Richard Clark wrote:
On Thu, 22 Jan 2009 13:43:19 -0800, Jim Kelley
wrote:

separately the magnetic and electric fields associated with a radio signal
I perceive that the quote says nothing about "field separation" -

Now that is getting "précis."

73's
Richard Clark, KB7QHC

c'est exact

Do you claim to have separated voltage from current whenever you measure
one or both?

ac6xg

On Jan 22, 6:32*am, Cecil Moore wrote:


I'm not talking about coaxial loops. I'm talking about
coils of wire wrapped around a ferrite rod typical of
AM radios. Seems pretty obvious it is responding to the
magnetic field when it needs to be at right angles to
the transmitting monopole (or dipole).
--
73, Cecil *http://www.w5dxp.com

I don't see how you could be receiving the magnetic
field if say you are 150 miles away from the station.
I looked around on the web for other opinions, and
ran across a page from W8JI.
http://www.w8ji.com/magnetic_receiving_loops.htm
I tend to agree with him.
Here is one quote that seems to fairly well explain
the position.

From W8JI web page..
"Acceleration of charges causes a very unique force
on other charges in the Universe. We call this effect
electromagnetic radiation. It is a totally different effect,
and it is independent of induction fields. This is the only
effect or force that works to move charges at a very
large distance, and it cannot be created by mixing
induction fields. "

Anyway, that's about as good an explanation as I
can find as to why I don't believe in "magnetic" antennas,
except for the properties at very close distances.
At any greater distance beyond about 1/10 wavelength,
it all goes out the window.
That's the way I see it on January 22, 2009 at 7:55 in
the PM. :/

On Jan 21, 8:59*pm, Richard Clark wrote:


Hi Mark,

That would seem to indicate you seriously unbalanced the antenna by
the side feed which is geometrically unbalanced. *For instance, the
line doesn't lead off horizontally for any great distance, does it?

Of course, this all hinges on what you mean by not "near as well."

Not sure.. I don't the the position of the feed line should
have been a problem, but it's been so long since I tried it,
I forgot what happened. I just seem to remember trying it
one time, and stuck with the bottom feed.
I'll have to try it again later. I could use my circular 16 inch
dia loop. It's small enough I can easily hold it and shift the
polarization just by rotating it.

"Jim Kelley" wrote in message
...
Richard Clark wrote:
On Thu, 22 Jan 2009 13:43:19 -0800, Jim Kelley
wrote:

separately the magnetic and electric fields associated with a radio
signal
I perceive that the quote says nothing about "field separation" -

Now that is getting "précis."

73's
Richard Clark, KB7QHC

c'est exact

Do you claim to have separated voltage from current whenever you measure
one or both?

ac6xg


Isn't the point that an electromagnetic wave can be considered in terms of
the E or H fields associated with it, or indeed both at the same time? If
any power is extracted from the wave then this will involve E and H, or
voltage and current, simultaneously. And when the wave encounters a region
of space with effective relative permittivity or permeability different from
the free-space values, the ratio of E to H changes; that is, the intrinsic
impedance, Zo changes locally. The work I described earlier contributed to
the development of propagation prediction methods for medium and long wave
transmissions and an example of a region of space that exhibits a
particularly inductive effect is a built-up city with many tall buildings.

I'm aware of issues involved in claiming generation of separate E or H
fields, as has been described by Kabbary et al in their 'crossed-field
antenna', but surely the issues concerning a receiving antenna are
different? A very short monopole attached to a high-input-impedance
amplifier, for example (i.e. an 'active' antenna), should have very little
effect on the local intrinsic impedance, yet it should produce a signal
proportional to the magnitude and sign of the local E field, whatever the
local H field strength. Equally, a small-diameter well-screened loop should
be capable of measuring the local H-field strength without altering the
local Zo. In these cases, 'short' and 'small' are relative to the
wavelength.

Rohde & Schwarz used to sell an HF diversity receiving antenna system based
on an array of small screened loops, the screens of which were applied
(separately) as active monopoles. This provided somewhat separate reception
of the E and H fields associated with the incoming radio wave and, from what
I've heard, it worked - it provided some degree of 'diversity gain'.
However, this was an array requiring a sizeable amount of clear land.

