One of the earlier postings suggested that the quarterwave vertical antenna
with radials was elementary and easy to understand. I have never found this
antenna easy to understand.

RF experts on this newsgroup cannot agree on whether i) the radials reflect
the wave or ii) the field from the radials cancels out. The standard
academic books show that the principle behind the vertical ground plane
antenna is that the vertical radiating element emits the wave, and is
reflected by the ground plane.

You can view a conductor as having current pushed through it by a RF source,
or the current can be induced in the conductor by the wave. This is a
boundary condition in Maxwell's equations, referred to in theory of
transmission lines and guided waves.

You can view the radials as reflecting the wave and having current induced
in them, or they can have current pushed through them by the RF source. This
is probably the same thing, due to the arrangement of all antenna parts
forming the antenna impedance. In image theory, the impedance comes from
both the self impedance and the mutual impedance.

It appears that a single counterpoise wire is connected to the RF ground
side to provide a conductor for that side and be a form of dipole. If a
proper RF ground is not provided, the result may be RF in the shack e.g. the
RF tries to return via mains wiring. Does connecting several wires make the
RF ground side less live i.e. occupying a larger area to be more of a
reflector and thus dissipative? If a RF ground is live, it can be dangerous
to touch it. Do you increase the area of RF ground to make it less dangerous
to touch e.g. radials under a carpet when relatives and pets are about?

The theory behind the quarterwave vertical is the monopole above a ground
plane, where the ground plane reflects the wave emitted by the vertical.
The monopole is explained using image theory. In practice, the ground plane
is
replaced by radials. Do the radials reflect the wave then?

The reflecting element on a Yagi manages to reflect most of the wave. The
reflecting element on a Yagi is a parasitic element that has an impedance
to cause the wave emitted by the driven element to flow in a particular
direction. A Yagi normally has only one reflector. Although the reflector
is in the near field of the Yagi, can a comparison be made with the radials
of
a quarterwave vertical antenna? The reflector on a Yagi is usually a thin
tube with lots of air (gap) around it. Even though it occupies a small
area, it still manages to reflect most of the wave. Yagi has a Front to
Back
ratio in dB.

Radials can be tuned. Some antennas have loading coils in the radials.


Antenna theory is often about wires and metallic items reflecting waves,
and the phase of the reflected wave. The phase of the reflected wave can be
constructive or destructive, affecting the impedance of the antenna. If an
antenna is mounted too close to the ground, the reflected wave cancels out
the emitted wave.

Because a ground plane reflects the wave, the impedance of an antenna can
vary with height.

Parastic elements on a Yagi have a mutual impedance to each other. Would
you regard the radials on a quarterwave vertical as having a mutual
impedance?

The radials increase the conductivity below the radiating element,
decreasing ground losses. The radials are regarded as a finite or imperfect
ground plane.

References:
"Antenna Theory and Design" by Warren Stutzman and Gary Thiele. pages 66 to
68. Practical monopole with radial wires to simulate a ground plane.
"Antenna Engineering Handbook" by Richard C. Johnson. Radials suppress
currents from flowing on outside of coax. p 28. If the ground is imperfect,
the perfect reflected image is mutiplied by a complex ground reflection
coefficient. The ground has a mutual impedance.
"Antenna Theory" by Professor Constantine Balanis. Second Edition p 165. A
ground plane formed by a perfect conductor completely reflects the wave. If
the ground is finite i.e. not as conductive, it still reflects the wave but
not as well. The conductivity determines the quality of the reflection.

All antennas consist of conductors which have current conducted to them
from sources and induced in them by coupling to fields from other
conductors or other parts of the same conductor. These currents create
fields. Ground plane antennas work exactly the same as all others. In
that way they're simple to understand.

Yes, you can view it this way or that, with various degrees of accuracy
and inaccuracy. The problem is that people begin to believe that the
alternate views are really what happens, rather than attempts at
simplifying and understanding things. Before you know it, you've got
mirrors, "ground" high above the Earth, impossible reflections, and
other dubious concepts which end up leading people farther and farther
from really understanding the basic principles involved.

Roy Lewallen, W7EL

David wrote:
One of the earlier postings suggested that the quarterwave vertical antenna
with radials was elementary and easy to understand. I have never found this
antenna easy to understand.

