"Szczepan Bialek" wrote in message
...


Hello, and they are most certainly not "electric" waves.

For the all Fathers of the radio they are the electric waves.
You wrote: "Hams have designed and constructed novel and practical
antennas over the years but their explanations about how they work are
often just plain wrong."

Could you give as the correct explanation?
S*

Hello Szczepan.

We've tried to assist you but you seem to prefer to stay with 19th century
knowledge rather than learn modern knowledge. If you ask for help and don't
accept the answers you get then there's not a lot we can do ... other than
disregard your postings and go and operate our radio stations.

You need to get a modern textbook on radio theory. One suitable for amateur
radio should be okay. Have a look at www.rsgb.org.and www.arrl.org

Kindest regards, Ian.

On Friday, June 15, 2012 2:44:39 AM UTC-5, Szczepan Bialek wrote:
Radio waves and light are the oscillatory flow of electrons (L. Lorenz
1869).

Lorenz (and all other physicists and mathematicians) were obviously ignorant of photons in those days. Here is what a more knowledgeable physicist has said more than a century later:

Quoted from: "The Strange Theory of Light and Matter", (c)1985, by Richard P. Feynman

"So now, I present to you the three basic actions, from which all the phenomena of light and electrons arise:

-Action #1: A photon goes from place to place.
-Action #2: An electron goes from place to place.
-Action #3: An electron emits or absorbs a photon."

When Feynman says "light", he is including RF. Photons travel at the speed of light in the medium which is impossible for electrons which possess rest mass. There are no electrons in a pure vacuum, yet light and radio waves pass through it at the speed of light with no problem.

Following your "logic", why go back to 1869? Why not question the periodic table of elements because a few millennia ago, men of science asserted that there are four elements: earth, air, fire, and water. So why not adopt the four element argument as well?
--
73, Cecil, w5dxp.com

El 14-06-12 0:11, garyr escribió:
This site http://www.frontiernet.net/~jadale/Loop.htm states that: "A
properly designed Loop primarily responds to the magnetic component of the
radio wave. Note that noise resides primarily in the electrical
component..."

Whereas this site shows that that is not the case:
http://vk1od.net/antenna/shieldedloop.

So what is the advantage, if any, of a shielded loop antanna?

Consider three receivers:

1) Shielded loop antenna, receiver with differential input (center-tapped
transformer or instrumentation amp). The two ends of the inner conductor
of the antenna connected to the differential inputs and the shield
connected to ground.

2) Same as above but without the shield.

3) Unshielded loop antenna, receiver with single-ended input.
One end of the loop connected to the receiver input and the other to
ground.

Assuming equal gains and bandwidths, would there be any
difference in the sensitivity or noise level at the output of the three
receivers?


I agree with your second link (by VK1OD).

The time varying magnetic field generates an electric field and that
is received by the loop. When you screen it completely, it doesn't
work, you need the gap.

By placing the gap opposite to the feed point, you get a balanced loop
without the need of ferrite or other constructions. If you can get
balance via other means, you don't need the screen. Balancing the
loop reduces noise due to common mode issues. This isn't different
from using a balun between a coaxial cable and a symmetrical dipole.

Your option three may behave competently different, as the coaxial
cable, power supply cable, switch mode power supply, etc may
contribute to reception of signal and noise due to common mode to
differential mode conversion.

From my experience (reception) with electrically small well-balanced
indoor loops and indoor dipoles, I found some advantage of the loop
over the electric dipole at low frequencies (say below 3 MHz). I
contribute this mainly because of the nulling capability. Whether is
applies to your location depends on the field distribution of the
noise at your location.

At higher frequencies there is difference in S/N ratio, but not in
favor of one antenna. Sharp nulling wasn't possible. So to know what
option is best for you, you need to try it. Maybe install both options
and select the antenna that gives best results as this will depend on
frequency and the angle of arrival of the radiation you want to receive.

Other thing that may really help is to find your local source(s) of
noise, use lots of ferrites and try to find a sweet spot for best S/N
ratio.

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

I agree with your second link (by VK1OD).

The time varying magnetic field generates an electric field and that is
received by the loop. When you screen it completely, it doesn't work,
you need the gap.

By placing the gap opposite to the feed point, you get a balanced loop
without the need of ferrite or other constructions. If you can get balance
via other means, you don't need the screen. Balancing the loop reduces
noise due to common mode issues. This isn't different from using a balun
between a coaxial cable and a symmetrical dipole.

Your option three may behave competently different, as the coaxial cable,
power supply cable, switch mode power supply, etc may contribute to
reception of signal and noise due to common mode to differential mode
conversion.

From my experience (reception) with electrically small well-balanced
indoor loops and indoor dipoles, I found some advantage of the loop over
the electric dipole at low frequencies (say below 3 MHz). I contribute
this mainly because of the nulling capability. Whether is applies to your
location depends on the field distribution of the noise at your location.

