Hello John,

On 2 mar, 18:14, "J.B. Wood" wrote:
On 3/2/2011 8:40 AM, Wimpie wrote:



On 2 mar, 13:58, "J.B. *wrote:
On 02/23/2011 10:00 AM, RadioWaves wrote: *Today I have put my homepage online with information about the Magnetic Loop
Antenna.

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

PA7NR

Hmmm. *A "magnetic" loop antenna. *Must be some other types of loop
antennas as well. *Maybe there are also "electric" loop antennas.

Guess they left something out of all those antenna textbooks I have ;-)
Sincerely, and 73s from N4GGO,

--
J. B. Wood * * * * * * * * *e-mail:

Hello John,

When you cut the loop at two opposite positions, yes, you can make
your "electric" loop.

It will generate lots of E-field, you may need another coil for
matching, and it is probably less efficient then a short straight
dipole with massive capacitive disks to get larger I*delta(le)
product.

Best regards,

Wim
PA3DJS
www.tetech.nl
In case of PM, please remove abc first.

Hello, and the not-so-subtle point is that there aren't magnetic,
electric, or any other such "types" of loop antennas. *There are just
loop antennas that can further be described as shielded/unshielded,
balanced/unbalanced, electrically small or large. *Just like we don't
transmit (propagate) electric (E) or magnetic (H) fields by themselves.

The purpose of an antenna is to radiate and/or intercept an
electromagnetic field. *By definition energy radiated by a transmitting
antenna is not temporarily stored in the antenna's local electric or
magnetic field. *It's been released into free space subject to
interception by a receiving antenna(s) or any other parasitic
structures. *The receiving antenna transfers part the intercepted energy
to the load (receiver and other dissipative losses) and scatters the
rest back into free space.

By contrast, a transformer, for example, is a "magnetic" device that is
intended to transfer energy by a localized means (induction) other than
the propagation/interception of electromagnetic radiation.

If in your opinion there do not exist antennas that generate a
dominant magnetic or electric field (in the near field), then you are
contradicting yourself, as you can't transfer energy with a magnetic
field or electric field only. So your transformer also involves
electric fields. Maybe you should look into the Poynting theorem.

To further confuse the issue, a conductor in the near (reactive) field
of a transmitting antenna will have current induced in it by the
antenna's local electric and/or magnetic fields. *However, that's not
the usual purpose for which we design antennas. *An exception might be
the immoboliser (PATS) system used in late-model motor vehicles that
incorporates a ring antenna embedded in the steering column that is
closely coupled at RF frequencies to the transponder chip and loop
antenna embedded in the vehicle ignition key. *So is it a
transmit-receive antenna configuration or a primary coil-secondary coil
transformer configuration? *Given the proximity of the inserted key to
the steering column I would guess the latter. *Sincerely,

--
J. B. Wood * * * * * * * * *e-mail:

When a noise source is about 5..10m away from an 3.6 MHz antenna, the
coupling of that noise source towards a "magnetic" loop antenna may be
different from the coupling towards an "electric" antenna, though
both antennas may produce the same far field radiation. This is not
from a textbook, but from experience (I am also working in power
electronics).

I fully agree with you on the far field statements, but when you live
in an apartment (where significant spurious emission from home
equipment are in the near field of your 3.6 MHz antenna), a so-called
magnetic loop antenna may behave different (w.r.t. a short "electric"
dipole). It can be worse or better. Many radio amateurs know this from
experiments, without knowing the EM theory behind it.

I have no problems when people talk about a "magnetic loop antenna".
It shows me that they are discussing an antenna with a circumference
0.2 lambda. When people talk about a "loop antenna", it can be
anything.

Best regards,


Wim
PA3DJS
www.tetech.nl