Antenna Polarization Question
 

I read that an AM BCB radio station transmits through a vertical antenna. If
this is true why does the signal diminish when i turn the ferrite rod
antenna & radio receiver in a vertical position?

Antenna Polarization Question
 

"Spin" wrote in message
...
I read that an AM BCB radio station transmits through a vertical antenna.
If this is true why does the signal diminish when i turn the ferrite rod
antenna & radio receiver in a vertical position?

I think you are confusing the polarity of the ferrite rod with the polarity
of the E field of the ferrite rod antenna- they are not the same.

Antenna Polarization Question
 

In message , Dale Parfitt
writes

"Spin" wrote in message
...
I read that an AM BCB radio station transmits through a vertical antenna.
If this is true why does the signal diminish when i turn the ferrite rod
antenna & radio receiver in a vertical position?

I think you are confusing the polarity of the ferrite rod with the polarity
of the E field of the ferrite rod antenna- they are not the same.


A classic non-answer, I think!

If someone asks question like this, I reckon that they probably know
nothing about E and H fields, and I would attempt to give a simple (but
essentially factual) answer using layman's terms.

So, Dale Parfitt, maybe you would like to have another try?
--
Ian

Antenna Polarization Question
 

Spin wrote:
I read that an AM BCB radio station transmits through a vertical antenna. If
this is true why does the signal diminish when i turn the ferrite rod
antenna & radio receiver in a vertical position?


Magnetic wave?

Antenna Polarization Question
 

"Spin" wrote in message
...
I read that an AM BCB radio station transmits through a vertical antenna.
If this is true why does the signal diminish when i turn the ferrite rod
antenna & radio receiver in a vertical position?


A ferrite rod antenna responds to the magnetic-field component of the radio
wave radiated by the transmitting station.

All significant AM medium-wave and long-wave stations use one or more
vertical conductors as their transmitting antenna and the current passing
through this conductor generates a magnetic field. The current path is
vertical so the resulting lines of magnetic force are loops surrounding this
vertical path - that is, loops in planes parallel to the surface of the
earth. Some distance away from the transmitting antenna, the outgoing radio
wave can be described by a magnetic field component aligned the same as
these loops, that is horizontal lines at any point of inspection, or by an
electric field component aligned perpendicularly, that is vertical. By
convention, the 'polarisation' of a single radio wave is the direction of
its electric field component and vertical polarisation is used for MW/LW
because it yields much better range for the same power than horizontal
polarisation (which would try to develop an electric field on the surface of
the conducting earth).

To couple power out from this radio wave requires a coil or loop to draw
current from the magnetic field or a dipole to derive voltage from the
electric field (from which to draw current). A coil couples to a magnetic
field when the lines of magnetic force pass through it ... so your ferrite
rod antenna works best when it is aligned with its axis horizontal.

Chris

.... let the flames begin!

Antenna Polarization Question
 

So in receiving the AM BCB frequencies in the united states, a vertical
antenna is 'generally' preferable over a horizontal antenna? The above is
based on having a receiver without any internal antenna.
"christofire" wrote in message
...

"Spin" wrote in message
...
I read that an AM BCB radio station transmits through a vertical antenna.
If this is true why does the signal diminish when i turn the ferrite rod
antenna & radio receiver in a vertical position?


A ferrite rod antenna responds to the magnetic-field component of the
radio wave radiated by the transmitting station.

All significant AM medium-wave and long-wave stations use one or more
vertical conductors as their transmitting antenna and the current passing
through this conductor generates a magnetic field. The current path is
vertical so the resulting lines of magnetic force are loops surrounding
this vertical path - that is, loops in planes parallel to the surface of
the earth. Some distance away from the transmitting antenna, the outgoing
radio wave can be described by a magnetic field component aligned the same
as these loops, that is horizontal lines at any point of inspection, or by
an electric field component aligned perpendicularly, that is vertical. By
convention, the 'polarisation' of a single radio wave is the direction of
its electric field component and vertical polarisation is used for MW/LW
because it yields much better range for the same power than horizontal
polarisation (which would try to develop an electric field on the surface
of the conducting earth).

To couple power out from this radio wave requires a coil or loop to draw
current from the magnetic field or a dipole to derive voltage from the
electric field (from which to draw current). A coil couples to a magnetic
field when the lines of magnetic force pass through it ... so your ferrite
rod antenna works best when it is aligned with its axis horizontal.

Chris

... let the flames begin!

Antenna Polarization Question
 

On Jan 20, 5:37*pm, "Spin" wrote:
So in receiving the AM BCB frequencies in *the united states, a vertical
antenna is 'generally' preferable over a horizontal antenna? The above is
based on having a receiver without any internal antenna.

If an AM BCB receiver has NO internal antenna, then almost ANY
external antenna will improve its AM BCB performance.

The greatest improvement in that performance will be achieved when the
intrinsic E or H gain of the receiving antenna matches that of the
radiated EM wave (in the US, or elsewhere).

RF

Antenna Polarization Question
 

Spin wrote:
So in receiving the AM BCB frequencies in the united states, a vertical
antenna is 'generally' preferable over a horizontal antenna? The above is
based on having a receiver without any internal antenna.

Not only the USA but world wide -- the laws of physics are the same
everywhere. During the day, propagation at BCB frequencies is by surface
wave. Only vertically polarized waves propagate this way, so all AM
broadcast stations use vertical antennas to produce vertically polarized
waves. These are best received with a vertically polarized antenna.

At night, AM broadcast signals can be propagated relatively long
distances by being reflected or refracted by the ionosphere. When that
happens, the polarization is rotated in a seemingly random fashion, so
horizontally polarized receiving antennas aren't at such a disadvantage.

Roy Lewallen, W7EL

Antenna Polarization Question
 

Richard Fry wrote:
. . .
The greatest improvement in that performance will be achieved when the
intrinsic E or H gain of the receiving antenna matches that of the
radiated EM wave (in the US, or elsewhere).

What's "intrinsic E or H gain"? In what way does it differ from gain
calculated relative to an isotropic source? How does one calculate the
gain of an EM wave?

Roy Lewallen, W7EL