Perhaps the difference is that what I described before was for use with
broadcast signals (following the topic of the OP), in which case short and
small antennas can be used for measurement purposes within areas provided
with adequate (or nearly adequate) field strength, whereas in amateur radio
applications the tendency would be to use as large an antenna as possible,
to maximise the possible range.

Chris

wrote in message
...
On Jan 22, 6:32 am, Cecil Moore wrote:


I'm not talking about coaxial loops. I'm talking about
coils of wire wrapped around a ferrite rod typical of
AM radios. Seems pretty obvious it is responding to the
magnetic field when it needs to be at right angles to
the transmitting monopole (or dipole).
--
73, Cecil http://www.w5dxp.com

I don't see how you could be receiving the magnetic
field if say you are 150 miles away from the station.
I looked around on the web for other opinions, and
ran across a page from W8JI.
http://www.w8ji.com/magnetic_receiving_loops.htm
I tend to agree with him.
Here is one quote that seems to fairly well explain
the position.

From W8JI web page..
"Acceleration of charges causes a very unique force
on other charges in the Universe. We call this effect
electromagnetic radiation. It is a totally different effect,
and it is independent of induction fields. This is the only
effect or force that works to move charges at a very
large distance, and it cannot be created by mixing
induction fields. "

Anyway, that's about as good an explanation as I
can find as to why I don't believe in "magnetic" antennas,
except for the properties at very close distances.
At any greater distance beyond about 1/10 wavelength,
it all goes out the window.
That's the way I see it on January 22, 2009 at 7:55 in
the PM. :/


Could I suggest taking a look at one of the well regarded text books such as
'Antennas' by J. Kraus. Your local library may be able to get it in for
you. There you'll find it well explained that 'electromagnetic radiation',
a radio wave, has associated with it an electric field and a magnetic field.
Each is measurable and is a manifestation of the radio wave - it's probably
incorrect to say, the other way round, that the radio wave is formed by the
'radiation' E and H fields. Drawing power from a radio wave in order to
operate a radio receiver can be done using either an antenna sensitive to
the local E field strength, such as a whip or many types of wire antennas,
or using an antenna sensitive to the local H field strength, such as a
loop - i.e. a magnetic antenna. It may be argued that either would have
some effect on the other field, but this may not be very important in
practice.

These radiation fields alternate in time with one another, in sync with the
current in the antenna, but the phase of their alternation is (obviously)
retarded with distance away from the antenna - because of the limited speed
of propagation of a radio wave. They are directed transverse to the
direction of propagation and are oriented perpendicularly to one another in
that transverse plane.

'Induction' and 'electrostatic' reactive fields are found close to a
transmitting antenna, but these decay with the square or cube of the
distance and at distances greater than wavelength/2*Pi they are weaker than
the radiation field.

I hope this helps a bit.

Chris

On Jan 22, 8:26*pm, "christofire" wrote:


Perhaps the difference is that what I described before was for use with
broadcast signals (following the topic of the OP), in which case short and
small antennas can be used for measurement purposes within areas provided
with adequate (or nearly adequate) field strength, whereas in amateur radio
applications the tendency would be to use as large an antenna as possible,
to maximise the possible range.

Chris

No real difference. The objective is improving the s/n ratio.
With any kind of array the main improvement is going to be
from a directive pattern and the use of nulls. Only if you had
a very close noise source might it be useful to use the properties
of the small loops, etc to reduce reception of the magnetic field.
There is a small increase in overall s/n ratio as you increase the
size of a small loop, but it's not anything earthshaking.
In the city, for all practical purposes my 16 inch round loop
has just about as good a usable s/n ratio as my larger
44 inch per side diamond loop.
You have to get into a low noise environment to really take advantage
of the small benefits of a larger loop.
IE: in the dead of the winter it will be more useful than in the
noisy
summer.
On those low frequencies, it doesn't take much to get to the
saturation point where adding "more" really doesn't do much to
improve the s/n ratio.
As mentioned before, if you are tuned to a dead frequency and
you can hear the atmospheric noise, you are already basically
to the point where adding "more" is not going to help.
At that stage only changing the pattern will improve s/n ratio.
And on MW, it's usually the nulls that are used, vs the gain
in a certain direction.

