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 high
building picks up electro smog over the full length from the floors
underneath, the loop covers a
small space and is physically further away from most 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, 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
quickly and the larger bandwidth (lower Q) makes it easier to hear stations
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 if 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 have information about the formula.

Best 73's

Norbert, PA7NR