and it's near field. We use
radials to shield the soil from the field, and to supply a low
impedance path for return current. Magnetic fields produced around
each radial by virtue of current flow couples loss in the earth into
the radials in the form of series resistance. Loss in each radial is 1
squared R; each time we double the number of radials the current in
each is divided by two, so the power coupled to the earth by each
divides by four. So the more radials, the less power is coupled to the
earth. THAT'S why more is better. The result of all this is that loss
in the soil under the antenna reduces the total strength of our signal
by that amount.
The second effect of soil is in the far field, where we field radiate
hits the earth and is reflected by it to form the vertical pattern.
The better the conductivity THERE, the our pattern will be both
stronger and at a lower angle. An antenna with its base just above sea
water is the extreme example of this -- the reflection is extremely
strong, and it is at a VERY low angle.
We can help the first of these two effects with a good radial system,
but the only thing we can do about the second (the far field
reflection), is to move where there is better soil. Most of us live
where we do because we like living there for reasons other than radio.
And that includes me and my XYL.
73, Jim K9YC
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