On Jan 22, 8:46*pm, "christofire" wrote:
*Drawing power from a radio wave in order to
operate a radio receiver can be done using either an antenna sensitive to
the local E field strength, such as a whip or many types of wire antennas,
or using an antenna sensitive to the local H field strength, such as a
loop - i.e. a magnetic antenna. *It may be argued that either would have
some effect on the other field, but this may not be very important in
practice.


Well, that's my whole point. If the station you are listening to
is 150 miles away, I don't see how the local fields will really
come into play.

On Fri, 23 Jan 2009 02:26:48 -0000, "christofire"
wrote:


"Jim Kelley" wrote in message
...
Richard Clark wrote:
On Thu, 22 Jan 2009 13:43:19 -0800, Jim Kelley
wrote:

separately the magnetic and electric fields associated with a radio
signal
I perceive that the quote says nothing about "field separation" -

Now that is getting "précis."

73's
Richard Clark, KB7QHC

c'est exact

Do you claim to have separated voltage from current whenever you measure
one or both?

ac6xg


Isn't the point that an electromagnetic wave can be considered in terms of
the E or H fields associated with it, or indeed both at the same time? If
any power is extracted from the wave then this will involve E and H, or
voltage and current, simultaneously. And when the wave encounters a region
of space with effective relative permittivity or permeability different from
the free-space values, the ratio of E to H changes; that is, the intrinsic
impedance, Zo changes locally. The work I described earlier contributed to
the development of propagation prediction methods for medium and long wave
transmissions and an example of a region of space that exhibits a
particularly inductive effect is a built-up city with many tall buildings.

Well, this removes us from the Byzantine parsing between "separation"
and "separately."

If by the addition of these buildings you propose that characteristic
of "space" has become intrinsically different - I suppose. However,
your having made that observation, what of it?

I'm aware of issues involved in claiming generation of separate E or H
fields, as has been described by Kabbary et al in their 'crossed-field
antenna', but surely the issues concerning a receiving antenna are
different?

Ah! We return to -separate- fields as if there were some distinction
in their labels that now devolves to the discussion of the cfa. As
the cfa lacks credibility beyond having an invented nomenclature, this
does not elevate the discussion of -separate- fields to any great
distinction.

A very short monopole attached to a high-input-impedance
amplifier, for example (i.e. an 'active' antenna), should have very little
effect on the local intrinsic impedance, yet it should produce a signal
proportional to the magnitude and sign of the local E field, whatever the
local H field strength.

However? That adverb generally proceeds from a premise and introduces
a counter argument which is not developed here.

"should have very little effect on the local intrinsic impedance?"
This drops into the dialog without any sense of proportion as it is a
qualification and the rest of this lacks quantification. How much is
the effect, how much is little, and more so, how much is very little?
Without quantifiables your impression of "little" may in fact be quite
large and fully expected.

Equally, a small-diameter well-screened loop should
be capable of measuring the local H-field strength without altering the
local Zo.

Should? You write these as mandates, but using weak verbs. This is
the writing of disappointment about vague expectations. Why not use
the verb "must?" Perhaps because you would then be expected to
provide a quantified value instead.

All measurements disturb what they measure. If you cannot express the
degree, you don't have a measurement, it is a guess.

In these cases, 'short' and 'small' are relative to the
wavelength.

Rohde & Schwarz used to sell an HF diversity receiving antenna system based
on an array of small screened loops, the screens of which were applied
(separately) as active monopoles. This provided somewhat separate reception
of the E and H fields associated with the incoming radio wave and, from what
I've heard, it worked - it provided some degree of 'diversity gain'.
However, this was an array requiring a sizeable amount of clear land.

This still does not provide evidence of the supposed "separate
reception of the E and H fields." The performance described is rather
more ordinary and requires no elaboration.

