>Help, Help!
>There have been many, many postings on how to set up the radials
<but never a discussion on why or how radials actually effect the
>radials as it seems to be "beyond the scope....".
not really beyond the scope, but often leading to long heated discussions.
>It is pretty easy to understand why from a circuit current loop viewpoint
>i.e. the transceiver power output is divided between the radiation resistance
>and the ground resistance (ignoring connector, coils, and wire resistance).
it does get a bit more complex than that, but thats enough for now.
>1. However the radiation resistance is a make-believe or psuedo resistance
>apparently derived from calculations of subtracting ground system power
>(system loop current x ground resistance) from the transceiver power output.
>Thus, since the loop current is known and the remaining power is known,
>then the radiation resistance can be calculated?
>But his seems analagous to lifting oneself up by pulling up on ones bootsraps!
The problem is that you have 2 things, neither of which is easy to measure in
the real world.
>2a. For vertical antennas, it is said that there is no reflection (radiation)
>from
>the ground system. It isn't very clear why, horizontal or vertical
>polarization or ?
well, there can be radiation from the ground system. using the term
'reflection' will
lead to lots of heated discussion as that implies certain things that normally
either
aren't true or are hard to visualize. the ground system normally can't be said
to
reflect anything, it can provide currents that may be visualized as images of
the
vertical element. in a well balanced ground system the currents on opposite
sides
cancel out so there may be no far field contribution from the ground system,
though
there may be near field effects.
>2b. It is also that radiation is a result of the changing state of the
>electrons in a
>material, caused by the changing current intensity. Thus the material is
>acting
>like a capacitor (charging and discharging as the current changes. For the
>material to charge/discharge there must be an opposite charge/discharge
>somewhere?
electrons aren't normally said to be 'changing state' in antennas or grounds.
they
are flowing from point to point but that is not normally refered to as a
'state' as
would be used in talking about energy bands or things like that.
the 'material' as in 'conductors' are not in themselves acting as a capacitor.
the
capacitor is between the various conductors using the air or soil as
dielectrics.
in the simplest form of a dipole there is obvious capacitance between the two
wires,
and also inductance along the wire itself. In a vertical with a ground plane
the
capacitance is between the vertical wire and the ground plane conductors.
>2c. Is this "somewhere" the ground or the radials? Do the radials allow the
>antenna material to charge/discharge to greater amounts? Why and how?
well, the bigger and more conductive the ground plane is the higher the
capacitance
should be. and the more conductive the ground plane is the lower the resistance
which lets you see more of the capacitance.
>3. If 2c is true then "heating up the ground comments" hides what is really
>happening?
no, energy must all be accounted for. so if it comes out of the transmitter
and isn't
radiated then it must be lost as heat and the most likely culprit is the
ground. of
course if there is a matching network or poor wire conductivity those are other
sources of loss as heat.
help help
k7puc
----- Original Message -----
From: Scott Myers
To: SteppIR@yahoogroups.com
Sent: Tuesday, May 17, 2011 5:42 AM
Subject: [SteppIR] Re: BigIR 20 meter issue.
snips
I never suggest less than 32 radials for good radiation efficiency.
As mentioned by others, resonance does not occur in ground radials, nor would
you want it to. That discussion is well beyond the scope of this thread. ,
Scott AC8DE
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