At higher frequencies there is difference in S/N ratio, but not in favor
of one antenna. Sharp nulling wasn't possible. So to know what option is
best for you, you need to try it. Maybe install both options and select
the antenna that gives best results as this will depend on frequency and
the angle of arrival of the radiation you want to receive.

Other thing that may really help is to find your local source(s) of noise,
use lots of ferrites and try to find a sweet spot for best S/N ratio.

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

So you are saying that cases 1 & 2 above are essentially equvalent if the
loops are balanced. In terms of noise rejection, there is no analogy to be
drawn between a shielded loop and a shielded cable.

El 15-06-12 16:09, garyr escribió:
I agree with your second link (by VK1OD).

The time varying magnetic field generates an electric field and that is
received by the loop. When you screen it completely, it doesn't work,
you need the gap.

By placing the gap opposite to the feed point, you get a balanced loop
without the need of ferrite or other constructions. If you can get balance
via other means, you don't need the screen. Balancing the loop reduces
noise due to common mode issues. This isn't different from using a balun
between a coaxial cable and a symmetrical dipole.

Your option three may behave competently different, as the coaxial cable,
power supply cable, switch mode power supply, etc may contribute to
reception of signal and noise due to common mode to differential mode
conversion.

From my experience (reception) with electrically small well-balanced
indoor loops and indoor dipoles, I found some advantage of the loop over
the electric dipole at low frequencies (say below 3 MHz). I contribute
this mainly because of the nulling capability. Whether is applies to your
location depends on the field distribution of the noise at your location.

At higher frequencies there is difference in S/N ratio, but not in favor
of one antenna. Sharp nulling wasn't possible. So to know what option is
best for you, you need to try it. Maybe install both options and select
the antenna that gives best results as this will depend on frequency and
the angle of arrival of the radiation you want to receive.

Other thing that may really help is to find your local source(s) of noise,
use lots of ferrites and try to find a sweet spot for best S/N ratio.

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

So you are saying that cases 1& 2 above are essentially equvalent if the
loops are balanced. In terms of noise rejection, there is no analogy to be
drawn between a shielded loop and a shielded cable.





Hello Gary,

You are right, it is what I am saying.

There is no analogy between the shielding function of the braid in a
coaxial transmission line and the shield in your loop.

For the "shielded" loop, the received voltage is across the gap in the
shield. The shield is the actual single turn loop. The inner
conductor is just there to transport the received signal to the
opposite side of the gap where you can go down (with coaxial cable) to
your receiver, maintaining balance.

Theoretically a coaxial transmission line system is completely closed.
Water from the outside can't reach the inner conductor, source or
load. When cutting a gap in the screen, the coaxial transmission line
system will leak.

Shielded loop with more turns
If you run more turns within the shield of the loop, you pass the gap
many times. When you pass it 3 times, you will get three times the
voltage, hence the impedance and loop inductance increase.

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

"Wimpie" wrote in message
el.net...
El 15-06-12 16:09, garyr escribió:
I agree with your second link (by VK1OD).

The time varying magnetic field generates an electric field and that is
received by the loop. When you screen it completely, it doesn't work,
you need the gap.

By placing the gap opposite to the feed point, you get a balanced loop
without the need of ferrite or other constructions. If you can get
balance
via other means, you don't need the screen. Balancing the loop reduces
noise due to common mode issues. This isn't different from using a balun
between a coaxial cable and a symmetrical dipole.

Your option three may behave competently different, as the coaxial
cable,
power supply cable, switch mode power supply, etc may contribute to
reception of signal and noise due to common mode to differential mode
conversion.

From my experience (reception) with electrically small well-balanced
indoor loops and indoor dipoles, I found some advantage of the loop over
the electric dipole at low frequencies (say below 3 MHz). I contribute
this mainly because of the nulling capability. Whether is applies to
your
location depends on the field distribution of the noise at your
location.

At higher frequencies there is difference in S/N ratio, but not in favor
of one antenna. Sharp nulling wasn't possible. So to know what option
is
best for you, you need to try it. Maybe install both options and select
the antenna that gives best results as this will depend on frequency and
the angle of arrival of the radiation you want to receive.

Other thing that may really help is to find your local source(s) of
noise,
use lots of ferrites and try to find a sweet spot for best S/N ratio.

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

So you are saying that cases 1& 2 above are essentially equvalent if the
loops are balanced. In terms of noise rejection, there is no analogy to
be
drawn between a shielded loop and a shielded cable.





Hello Gary,

You are right, it is what I am saying.

There is no analogy between the shielding function of the braid in a
coaxial transmission line and the shield in your loop.

For the "shielded" loop, the received voltage is across the gap in the
shield. The shield is the actual single turn loop. The inner conductor is
just there to transport the received signal to the opposite side of the
gap where you can go down (with coaxial cable) to your receiver,
maintaining balance.

Theoretically a coaxial transmission line system is completely closed.
Water from the outside can't reach the inner conductor, source or load.
When cutting a gap in the screen, the coaxial transmission line system
will leak.

Shielded loop with more turns
If you run more turns within the shield of the loop, you pass the gap many
times. When you pass it 3 times, you will get three times the voltage,
hence the impedance and loop inductance increase.

