loop antennas
 

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?

loop antennas
 

On 6/13/2012 5:11 PM, 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?

None. The only purpose is to ensure balance, which helps give
deeper nulls.

But that is not the only way to ensure balance. A shield is
not required for that function.
None of my AM-BC loops are shielded. I have tried shielded
loops though, just to see for myself if any difference.
There no difference, assuming all of the loops were balanced
and fed properly.
The mythology of loops is a lot like the various myths you
see pertaining to grounds, and grounding. :|
Some claim a shielded loop is "quieter" than an unshielded loop.
I know from testing, that is pure hogwash.
Both are quite capable of picking up noise. After all, noise is
RF just like any other signal, and follows all the same rules.
The true test of a small loop is how deep the nulls are.
If you can make daytime AM ground wave signals disappear by
turning the loop, you are in pretty good shape.
And *any* small loop is capable of that if all is well in the
world.

loop antennas
 

"NM5K" napisal w wiadomosci
...
On 6/13/2012 5:11 PM, 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.

"The operation of the shielded loop is explained popularly by first stating
that the desired loop current is due to the magnetic field, and then
maintaining that the metal shield cannot be penetrated by the electric field
but can be penetrated by the magnetic field. All these arguments are
incorrect in the light of fundamental electromagnetic principles."

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

None. The only purpose is to ensure balance, which helps give
deeper nulls.

But that is not the only way to ensure balance. A shield is
not required for that function.
None of my AM-BC loops are shielded. I have tried shielded
loops though, just to see for myself if any difference.

Do you use them to the "direction finding"?

"The advantage of this feed arrangement is that the coaxial feed typically
enters the loop opposite to the gap, and if attention is paid to symmetry of
the loop and feed, the balance that is achieved. Best balance yields the
deepest null which is important in direction finding applications for
instance."
S*

..

loop antennas
 

On 06/13/2012 06:11 PM, 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..."

Hello, and a loop (dipole) antenna doesn't "respond" to just the
magnetic (electric) component of a propagating electromagnetic wave. A
(receiving) loop or dipole antenna intercepts the incoming
electromagnetic (EM) wave. Last time I checked an EM wave had both
electric and magnetic components. Just because an orientation of an
axis of the antenna resulting in maximum signal strength is parallel to
the electric or magnetic component of an EM wave doesn't mean that it's
responding to just that component.

I wish hams and others would quit trying to redefine electromagnetic
theory. Hams have designed and constructed novel and practical antennas
over the years but their explanations about how they work are often just
plain wrong. Sincerely, and 73s from N4GGO,

--
J. B. Wood e-mail:

loop antennas
 

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

loop antennas
 

"Szczepan Bialek" wrote in message
...


Do you use them to the "direction finding"?

S*
Amateur radio DF on VHF (very popular) tends to use yagis.
Loops seem to be used more for MW and HF DF.


Regards, Ian.

loop antennas
 

"J.B. Wood" napisal w wiadomosci
...
On 06/13/2012 06:11 PM, 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..."

Hello, and a loop (dipole) antenna doesn't "respond" to just the magnetic
(electric) component of a propagating electromagnetic wave. A (receiving)
loop or dipole antenna intercepts the incoming electromagnetic (EM) wave.
Last time I checked an EM wave had both electric and magnetic components.
Just because an orientation of an axis of the antenna resulting in maximum
signal strength is parallel to the electric or magnetic component of an EM
wave doesn't mean that it's responding to just that component.

I wish hams and others would quit trying to redefine electromagnetic
theory. Hams have designed and constructed novel and practical antennas
over the years but their explanations about how they work are often just
plain wrong. Sincerely, and 73s from N4GGO,

The explanations are wrong because the radio waves are simply the electric
waves or the electron waves.
From this point of view the next is obvious;
"Since the directional response of small loop antennas includes a sharp null
in the direction normal to the plane of the loop, they are used in radio
direction finding at longer wavelengths. The loop is thus rotated to find
the direction of the null."

" Although a similar argument may seem to apply to signals received in that
plane, that voltages generated by an impinging radio wave would cancel along
the loop, this is not quite true due to the phase difference between the
arrival of the wave at the near side and far side of the loop."
From: http://en.wikipedia.org/wiki/Loop_antenna
S*

loop antennas
 

On 6/14/2012 3:33 AM, Szczepan Bialek wrote:


But that is not the only way to ensure balance. A shield is
not required for that function.
None of my AM-BC loops are shielded. I have tried shielded
loops though, just to see for myself if any difference.

Do you use them to the "direction finding"?

No. I use them for MW broadcast reception.
I generally don't use them much above the 160m band.
My largest loop covering from longwave to about 2 MHZ,
using switchable caps.

loop antennas
 

On 06/14/2012 12:48 PM, Szczepan Bialek wrote:
"J.B. napisal w wiadomosci
...
On 06/13/2012 06:11 PM, 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..."

Hello, and a loop (dipole) antenna doesn't "respond" to just the magnetic
(electric) component of a propagating electromagnetic wave. A (receiving)
loop or dipole antenna intercepts the incoming electromagnetic (EM) wave.
Last time I checked an EM wave had both electric and magnetic components.
Just because an orientation of an axis of the antenna resulting in maximum
signal strength is parallel to the electric or magnetic component of an EM
wave doesn't mean that it's responding to just that component.

I wish hams and others would quit trying to redefine electromagnetic
theory. Hams have designed and constructed novel and practical antennas
over the years but their explanations about how they work are often just
plain wrong. Sincerely, and 73s from N4GGO,

The explanations are wrong because the radio waves are simply the electric
waves or the electron waves.

Hello, and they are most certainly not "electric" waves. What part of
"electromagnetic" don't you understand? (It's just this kind of stuff
that prompted my previous post) I take it you're not an EE or have ever
taken any undergrad/grad courses in EM theory. In any event someone
else can continue this starting-to-drift off topic thread. Sincerely,

--
J. B. Wood e-mail:

loop antennas
 

On 6/14/2012 12:50 PM, J.B. Wood wrote:
On 06/14/2012 12:48 PM, Szczepan Bialek wrote:
"J.B. napisal w wiadomosci
...
On 06/13/2012 06:11 PM, 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..."

Hello, and a loop (dipole) antenna doesn't "respond" to just the
magnetic
(electric) component of a propagating electromagnetic wave. A
(receiving)
loop or dipole antenna intercepts the incoming electromagnetic (EM)
wave.
Last time I checked an EM wave had both electric and magnetic
components.
Just because an orientation of an axis of the antenna resulting in
maximum
signal strength is parallel to the electric or magnetic component of
an EM
wave doesn't mean that it's responding to just that component.

I wish hams and others would quit trying to redefine electromagnetic
theory. Hams have designed and constructed novel and practical antennas
over the years but their explanations about how they work are often just
plain wrong. Sincerely, and 73s from N4GGO,

The explanations are wrong because the radio waves are simply the
electric
waves or the electron waves.

Hello, and they are most certainly not "electric" waves. What part of
"electromagnetic" don't you understand? (It's just this kind of stuff
that prompted my previous post) I take it you're not an EE or have ever
taken any undergrad/grad courses in EM theory. In any event someone else
can continue this starting-to-drift off topic thread. Sincerely,


He is either an idiot, an ignorant guy that refuses to learn, or a troll.

It doesn't matter all that much actually.

tom
K0TAR