I can speak from an experience I had.

I needed better reception on a car radio because I lived in a rural
area. This was years ago but might still apply

I installed a full height 1/4 wave cb whip antenna. I ran the same coax
that came with the original antenna. My radio had a tuning capacitor in
the back of it.

I peaked for maximum signal. Voila, it was much better.

If there is no tuning capacitor in the back of your radio, I suspect
this fix will not work at all.


wrote:
Hi all,

I've looked on the web, but with very little success. I have never
posted to this group before, so I apologize if my question is lame.

I listen to the Bay Area's KGO 810 MHz a lot. Their transmitter is
located in South San Fran Bay near the Dumbarton Bridge, and outpus 50
kW (that's what they say anyway). I am guessing, it's directed mostly
at the Pacific coast line. I often listen while driving east on I-80
to Truckee/Tahoe for skiing and camping. Usually the signal fades
substantially by the time I reach Sacramento - but it's still
tolerable listening (by ear, S/N of ~3). By the time I reach Auburn
it's essentially inaudible. Much better signal at night (~again, by
ear, S/N improves by ~2). At night, I can sort of pick up words in
truckee.

Question: can I *substantially* improve the S/N - say, factor of
2/5/10 by installing a better car antenna, so that, say, I could
listen in the Sierras day and night? I do not care if the antenna is
huge/geeky_looking, my car is being driven into the ground anyway. I
would be happy to make this a DIY project - to save on $ and learn
about radio. What kind of specs should I look for? I.e. I don't want
to go on the web and blindly buy an antenna advertised to "boost" your
AM radio reception - I would want some numbers.

I have limited knowledge in electronics, my background mostly is in
biophysics and biochemistry. So if you steer me into the right
direction I think I should be able figure it out.

On Jan 20, 8:30*pm, Dave wrote:
wrote:
On Jan 20, 11:29 am, JIMMIE wrote:

The current car I'm driving "Corolla" uses a small helically wound
antenna, which is at the rear of the roof. It's pretty short overall,
and I still have plenty of sensitivity.

Newer cars have active antennas.

I don't think mine is, but I'm not sure. It's basically the
same setup as any other antenna, just the whip is
shorter, and helically wound, I suppose for tuning purposes.
I guess it's about 15 or so inches long. I'd have to measure
it. Of course, it also functions for FM too.

"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

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