RF experts on this newsgroup cannot agree on whether i) the radials reflect
the wave or ii) the field from the radials cancels out. The standard
academic books show that the principle behind the vertical ground plane
antenna is that the vertical radiating element emits the wave, and is
reflected by the ground plane.

You can view a conductor as having current pushed through it by a RF source,
or the current can be induced in the conductor by the wave. This is a
boundary condition in Maxwell's equations, referred to in theory of
transmission lines and guided waves.

You can view the radials as reflecting the wave and having current induced
in them, or they can have current pushed through them by the RF source. This
is probably the same thing, due to the arrangement of all antenna parts
forming the antenna impedance. In image theory, the impedance comes from
both the self impedance and the mutual impedance.
. . .

"Not everything that can be counted counts, and not everything that
counts can be counted."
- Albert Einstein (1879-1955)


Zen


Roy Lewallen wrote:


All antennas consist of conductors which have current conducted to them
from sources and induced in them by coupling to fields from other
conductors or other parts of the same conductor. These currents create
fields. Ground plane antennas work exactly the same as all others. In
that way they're simple to understand.

Yes, you can view it this way or that, with various degrees of accuracy
and inaccuracy. The problem is that people begin to believe that the
alternate views are really what happens, rather than attempts at
simplifying and understanding things. Before you know it, you've got
mirrors, "ground" high above the Earth, impossible reflections, and
other dubious concepts which end up leading people farther and farther
from really understanding the basic principles involved.

Roy Lewallen, W7EL

David wrote:
One of the earlier postings suggested that the quarterwave vertical
antenna
with radials was elementary and easy to understand. I have never found
this
antenna easy to understand.

RF experts on this newsgroup cannot agree on whether i) the radials
reflect
the wave or ii) the field from the radials cancels out. The standard
academic books show that the principle behind the vertical ground plane
antenna is that the vertical radiating element emits the wave, and is
reflected by the ground plane.

You can view a conductor as having current pushed through it by a RF
source,
or the current can be induced in the conductor by the wave. This is a
boundary condition in Maxwell's equations, referred to in theory of
transmission lines and guided waves.

You can view the radials as reflecting the wave and having current
induced
in them, or they can have current pushed through them by the RF
source. This
is probably the same thing, due to the arrangement of all antenna parts
forming the antenna impedance. In image theory, the impedance comes from
both the self impedance and the mutual impedance.
. . .

The vertical element is connected to the centre conductor (RF live). The
radials are connected to 0V on the transceiver.

If only the vertical is connected, the antenna still radiates although not
as well. If only the
radials are connected, the antenna does not radiate because the radials are
connected to 0V and not a varying voltage.

With both vertical and radials connected, the vertical element radiates the
wave. The wave is reflected by the radials as boundary condition of
Maxwell's equations. The reflection induces a current in the radials. This
current has a standing wave on it.

Do you think the above is correct? All parts of the antenna form the
impedance. Without radials, the impedance is poor and the vertical element
does not radiate well.

Other explanations say that displacement currents go through the air and
terminate on the radials. The displacement currents then becomes conduction
current in the radials. Displacement current is another anomaly with
electromagnetic theory.

I notice that two people have simulated the vertical antenna with radials
using EZNEC, and obtained different results. One simulation shows that the
radials radiate, the other shows that they do not.

The vertical element is connected to the centre conductor (RF live). The
radials are connected to 0V on the transceiver.

No. They're connected to the shield/braid of the feedline. There's
no assurance that this point will be at "0V" with respect to anything
in particular except itself, and in particular it usually won't be at
0 volts with respect to the transceiver's chassis / output jack
(except perhaps momentarily, twice per RF cycle).

If only the vertical is connected, the antenna still radiates although not
as well.

.... because the outside of the feedline will tend to act as a
poorly-tuned radial/counterpoise.

If only the
radials are connected, the antenna does not radiate because the radials are
connected to 0V and not a varying voltage.

With both vertical and radials connected, the vertical element radiates the
wave. The wave is reflected by the radials as boundary condition of
Maxwell's equations. The reflection induces a current in the radials. This
current has a standing wave on it.

Do you think the above is correct?

