improve S/N for AM car radio by a factor of 2...5...10?
 

christofire wrote:
Could I suggest taking a look at one of the well regarded text books such as
'Antennas' by J. Kraus.

The international 3rd edition is available at www.abebooks.com
for about $22. There's no reason for any amateur radio operator
who is serious about antennas not to have one.

http://www.abebooks.com/servlet/Sear...ions&x=47&y=13
--
73, Cecil http://www.w5dxp.com

improve S/N for AM car radio by a factor of 2...5...10?
 

wrote:
Well, that's my whole point. If the station you are listening to
is 150 miles away, I don't see how the local fields will really
come into play.

One is not receiving the local fields. One is receiving
the radiated EM field consisting of photons traveling at
the speed of light. One has a choice of extracting energy
from the E-field thus creating a voltage which results in
a current or extracting energy from the H-field thus creating
a current which results in a voltage. Given the same load,
the effects of either type of extraction are the same.
--
73, Cecil http://www.w5dxp.com

improve S/N for AM car radio by a factor of 2...5...10?
 

christofire wrote:

I'm aware of issues involved in claiming generation of separate E or H
fields, as has been described by Kabbary et al in their 'crossed-field
antenna', but surely the issues concerning a receiving antenna are
different?

Those issues, and an acute sensitivity to them, are evidently at the
root of the misunderstanding here. The oversensitivity perhaps caused
confusion, irritation, defensiveness, and temporary blurry vision.

Scientists at the MIT Radiation labs during World War II found that it
was a simple matter to measure E and H individually. I imagine that it
is still possible to do without having to perform the miracle of 'field
separation'.

ac6xg

improve S/N for AM car radio by a factor of 2...5...10?
 

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.

Best regards, Richaqrd Harrison, KB5WZI

improve S/N for AM car radio by a factor of 2...5...10?
 

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

improve S/N for AM car radio by a factor of 2...5...10?
 

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

improve S/N for AM car radio by a factor of 2...5...10?
 

On Jan 23, 7:37*am, Cecil Moore wrote:

I'm not saying that a coaxial loop is a "magnetic" antenna.
I am saying that antennas do exist which respond primarily
to the magnetic field and a ferrite rod antenna is one
obvious example proven by rotating the ferrite rod in the
presence of a vertically polarized signal. Note the
polarization of a radiated plane wave is referenced to
the E-field, not the H-field.
--
73, Cecil *http://www.w5dxp.com

I had to ponder the loop for a while. Something kept
bugging me, and it was mainly wondering about the
pattern of say a small 1/10 wave loop, vs a large 1 wave
loop. Both are diamonds.
I was pretty sure I remembered them as having a
different pattern, and I decided to model them to
see.
Well. I found out that even when I'm feeding the
small diamond at the bottom corner, I'm still
getting mostly all vertical polarization.
So with the small vertical loop, I'm getting almost
all vertical polarization, no matter where it is fed.
With it fed on a side corner, which most would
consider vertically fed, I have almost the same
pattern, except it's even cleaner, with very little
horizontal.
Totally unlike the large loop which if I feed at the
bottom, it's almost all horizontally polarized.
So it seems my MW loops are still pretty
much vertically polarized, even when fed at
the bottom corner.
So anyway, as far as the small loops, I'm
not receiving cross polarized after all.
I generally don't see much difference in operation
between a ferrite loop antenna, and a wound
solenoid loop with many turns for MW.
And I did make a "PVC Tube" solenoid loop
antenna once when I was messing around
with them. But don't have it together now.
But I seem to remember it acting basically
the same as all the other versions.
IE: the directivity was off it's ends.
I'd have to make another one to compare
tilting it vertical, vs horizontal.

improve S/N for AM car radio by a factor of 2...5...10?
 

wrote:
I'd have to make another one to compare
tilting it vertical, vs horizontal.

Again, I'm not talking about any loop in air. I'm only
one example of a ferrite rod loop antenna as exists in
AM radios. Those rods are mounted horizontal within the
radio while the polarization of the transmitted signal
is vertical.

This was in response to the assertion that magnetic
field antennas don't exist. A ferrite rod responds to
the EM magnetic field whether there are any coils of
wire on it or not.
--
73, Cecil http://www.w5dxp.com

improve S/N for AM car radio by a factor of 2...5...10?
 

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

improve S/N for AM car radio by a factor of 2...5...10?
 

On Jan 25, 9:46*am, Cecil Moore wrote:
wrote:
I'd have to make another one to compare
tilting it vertical, vs horizontal.

Again, I'm not talking about any loop in air. I'm only
one example of a ferrite rod loop antenna as exists in
AM radios. Those rods are mounted horizontal within the
radio while the polarization of the transmitted signal
is vertical.

I realize that, but I guess you missed the point.
The point being, I'm not so sure it wouldn't be
responding to mostly vertical polarization no
matter how the antenna was oriented,
unless maybe it was flipped on it's side.
The rods are mounted horizontal, but are
receiving a vertical signal off the ends.
You seem to imply a difference in pattern
using a ferrite bar, vs not using one.
I'm not so sure I agree with that without
more checking.
But like I say, I'd have to rig up some test
dummies to refresh myself.
But.. as I remember from the past versions I
made, the ones I made with air cores seemed
to act exactly the same as the ones with a
ferrite bar as far as pattern. IE: both are
bi-directional off each end and both are
responding to a vertical signal.