"Michael" ha scritto nel messaggio
. ..
is no tuning capacitor in the back of your radio, I suspect this fix will
not work at all.

Nobody prevent you to add it externally, i think.

BTW... curious to know if any ferrite antenna or 2x ferrite antennas in a
sort of cross-coupled way mounted in a waterproof container perform better
than whips. I goggled, but can't find a gain table for ferrite antennas vs.
dipole, or a medium dBI gain (negative, i suppose) for ferrite antennas
mounted into the commons consumer radios.

Chris, -.-. --.-

"-.-. --.-" wrote in message
...

"Michael" ha scritto nel messaggio
. ..
is no tuning capacitor in the back of your radio, I suspect this fix will
not work at all.

Nobody prevent you to add it externally, i think.

BTW... curious to know if any ferrite antenna or 2x ferrite antennas in a
sort of cross-coupled way mounted in a waterproof container perform better
than whips. I goggled, but can't find a gain table for ferrite antennas
vs. dipole, or a medium dBI gain (negative, i suppose) for ferrite
antennas mounted into the commons consumer radios.

Chris, -.-. --.-


Amongst several other factors, it depends how you combine the signals from
two crossed ferrite rods/coils - simple in-phase addition of their signals
won't yield a radiation pattern that is omni-directional in the horizontal
plane.

Magnetic antennas are sometimes considered beneficial for mobile reception
of medium/lomg-wave signals because they can be made insensitive to electric
fields, and evidence can be found of greater fluctuation of the electric
field of the wanted signal vs. the magnetic component. Also, some forms of
interference are found to present stronger electric fields than magnetic
ones. However, obtaining the requisite omni pattern isn't trivial.

Chris

christofire wrote:
Magnetic antennas are sometimes considered beneficial for mobile reception
of medium/lomg-wave signals because they can be made insensitive to electric
fields, ...

A magnetic antenna was used in all of the California
75m mobile antenna shootouts that I attended. I was
told it was to keep the close-by human bodies from
having an effect on the strength of the received signals.

Which leads me to a question: Most of us OFs have
witnessed the effects of human bodies on analog VHF
TV signals being received using rabbit ears. If we
used "magnetic rabbit ears", would the problem go
away? Is it only the electric field that varies when
an EM signal passes through a non-magnetic medium
like a human body - or a tree?
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
...
christofire wrote:
Magnetic antennas are sometimes considered beneficial for mobile
reception of medium/lomg-wave signals because they can be made
insensitive to electric fields, ...

A magnetic antenna was used in all of the California
75m mobile antenna shootouts that I attended. I was
told it was to keep the close-by human bodies from
having an effect on the strength of the received signals.

Which leads me to a question: Most of us OFs have
witnessed the effects of human bodies on analog VHF
TV signals being received using rabbit ears. If we
used "magnetic rabbit ears", would the problem go
away? Is it only the electric field that varies when
an EM signal passes through a non-magnetic medium
like a human body - or a tree?
--
73, Cecil http://www.w5dxp.com


I understand it becomes increasingly difficult to create a purely-magnetic
antenna as the frequency rises, and ferrite with the required properties
becomes progressively more expensive! Some VHF pagers used ferrite rods,
and one or two-turn coils. Screened one-turn loops are used in the
short-wave bands, by some amateurs as well as by the military (e.g. British
Royal Navy).

Chris

On Jan 21, 12:12*pm, "christofire" wrote:


I understand it becomes increasingly difficult to create a purely-magnetic
antenna as the frequency rises, and ferrite with the required properties
becomes progressively more expensive! *Some VHF pagers used ferrite rods,
and one or two-turn coils. *Screened one-turn loops are used in the
short-wave bands, by some amateurs as well as by the military (e.g. British
Royal Navy).

Chris

The way I look at it, there is no such thing as a "magnetic" antenna.
As an example, some call shielded single turn loops "magnetic"
antennas. They claim special properties such as lower noise reception.
But this is not the case. They receive the same s/n ratio as any other
single turn loop.
The only advantage the shield provides is inherently good balance.
Good balance improves the depth of the nulls.
But you can construct plain wire single turn loops to have just as
good balance if you use good construction.
I've side by side compared the two, and came to the conclusion
most of the theories about shielded or so called magnetic loops
to basically be a myth.

wrote:
The way I look at it, there is no such thing as a "magnetic" antenna.

Given that a transmitting dipole and a receiving dipole
transfer maximum signal when oriented in the same plane,
how does one explain a ferrite loop antenna receiving
maximum signal in a plane orthogonal to the transmitting
dipole?
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
...
wrote:
The way I look at it, there is no such thing as a "magnetic" antenna.