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

Wim,

Thanks very much for your lucid explanation of how shielded loops function.
I've been using one with a receiver I made to monitor VLF signals. It works
quite well and I had thought it was because of all the local noise I was
avoiding. But then I stumbled across VK1OD's article...

Best regards,
Gary Richardson, AA7VM

PS
Thanks also to all the other respondents. This has been a very interesting
thread.

On 06/14/2012 08:12 AM, Wimpie wrote:


The time varying magnetic field generates an electric field and that is
received by the loop. When you screen it completely, it doesn't work,
you need the gap.


Hello, and one more (and final) time: Electric and magnetic fields by
themselves don't propagate, only electromagnetic fields (EM) can
transport energy over vast distances. A transmitting antenna has LOCAL
(near) electric and magnetic fields but what propagates (i.e. what a
receiving antenna sees as the far-field) is an EM field. A receiving
antenna has an "effective area" that captures energy in the incident EM
wave; what isn't dissipated in the load at the receiving antenna
terminals is reflected (scattered) by the antenna (after allowing for
any dissipative/ohmic losses in the antenna structure).

As economics professor Peter Morici would say "It isn't all that
complicated." (But the devil's in the details). Sincerely and 73s from
N4GGO,


--
J. B. Wood e-mail:

On Tuesday, June 19, 2012 5:35:57 AM UTC-5, J.B. Wood wrote:
As economics professor Peter Morici would say "It isn't all that
complicated."

What a small shielded loop responds to should be easy to demonstrate. We know that a florescent light bulb responds mainly to the electric field because it gets brighter as one moves it from the feedpoint to the top of a mobile antenna. The standing wave voltage loop is at the top of a resonant mobile antenna. The standing wave current loop is at the feedpoint of a resonant mobile antenna.

So simply take the small shielded loop and see where it responds the best up and down a mobile antenna. If some people are correct about it responding mainly to the magnetic field, the measured field strength will be highest at the base of the mobile antenna where the standing wave current is the highest.
--
73, Cecil, w5dxp.com

On 06/19/2012 11:21 AM, W5DXP wrote:
On Tuesday, June 19, 2012 5:35:57 AM UTC-5, J.B. Wood wrote:
As economics professor Peter Morici would say "It isn't all that
complicated."

What a small shielded loop responds to should be easy to demonstrate. We know that a florescent light bulb responds mainly to the electric field because it gets brighter as one moves it from the feedpoint to the top of a mobile antenna. The standing wave voltage loop is at the top of a resonant mobile antenna. The standing wave current loop is at the feedpoint of a resonant mobile antenna.

So simply take the small shielded loop and see where it responds the best up and down a mobile antenna. If some people are correct about it responding mainly to the magnetic field, the measured field strength will be highest at the base of the mobile antenna where the standing wave current is the highest.
--
73, Cecil, w5dxp.com

Hello, and one has to make the distinction of whether the receiving loop
is in the near or far field with respect to the source of the incident
energy. A quick test is to note whether shorting or open-circuiting the
terminals of the loop (or any receiving antenna for that matter) has any
effect on the current flowing into the terminals of the source
(transmitting) antenna. If there's no effect then the receiving antenna
is most likely decoupled inductively (magnetically) and capacitively
(electrically) from the transmitting antenna. What is seen as available
power at the receiving antenna in that case is due to its interception
of a propagating EM field. The fact that the orientation of an axis of
the antenna aligns with the E or H component of an incident EM field is
just a result of the applicable electrophysics. Sincerely,

--
J. B. Wood e-mail:

On Wed, 13 Jun 2012 15:11:06 -0700, "garyr" wrote:

This site http://www.frontiernet.net/~jadale/Loop.htm states that: "A
properly designed Loop primarily responds to the magnetic component of the
radio wave. Note that noise resides primarily in the electrical
component..."

Whereas this site shows that that is not the case:
http://vk1od.net/antenna/shieldedloop.

So what is the advantage, if any, of a shielded loop antanna?

Consider three receivers:

1) Shielded loop antenna, receiver with differential input (center-tapped
transformer or instrumentation amp). The two ends of the inner conductor
of the antenna connected to the differential inputs and the shield
connected to ground.

2) Same as above but without the shield.

3) Unshielded loop antenna, receiver with single-ended input.
One end of the loop connected to the receiver input and the other to
ground.

Assuming equal gains and bandwidths, would there be any
difference in the sensitivity or noise level at the output of the three
receivers?

A loop is a loop is a loop, meaning that one side conductor goes
upwards while the other side goes downwards in contrast to a
linear wire antenna or a dipole which is extending in one direction
only. The up-and down (left and right) parts of the wire cancel out
each other at least partially when collecting energy from an electric
field, while the energy uptake from a magnetic field is proportional
to the loop area.
This electric noise cancellation is not perfect, due to unsymmetries
in the field, therefore it pays to shield the loop wires and decrease
the electric influences further.

I hope my explanation is simple enough.

w.