On Wed, 23 Feb 2011 16:00:57 +0100, "RadioWaves" radio@oidar wrote:

Today I have put my homepage online with information about the Magnetic Loop
Antenna.

http://www.qsl.net/pa7nr/

PA7NR

Hi OM,

I especially like your coverage of your antenna from I3VHF.

On your second page, unfortunately, you have some misconceptions about
loop antennas.

All antennas exhibit the same noise characteristics. If you erected
a conventional (electric) dipole in the same space, it would exhibit
the same characteristics.

It is quite curious how you describe a front/back ratio for a dipole
(the loop is a magnetic dipole, and as such "should" show a
conventional dipole pattern).

As for loop efficiency, you state:
"When a magnetic loop antenna is used for
3.5 MHz with a perimeter of 4 meter (13.3 foot) ,
it has an efficiency of approximately 3%."
Please show the math.

73's
Richard Clark, KB7QHC

Hi Richard,

Thank you for your reply and your interest in my homepage. I will answer
your questions between the lines.

I will use the remarks that I get to improve the content of the article on
my site.

Hi OM,

I especially like your coverage of your antenna from I3VHF.

On your second page, unfortunately, you have some misconceptions about
loop antennas.

All antennas exhibit the same noise characteristics. If you erected
a conventional (electric) dipole in the same space, it would exhibit
the same characteristics.


I agree that they are electrically equivalents. However, my point is that
the magnetic loop has useful benefits over the dipole antenna for RX under
certain circumstances. I believe the magnetic loop construction will in many
cases deliver an acceptable signal at the receiver with less disturbances
such as atmospheric noise.

About external noise sources:

The loop is smaller (less surface) and therefore picks up less static noise.
The dipole covers a larger area in which there can be sources of noise.

The pickup loop that connects the coax to the loop antenna is isolated from
the antenna and it forms a shortcut for DC. The signal transfer is
inductive.

The magnetic loop tunes to the frequency and there is no external antenna
tuner needed.

About intenal receiver noise and mix-products:

The magnetic loop in itself is a band pass filter at the source of the
receiving signal. It eliminates strong signals outside the received
frequency. Therefore the receiver can receive the wanted signals with
maximum sensitivity. The band pass functionality of the loop protects the
radio from overloading. And as a result of that the radio will be quiet and
doesn't need to pick a weak signal from an overloaded band. The bandwidth of
the I3VHF is very small in the 40 m band. AM modulation is not possible as
the bandwidth of the loop is too small here for passing a standard AM
signal. The signal will be clipped and the transceiver react to that which
can be seen on the SWR meter. SWR starts to alternate on the rhythm of the
modulation. The bandwidth of the antenna gets larger in the higher bands. I
believe that in the 40 meter band the I3VHF only lets trough one frequency
in SSB. The receiver is almost mute tuning higher or lower.

As for receiving the readability is more important than signal strength. The
lower RX signal from the magnetic loop is often more readable than when
using a full size dipole at ideal height. I think that the advantages are
best in the Low bands, e.g. 80, 40, 30 meter.

For TX there are advantages of the magnetic loop over the full size dipole.
When one has shortage of space. The high small band pass filter that the
Magnetic Loop is, makes the radiated signal free of harmonics. Therefore
there is a smaller chance of rfi to be expected .

Maybe some of the points here are not based on solid scientific research.
But it is what I found doing experiments with the loops.

It is quite curious how you describe a front/back ratio for a dipole
(the loop is a magnetic dipole, and as such "should" show a
conventional dipole pattern).


The data is based on the specifications of the manufacturer of the I3VHF
loop antenna.

http://www.ciromazzoni.com/English/L...oop%20Baby.htm

In the manual, page 42, 43 there is a picture of the radiation pattern:

http://www.ciromazzoni.com/English/L...nna/Manual.pdf

It also surprised me as I expected a dipole pattern.

As for loop efficiency, you state:
"When a magnetic loop antenna is used for
3.5 MHz with a perimeter of 4 meter (13.3 foot) ,
it has an efficiency of approximately 3%."
Please show the math.

The 3 % efficiency is hypothetical based on the outcome of calculations
software that is available on the Internet.

For example the loop calculation software of G4FGQ.


73's
Richard Clark, KB7QHC

Best Regards,

Norbert , PA7NR

On Wed, 23 Feb 2011 21:53:00 +0100, "RadioWave" radio@oidar wrote:

Hi Richard,

Thank you for your reply and your interest in my homepage. I will answer
your questions between the lines.

