On Thu, 24 Feb 2011 20:17:33 +0100, "RadioWave" radio@oidar wrote:

Demonstrable proof shows otherwise.


Where can I read about the proof?

Hi Norbert,

Usually in the first chapter of any college text on antennas.

Precipitation Static (p-static) can be different.

An electrical discharge that is harmonic rich still qualifies as RF.
That pulse electric discharge is going to create a pulse magnetic
field. Guess what? A magnetic antenna (as a loop is often described)
will pick up that field as readily as an electric antenna.

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.

These are operational characteristics of a tuned loop. Look at your
own subject heading: Magnetic Loop - not the same thing.

In fact, the term Magnetic Loop is an invented term. RF is both
magnetic and electric simultaneously. All antennas respond to both.
Your tuned loop exhibits astronomically high electric potentials.
Would you care to guess how high the potentials are for receive as
compared to the field potential it experiences?

Let's put some fantastical numbers to this last question. A reception
field of 1V/M will exhibit ______ V on the capacitive elements of a
resonant tuned loop with a Q of 1500.

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.

A 2 meter wide dipole occupies less space than a 2 meter wide loop.
Once the dipole is matched, performance will be identical.

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

You could as easily say the same for a full size loop. Do you notice
any irony?

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

Why?

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

Then a lot has been unsaid for a tuner to any dipole.

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.

Actually, you need to do this yourself as these are all your choices.
This is your offered explanation and your offered testimony. In fact,
in this, a technical forum, there is every expectation that you could
reasonably perform these technical matters and respond with results.
Do you have an Ohmmeter? Are you proficient in its use?

If you cannot on your own, and without prompting, reconcile 3%
efficiency with a Q of 1500, then you shouldn't be offering technical
advice about Q or efficiency.

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.

I have corresponded with G4FGQ the software designer for YEARS.
Consult the archives. I understand how it works. The question was
for you to write what YOU did, and not what someone else might do.

73's
Richard Clark, KB7QHC