On Fri, 23 Jan 2009 17:06:24 -0600, (Richard
Harrison) wrote:

Jim Kelley, AC6XG wrote:
"Scientists at the MIT Radiation Labs during World War ll found that it
was a simple matter to measure E and H individually."

Yes indeed. Two dircuits in separate shielded enclosures can be coupled
with a coupling capacitor and only the E-field gets through. Similarly,
two transformer windings separated by a Faraday shield are completely
coupled magnetically and have no electrostatic coupling. I`ve worked in
several broadcast stations and all towers were so coupled to avoid
capacitive coupling which could give advantage to harmonic frequencies
over the broadcast fundamental frequency.

Yes indeed. Two examples of rare species that require a controlled
environment to persist.

However, neither describe how you can build an antenna that can boost
its S/N ratio by virtue of ignoring one field over the other - unless
Art has a 160M (AM Band much less) waveguide invention that occupies
the volume of a container of Quaker Oats.

Let's for the moment squeeze our eyes real tight and imagine that it
has come to pass and here comes the noise and the signal (of that
eponymous S/N ratio fame). They both impinge upon this "state of the
Art" design. Which field is chosen won't matter much (but I can
imagine this will be argued until the design is deaf to both).

73's
Richard Clark, KB7QHC

Richard Clark, KB7QHC wrote:
"Which field is chosen won`t mstter much----."

Agreed as the fields trade the same energy back and forth on each cycle.

Narrowing bandwidth is not the only way to reduce noise. Auto radios use
non-directional antennas out of convenience. A desired signal can come
from any direction. But, directivity can improve signal to noise ratio
as it reduces noise from unwanted directions. An example is my
Telefunken receiver which features a large horizontal ferrite rod
antenna. This rod is rotatable in azimuth from a control on the front
panel for best reception. This radio was designed for reception in a
fixed location so azimuth change is needed only when changing stations.
A ferrite rod antenna can be used anywhere to improve s/n ratio through
its high directivity. It requires more inconvenience to reset when the
direction of the vehicle changes and it needs to be mounted outside the
shielded enclosure and equipped with a direction control, i.e. a
rotator.

MFJ among others sells such a ferrite rod antenna for the standard
broadcast band. Aimed for best reception of KGO in San Francisco, it
would discriminate against noise from most other directions.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
MFJ among others sells such a ferrite rod antenna for the standard
broadcast band.

Richard, what's the MFJ part number? I can't locate it
in the catalog.
--
73, Cecil http://www.w5dxp.com

Cecil wrote:
"Richard, what`s the MFJ part number?"
Not sure as I don`t have a catalog but searched on "MFJ ferrite loop
antenna" which yielded several responses including books, web sites, and
a Radio Nederland 'build your own loop" instruction page, several of
these mentioned MFJ 261 if my memory is correct. these responses assured
me there was at least one MFJ ferrite loopstick offered before I posted.
The right old radio would probably yield both variable capacitor and
loopstick for a portable directional BCB antenna.

Best regards, Richard Harrison, KB5WZI

I searched again on MFJ BCB ferrite loop antenna. The number immediately
appeared and was 1026 so my memory must have been wrong. It was not 261.

Best regards, Richard Harrison, KB5WZI