Perhaps the difference is that what I described before was for use with
broadcast signals (following the topic of the OP), in which case short and
small antennas can be used for measurement purposes within areas provided
with adequate (or nearly adequate) field strength, whereas in amateur radio
applications the tendency would be to use as large an antenna as possible,
to maximise the possible range.

Well, this last apologia doesn't even hold up under scrutiny standing
by itself, much less supporting anything that came before it.
"the tendency would be to use as large an antenna as possible,
to maximize the possible range." is another qualified statement in
that "as large as possible" spans many interpretations, and simply
stating it much more simply in terms of wavelength would peg down both
the application and the validity of the claim. Is a tenth wavelength
sufficient to obtain the maximum possible range? How about 10
wavelengths?

The difference between the performance of a tenth wavelength vertical
antenna, and the optimally sized (roughly 5/8ths wavelength) is not
dramatic. Now compare the tenth wavelength vertical to its 10
wavelength distant cousin, and drama unfolds profoundly - subverting
the expectation that larger = maximum range.

73's
Richard Clark, KB7QHC

On Thu, 22 Jan 2009 18:05:03 -0800 (PST), wrote:

On Jan 21, 8:59*pm, Richard Clark wrote:


Hi Mark,

That would seem to indicate you seriously unbalanced the antenna by
the side feed which is geometrically unbalanced. *For instance, the
line doesn't lead off horizontally for any great distance, does it?

Of course, this all hinges on what you mean by not "near as well."

Not sure.. I don't the the position of the feed line should
have been a problem, but it's been so long since I tried it,
I forgot what happened. I just seem to remember trying it
one time, and stuck with the bottom feed.
I'll have to try it again later. I could use my circular 16 inch
dia loop. It's small enough I can easily hold it and shift the
polarization just by rotating it.

Hi Mark,

When you say rotating, do you mean about its axis along the chord of
its diameter, or rotate as in roll about its circumference?

73's
Richard Clark, KB7QHC

wrote:
I don't see how you could be receiving the magnetic
field if say you are 150 miles away from the station.

The same (flawed) argument could be used for the
electric field. :-)

Every photon contains both an electric field and
a magnetic field. The physical particles associated
with all electric, magnetic, and electromagnetic
fields are photons. It is simplistic thinking to
try to separate these phenomena which were unified
a long time ago.

Any receiving antenna is receiving electromagnetic
waves (photons). The ratio of the electric field
to the magnetic field is constant for free space.
A wire antenna in free space responds to the electric
field and extracts power resulting in less power being
available to both electric and magnetic fields. A ferrite
rod antenna responds to the magnetic field and extracts
power resulting in less power being available to both
electric and magnetic fields. The plane wave E-field and
H-field are normal to each other and polarized by
the plane wave transmitting antenna.

The power in an EM wave is ExH and the ratio of E/H
is constant for a constant medium. If energy is
extracted from either the E-field or H-field, the
magnitude of both fields are reduced by the same
percentage.

At the California 75m mobile shootouts that I attended,
the receiving antenna was a horizontal ferrite rod. It
was relatively impervious to the effects of non-metallic
objects in its vicinity, e.g. human bodies. It was
receiving the vertically polarized ground wave at a
distance of about 10WL from the transmitting antenna.

From W8JI web page..
"Acceleration of charges causes a very unique force
on other charges in the Universe. We call this effect
electromagnetic radiation. It is a totally different effect,
and it is independent of induction fields. This is the only
effect or force that works to move charges at a very
large distance, and it cannot be created by mixing
induction fields. "

W8JI doesn't seem to realize that "induction fields" have
been unified into the field of "electromagnetism". Any
difference between an electric field, a magnetic field,
and an electromagnetic field is purely quantitative, not
qualitative as W8JI implies.

I'm not saying that a coaxial loop is a "magnetic" antenna.
I am saying that antennas do exist which respond primarily
to the magnetic field and a ferrite rod antenna is one
obvious example proven by rotating the ferrite rod in the
presence of a vertically polarized signal. Note the
polarization of a radiated plane wave is referenced to
the E-field, not the H-field.
--
73, Cecil http://www.w5dxp.com