Given that a transmitting dipole and a receiving dipole
transfer maximum signal when oriented in the same plane,
how does one explain a ferrite loop antenna receiving
maximum signal in a plane orthogonal to the transmitting
dipole?
--
73, Cecil http://www.w5dxp.com


Ampere's circuital law and the well-known 'right-hand rule'.

Chris

On Jan 21, 3:11*pm, Cecil Moore wrote:
wrote:
The way I look at it, there is no such thing as a "magnetic" antenna.

Given that a transmitting dipole and a receiving dipole
transfer maximum signal when oriented in the same plane,
how does one explain a ferrite loop antenna receiving
maximum signal in a plane orthogonal to the transmitting
dipole?
--
73, Cecil *http://www.w5dxp.com

I'm not sure without looking into it, but I notice this with
both shielded, and unshielded loops.
As an example, my 44 inch per side 5 turn diamond
loop prefers to be fed horizontally vs vertically
when receiving MW stations which use a vertical
transmit antenna.
IE: I feed it at the middle lowest corner.
If I feed it at a side corner, which would be vertically fed,
I seem to remember it not working near as well.
Do you consider an open small loop "unshielded" a
"magnetic" antenna? Some do, but I tend not to.
They act the same as the shielded loops that many
seem to call "magnetic" antennas.
The ability to respond to mostly the magnetic field
vs the electric field only pertains to the very near field
within about 1/10 wavelength.
Within 1 wavelength they often respond more to the
electrical wave. In the far field they should respond
to both fields the same as any other antenna.
Or this is my current understanding anyway.. :/
So using any type of "magnetic" antenna for the OP's
purpose would seem to be a waste of time unless
they are trying to reduce noise pickup that is within
1/10 of a wavelength away.
I know myself that these small loops are still quite
capable of picking up local noise, just like most
any other antenna. The only advantage are the sharp
nulls which you use to get rid of said noise.
If your mobile tests were within 1/10 of a wave,
maybe it makes more sense. But I'm not sure if
I can see any advantage to trying to receive a far
field signal vs any other antenna unless the nulls
are useful.

wrote in message
...
On Jan 21, 12:12 pm, "christofire" wrote:


I understand it becomes increasingly difficult to create a purely-magnetic
antenna as the frequency rises, and ferrite with the required properties
becomes progressively more expensive! Some VHF pagers used ferrite rods,
and one or two-turn coils. Screened one-turn loops are used in the
short-wave bands, by some amateurs as well as by the military (e.g.
British
Royal Navy).

Chris

The way I look at it, there is no such thing as a "magnetic" antenna.
As an example, some call shielded single turn loops "magnetic"
antennas. They claim special properties such as lower noise reception.
But this is not the case. They receive the same s/n ratio as any other
single turn loop.
The only advantage the shield provides is inherently good balance.
Good balance improves the depth of the nulls.
But you can construct plain wire single turn loops to have just as
good balance if you use good construction.
I've side by side compared the two, and came to the conclusion
most of the theories about shielded or so called magnetic loops
to basically be a myth.


I believe the issue is that if an open loop isn't perfectly balanced then it
will respond to an electric field, acting as a monopole. Then, when the
loop is oriented so the magnetic field of a signal should be in one of its
nulls, the cancellation may be incomplete because of sensivity to the
electric field component of that signal. Screening the loop overcomes this
effect so it could be claimed that screening improves the balance, although
this isn't what's really happening.

With a pair of screened loops and a whip it is possible to receive
separately the magnetic and electric fields associated with a radio signal
and to record their strengths at different locations. This can reveal
significant differences on account of building and electrical clutter, but
only if the loop is adequately screened. No myth!

Chris

On Thu, 22 Jan 2009 01:06:28 -0000, "christofire"
wrote:

With a pair of screened loops and a whip it is possible to receive
separately the magnetic and electric fields associated with a radio signal
and to record their strengths at different locations. This can reveal
significant differences on account of building and electrical clutter, but
only if the loop is adequately screened. No myth!

What you describe is a direction finding system with a general antenna
that can be switched in to sniff for a transmitter to take a bearing
on. A commonplace design for this application. The loops are no more
screened than any other, and careful observation of their construction
details would reveal the necessary break in the screen which serves
for balance only. Any claims to magnetic field separation are, as
Mark well put it, a myth.

The only way you could achieve this separation is by traveling at the
speed of light with your antenna in that magnetic field, at its 90
degree peak to the electric field null. This reduces the topic from
the status of myth to that of absurd.

73's
Richard Clark, KB7QHC