I will do the same.

I will use the remarks that I get to improve the content of the article on
my site.

Hi OM,

I especially like your coverage of your antenna from I3VHF.

On your second page, unfortunately, you have some misconceptions about
loop antennas.

All antennas exhibit the same noise characteristics. If you erected
a conventional (electric) dipole in the same space, it would exhibit
the same characteristics.


I agree that they are electrically equivalents. However, my point is that
the magnetic loop has useful benefits over the dipole antenna for RX under
certain circumstances. I believe the magnetic loop construction will in many
cases deliver an acceptable signal at the receiver with less disturbances
such as atmospheric noise.

Hi Norbert,

Demonstrable proof shows otherwise.

About external noise sources:

The loop is smaller (less surface) and therefore picks up less static noise.

Static is indistinguishable from the RF you want to hear. In other
words static is RF, signals are RF. If your small loop picks up less
of one, it picks up less of both. However, this "picks up less" is
arguable.

The dipole covers a larger area in which there can be sources of noise.

Reread my statement: "If you erected a conventional (electric) dipole
IN THE SAME SPACE."

The pickup loop that connects the coax to the loop antenna is isolated from
the antenna and it forms a shortcut for DC. The signal transfer is
inductive.

This is a tautology, not a reason.

The magnetic loop tunes to the frequency and there is no external antenna
tuner needed.

Here, the Q of the tuned loop DOES contribute to less interference of
out-of-band signals. It does not reduce interference to in-band
signals. Noise is not specific to frequency, although single
frequency emitters can be called noise (unwanted).

About intenal receiver noise and mix-products:

The magnetic loop in itself is a band pass filter at the source of the
receiving signal. It eliminates strong signals outside the received
frequency. Therefore the receiver can receive the wanted signals with
maximum sensitivity. The band pass functionality of the loop protects the
radio from overloading. And as a result of that the radio will be quiet and
doesn't need to pick a weak signal from an overloaded band. The bandwidth of
the I3VHF is very small in the 40 m band. AM modulation is not possible as
the bandwidth of the loop is too small here for passing a standard AM
signal. The signal will be clipped and the transceiver react to that which
can be seen on the SWR meter. SWR starts to alternate on the rhythm of the
modulation. The bandwidth of the antenna gets larger in the higher bands. I
believe that in the 40 meter band the I3VHF only lets trough one frequency
in SSB. The receiver is almost mute tuning higher or lower.

Barring problems of lacking a choke on your control line introducing
SWR issues, I would tend to agree.

As for receiving the readability is more important than signal strength. The
lower RX signal from the magnetic loop is often more readable than when
using a full size dipole at ideal height. I think that the advantages are
best in the Low bands, e.g. 80, 40, 30 meter.

You have a lower signal because you have a lower antenna. Let's not
turn a deficit into a glowing recommendation - especially when you go
to transmit you lose that same gain from low height.

For TX there are advantages of the magnetic loop over the full size dipole.
When one has shortage of space. The high small band pass filter that the
Magnetic Loop is, makes the radiated signal free of harmonics. Therefore
there is a smaller chance of rfi to be expected .

A small (electric) dipole is identical in characteristics. It simply
doesn't come built with its own tuning mechanism.

Your arguments are not about antenna, but tuning.

Maybe some of the points here are not based on solid scientific research.
But it is what I found doing experiments with the loops.

It is quite curious how you describe a front/back ratio for a dipole
(the loop is a magnetic dipole, and as such "should" show a
conventional dipole pattern).


The data is based on the specifications of the manufacturer of the I3VHF
loop antenna.

http://www.ciromazzoni.com/English/L...oop%20Baby.htm

First thing I noticed was the loop on a tower.

In the manual, page 42, 43 there is a picture of the radiation pattern:

http://www.ciromazzoni.com/English/L...nna/Manual.pdf

It also surprised me as I expected a dipole pattern.

As for loop efficiency, you state:
"When a magnetic loop antenna is used for
3.5 MHz with a perimeter of 4 meter (13.3 foot) ,
it has an efficiency of approximately 3%."
Please show the math.

The 3 % efficiency is hypothetical based on the outcome of calculations
software that is available on the Internet.