Not really, no. It's a mistake to think that the radials "are
connected to 0V and not a varying voltage". You're falling into the
trap of thinking that "ground" is some sort of magical "zero volt"
reference which is the same everywhere. That isn't true even at DC,
and it's certainly not true at RF!

All parts of the antenna form the
impedance. Without radials, the impedance is poor and the vertical element
does not radiate well.

The vertical element radiates very well indeed... it'll radiate all of
the power which is fed into it, except for a small amount of loss.

The problem isn't that it doesn't radiate. The problem is that it's
difficult to feed power into it, much of the time.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Tue, 18 Jul 2006 20:34:32 +0100, "David" nospam@nospam wrote:

If only the vertical is connected, the antenna still radiates although not
as well. If only the
radials are connected, the antenna does not radiate because the radials are
connected to 0V and not a varying voltage.
snip
I notice that two people have simulated the vertical antenna with radials
using EZNEC, and obtained different results. One simulation shows that the
radials radiate, the other shows that they do not.

Hi Dave,

Your statements above show a serious problem with understanding the
operation of antennas.

The radials are not potted plants merely arranged along the ground (or
in the air) to give a sense of symmetry and balance.

You would go further to engage more in dialogue rather than simply
posting statements. Much of the utility of radials has been
discussed, revisited, and rehashed to no apparent effect against what
you offer above. The last sentence is outrageously wrong for any of a
number of reasons (or proof of some pretty stupid simulation).

73's
Richard Clark, KB7QHC

Agreed, the centre junction of the radials is not always at 0V. Current
flows along the coax braid on the inside, meaning that the inside part of
the coax braid and radials junction can be any voltage. The radials have a
voltage gradient along them because of the standing wave. Because the return
current flows on the inside of the coax braid, it is normally safe to touch
or go near the outside of the braid. For permanent low installations in a
public area, coax should be used instead of twin feeder. The fact that the
return current flows on the inside of the braid gives coax its shielding
properties.

On Tue, 18 Jul 2006 21:32:13 +0100, "David" nospam@nospam wrote:

Agreed, the centre junction of the radials is not always at 0V.

Hi David,

In isolation, this statement offers nothing at all, unless, of course,
you are talking about an unexcited system. The notion that 0V
inhabits some greater portion of the antenna, or its radials, or its
junction is a strange concept to its normal operation.

David, AE6EO, has similar concerns that you are presenting what I
would call a naive representation of radiators.

Current
flows along the coax braid on the inside, meaning that the inside part of
the coax braid and radials junction can be any voltage. The radials have a
voltage gradient along them because of the standing wave.

In that sense, 0V does reside at some favored points, but this is not
an explanation of anything.

Because the return
current flows on the inside of the coax braid, it is normally safe to touch
or go near the outside of the braid. For permanent low installations in a
public area, coax should be used instead of twin feeder. The fact that the
return current flows on the inside of the braid gives coax its shielding
properties.

Is this germane to a particular point? Again, these are simply
statements, and they appear unconnected to any kind of dialog.

73's
Richard Clark, KB7QHC

However, I still think that with only the vertical element connected to the
centre conductor, the vertical element radiates although not very well. With
only the radials connected to the outer braid, the radials do not radiate.
The RF live of the transceiver is normally connected to centre conductor,
and the RF ground side (the 0V side) is normally connected to the braid. The
outer of the connector on the transceiver is possibly connected internally
to the case and mains Earth.

On Wed, 19 Jul 2006 20:33:29 +0100, "David" nospam@nospam wrote:

However, I still think that with only the vertical element connected to the
centre conductor, the vertical element radiates although not very well. With
only the radials connected to the outer braid, the radials do not radiate.
The RF live of the transceiver is normally connected to centre conductor,
and the RF ground side (the 0V side) is normally connected to the braid. The
outer of the connector on the transceiver is possibly connected internally
to the case and mains Earth.

Hi David,

Only the slimmest margin of this comes close, and not enough to
explain anything. 0V, ground, live, dead, hot, cold, or whatever you
want to call it has long since disappeared from the scene at the other
end of a cable or twin lead. Radials do not mimic these terms even if
the illusion of continuity suggests otherwise. There is no "rf side"
nor is there a "ground side" to appeal to. Such distinctions are
reserved for very untechnical allusions.

73's
Richard Clark, KB7QHC