I presume this is for the MIDI loop with a 2M diameter. The claim
offered is that it exhibits a Q of 1500 at 3.5MHz. The radiation
resistance for that size of loop is 0.49 Ohm. So, if 3% of the power
goes to 0.49 Ohm, then 97% of the power must go to heating up the
large tubular structure's Ohmic resistance (which would be very high,
and quite remarkable for that mass). Let's consider that you took an
Ohmmeter and measured half an Ohm in the structure, then you would be
losing only 50%, not 97%.

If you short your Ohmmeter leads together, I bet they have less than
half an Ohm resistance, why should this massive structure have more
loss than simple wire?

The argument would also have to answer the high Q (that much loss is
very low Q).

For example the loop calculation software of G4FGQ.

Give us the entry data and the formula.

73's
Richard Clark, KB7QHC

On Feb 23, 7:17*pm, Richard Clark wrote:
Static is indistinguishable from the RF you want to hear.

EM wave static is indistinguishable from RF waves. Pstatic, for
instance, is not caused by EM waves and is therefore, distinguishable.
--
73, Cecil, w5dxp.com

All antennas exhibit the same noise characteristics. If you erected
a conventional (electric) dipole in the same space, it would exhibit
the same characteristics.


I agree that they are electrically equivalents. However, my point is that
the magnetic loop has useful benefits over the dipole antenna for RX under
certain circumstances. I believe the magnetic loop construction will in
many
cases deliver an acceptable signal at the receiver with less disturbances
such as atmospheric noise.
Demonstrable proof shows otherwise.


Where can I read about the proof?


About external noise sources:

The loop is smaller (less surface) and therefore picks up less static
noise.

Static is indistinguishable from the RF you want to hear. In other
words static is RF, signals are RF. If your small loop picks up less
of one, it picks up less of both. However, this "picks up less" is
arguable.


Precipitation Static (p-static) can be different.


The dipole covers a larger area in which there can be sources of noise.

Reread my statement: "If you erected a conventional (electric) dipole
IN THE SAME SPACE."


In a practical situation, for instance a 20 meter long dipole over a
building picks up electro smog from the floors underneath, the loop covers a
small space and is physically further away from part of the sources.


In free space high in the sky they will pick up the same noise, I
agree.


The magnetic loop tunes to the frequency and there is no external antenna
tuner needed.

Here, the Q of the tuned loop DOES contribute to less interference of
out-of-band signals. It does not reduce interference to in-band
signals. Noise is not specific to frequency, although single
frequency emitters can be called noise (unwanted).




The bandwidth is so narrow in the 40 meter band (I3VHF) that only a few kHz
so there is a smaller chance of strong out
of band signals.

By the way, having to tune the loop every time when changing frequency is a
mayor disadvantage of tuned magnetic loops. The MFJ loop can be tuned rather
fast and the larger bandwidth makes it easier to hear within several kHz
from the tuned frequency.


As for receiving the readability is more important than signal strength.
The
lower RX signal from the magnetic loop is often more readable than when
using a full size dipole at ideal height. I think that the advantages are
best in the Low bands, e.g. 80, 40, 30 meter.

You have a lower signal because you have a lower antenna. Let's not
turn a deficit into a glowing recommendation - especially when you go
to transmit you lose that same gain from low height.


I don't think that it's just a matter of height. But maybe you are right. I
can't put up a full size verticale on my balcony to compare.

A magnetic loop will work indoor and outdoor. Low on the ground and high in
the sky. And without a counterpoise. Dipoles require space. Verticals
require counterpoise. When there is little space or other restrictions the
loop is a nice alternative.

For transmitting a magnetic loop can be also interesting when there is no
space for a full size antenna.

One could also for example use the full size antenna for TX and the magnetic
loop as an
alternative for RX.

It's not that I'm against dipoles because I reviewed some magnetic loops. I
appreciate the concept of the magnetic loop. I would use a dipole with open
feeding line and symetric tuner where possible.

For TX there are advantages of the magnetic loop over the full size
dipole.
When one has shortage of space. The high small band pass filter that the
Magnetic Loop is, makes the radiated signal free of harmonics. Therefore
there is a smaller chance of rfi to be expected .

A small (electric) dipole is identical in characteristics. It simply
doesn't come built with its own tuning mechanism.

Your arguments are not about antenna, but tuning.


To me the antenna start at the Antenna connector of the tranceiver.



As for loop efficiency, you state:
"When a magnetic loop antenna is used for
3.5 MHz with a perimeter of 4 meter (13.3 foot) ,
it has an efficiency of approximately 3%."
Please show the math.

The 3 % efficiency is hypothetical based on the outcome of calculations
software that is available on the Internet.

I presume this is for the MIDI loop with a 2M diameter. The claim
offered is that it exhibits a Q of 1500 at 3.5MHz. The radiation
resistance for that size of loop is 0.49 Ohm. So, if 3% of the power
goes to 0.49 Ohm, then 97% of the power must go to heating up the
large tubular structure's Ohmic resistance (which would be very high,
and quite remarkable for that mass). Let's consider that you took an
Ohmmeter and measured half an Ohm in the structure, then you would be
losing only 50%, not 97%.


If you short your Ohmmeter leads together, I bet they have less than
half an Ohm resistance, why should this massive structure have more
loss than simple wire?

The argument would also have to answer the high Q (that much loss is
very low Q).




Maybe you can ask the manufacturer and post his explanation here.



For example the loop calculation software of G4FGQ.

Give us the entry data and the formula.




You can download the loop calculation software and enter the dimensions of
the loop. I don't provide software.
I don't know the formula.



73's

Norbert, PA7NR

"RadioWave" radio@oidar wrote
...

A magnetic loop will work indoor and outdoor. Low on the ground and high
in
the sky. And without a counterpoise. Dipoles require space. Verticals
require counterpoise. When there is little space or other restrictions the
loop is a nice alternative.

Your loop is not magnetic. Look at Fig. 2:
http://www.antiquewireless.org/otb/lodge1102.htm

Radio wavesare are radiated from the nodes. In dipole the nodes are created
by reflected wave (waves in the opposite direction). In the loop the waves
travel in oppsite direction and create the nodes also.

Verticals work like the Kundt's tube. Dipoles like the two Kundt's tubes.
A loop is like a dipole where the reflected wave is replacesd by the on from
the second wire.

Hertz has the dipole and the loop:
http://people.seas.harvard.edu/~jone...ertz/S_p11.gif

S*

On Feb 25, 9:11*am, "Szczepan Bialek" wrote:
*"RadioWave" radio@oidar . ..



A magnetic loop will work indoor and outdoor. Low on the ground and high
in
the sky. And without a counterpoise. Dipoles require space. Verticals
require counterpoise. When there is little space or other restrictions the
loop is a nice alternative.

Your loop is not magnetic. Look at Fig. 2:http://www.antiquewireless.org/otb/lodge1102.htm

Radio wavesare are radiated from the nodes. In dipole the nodes are created
by reflected wave (waves in the opposite direction). In the loop the waves
travel in oppsite direction and create the nodes also.

Verticals work like the Kundt's tube. Dipoles like the two Kundt's tubes.
A loop is like a dipole where the reflected wave is replacesd by the on from
the second wire.

Hertz has the dipole and the loop:http://people.seas.harvard.edu/~jone...res/lecture6/h...

S*



don't bother arguing with him, he is stuck in about 1880 with jumping
electrons and a charged aether.

On Feb 25, 6:04*am, K1TTT wrote:
he is stuck in about 1880 with ... a charged aether.

If there is no charged aether, where does the "quantized field in a
vacuum" come from? From Wikipedia: "In quantum field theory, the
Casimir effect and the Casimir-Polder force are physical forces
arising from a quantized field. The typical example is of two
uncharged metallic plates in a vacuum, ..."
--
73, Cecil, w5dxp.com

On Feb 25, 3:11*am, "Szczepan Bialek" wrote:
Radio wavesare are radiated from the nodes. In dipole the nodes are created
by reflected wave (waves in the opposite direction). In the loop the waves
travel in oppsite direction and create the nodes also.

In a dipole, the reflections are naturally from the impedance
discontinuity at the open ends of the dipole. In a loop, the
reflections on the antenna are from the impedance discontinuity at the
feedpoint.
--
73, Cecil, w5dxp.com

"Cecil Moore" napisal w wiadomosci
...
On Feb 25, 3:11 am, "Szczepan Bialek" wrote:
Radio wavesare are radiated from the nodes. In dipole the nodes are
created
by reflected wave (waves in the opposite direction). In the loop the waves
travel in oppsite direction and create the nodes also.

In a dipole, the reflections are naturally from the impedance
discontinuity at the open ends of the dipole. In a loop, the
reflections on the antenna are from the impedance discontinuity at the
feedpoint.

I do not understand. A loop can be made of wires without any discontinuity
at the feedpoint. Pulses send from supply must collide in the loop. The
nodes appear like in a dipole but without reflections. For what you need
reflections in a loop?
S*