I might be able to assist you. I have a little experience with similar
problems in the San Diego Calif. desert. I dont know what your "standard
antenna" is. If your radio has no connections for attaching an external
antenna, there is little you can do to improve the AM reception.
If you want to get involved in amplified AM antennas, I might be of some
Thanks for the vote of confidence. But, I actually dont know how much
improvement the CCCrane add on antenna provides. That might be a 'fix' for
the Andrew V's poor reception. I understand their advertisement for their
$100.00 Twin ferrite antenna indicates that it will double the reception.
I would think doubling the output would be about 3 db. I didnt realize a 3
db gain antenna would be something that would be worth $100.00.
I'd like to hear from someone who has tried the CCCrane AM antenna.
The CC Crane is a ferrite antenna and RF amplifier. It requires a
9-volt battery and claims 32 dB of gain. The primary value of (low
noise) gain is to overcome noise and lack of gain in a mediocre
receiver -- so the worse the receiver the more it helps.
Being ferrite, it is probably an H-field antenna which would exhibit
some directionality. That's good: helps prefer a given signal over
external atmospheric and galactic noise.
Once an antenna captures enough signal + external noise to provide
signal significantly greater than the receiver's (or amplifier's)
internal noise, more antenna doesn't help until it is large enough to
have significant directional gain. At broadcast band, that's
hundreds of feet.
Making a low-noise broadcast band RF amp is simple, but probably more
than $100 worth of screwing around unless one enjoys building elex.
Sorry it took so long to get back ...I don't seem to have a lot of time to
read posts lately. What I'd like to do (if possible/practical) is set up
antenna(s) for am & fm to serve at least 2 recovers, both have external
antenna connections and have access to the same external wall on the house.
By standard antenna I mean the ones that came with the unit, also I'd like
to try the stringing wire method before I spend $$$ on some powered gadget.
What info do you need to better advise me?
Thanks ...and thanks to all that responded
All of my experience with commercial Amplified Antennas indicated that
they are usually not able to satisfactorily improve the system performance.
The concept of including an amplifier between the receiver and the antenna
is quite a good idea where transmission line loss is "unavoidable". There
is value in designing the receiver's input circuit so it can be adjusted to
accomodate whatever antenna impedance gets connected to it. But, that is
seldom done these days.
For your consideration - Since a car can get decent AM recption in your
neighborhood, there is adequet AM signal strength. I'd suggest that if you
have two antenna terminals in the back of a reasonably good household AM
receiver, you'll be able to construct a fairly simple antenna that works
well for all stations.
Can you locate the receiver close to where a long wire can be made
vertical and as long as practical? Then, can a wire be connected to a
ground (water pipe).
Dont be confused by thinking that the car antenna is just a short
telescoping element. The telescoping (short) mast is actually a probe that
couples to the car itself. The car is the antenna. The coax feed line in
the car is only a necesary component for minimizing induced noise. Dont
include any in the house radio antenna for AM.
For FM in remote locations, and in valleys, I have had some gtreat results
with simple home made Yagis. There are alot of web sites on Yagi antennas.
I am available for comments on any aspect of FM Yagi design. It seems so
easy to design and build FM Yagis, I'd encourage you to build a Yagi for
your FM needs. I would expect that you could design and build a Yagi that
performs better than the ones I've built. But, all those I've built have
have worked "good enough".
I dont know that viewing the telescoping element as the antenna and the
car body as the ground plane is wrong. But, at these wavelengths, it is
pretty difficult to identify what the antenna really is. Also, have you
noticed the car AM antennas that are imbeded in the windshield? Few cars
strive to keep the "aerials" vertical, but they all cars seem to work OK.
You can be pretty sure the AM signals are vertically polarized., so any
currents induced in a conductor will have resulted from their getting in the
way of a passing AM radio wave. Since there is more car than "car aerials"
it gets difficult to analyze just what is going on in a car radio antenna
for AM stations.
Jim, you are correct. The antenna is the vertical element and the
vehicle is the ground plane. That is why the coax is grounded at both
ends and one small open area causes noise. Some of the new antennas are
hidden in the glass with the defroster, or just in the glass around the
edge. Then there are diversity antennas that have 4 antennas embedded in
the bumper covers or other plastic trim. Those are connected to a box
that senses the different signal levels and uses the strongest. Anyone
who thinks otherwise doesn't know how a radio signal functions.
"jim rozen" <jim firstname.lastname@example.org> wrote in message
I'm surprized that you state that anyome who doesnt accept that the car is
a ground plane doesnt know how radio signals function.. I assume that you
agree that the impinging radio signal is vertically polarized. I asume you
also are considering cars that are only about 1 or 2 electrical degrees
high. Can a conductor that small (short) be considered a "Ground Plane"??
I didnt realize that cars had been equipped with an AM antenna systems
that select one or more of several probes in the trim and/or bumpers. That
seems to be unnecessary complexity, but it must provide some improvement.
Where can I find more information on the car that has the 4 embeded
The chassis of the vehicle is the ground plane of the antenna on every
vehicle I have ever seen. The vehicle height is not how the ground plane
is measured, it is measured by the amount of continuous connected
conductive surface area located around the antenna whip. That is also
why radio stations fade at different amounts based on which direction
the vehicle is headed. The different amount of ground plane relative to
the location of the whip on the vehicle changes the received signal
AM/FM broadcast signals are both vertically polarized. Have been for a
Lots of diversity equipped vehicles out there. Most of them are high end
luxury cars but there are a few pedestrian models as well. The town car
is one, Mercedes has a couple as well as BMW and Audi.
If you really want to see a strange antenna system take a look at the
ones used by XM and Sirius. Short vertical antenna to receive a circular
polarized signal that alters its angle of reflection as you move.
I used to think about antennas most of the working day. I still couldnt
refer to a car chassis as a "ground plane" for AM radio. It is just too
small. A car is in the vicinity of 1/100th of a wavelength. long, and half
that wide. That seems way too short to be worthy of being referred to as a
"ground plane", isnt it?.
There is alot of car information that has escaped my understanding. I
used to reserve the term "chassis" to describe the frame the cars body
bolted to. But, since that construction method isnt used much any more, I
guess you refer to the metal part of a car when you write "chassis".
You are apparently learning things I dont know about.
I thought we were considering AM radio for car antennas.
When did FM stations go to vertical polarization? I was thinking they
were circularly polarized.
On that "diversity equipped vehicle", do you suppose that diversity is
for satellite receiving antennas? I have problems with trying to imagine
how the radiation pattern at AM could be made directional, no matter where
it got "connected to" by the transmitter (or receiver). The car is just
too small in terms of wavelength to get directional.
You can feel free to use technical terms to tell me how the AM radio
signals are received by a car. There are alot of really well informed guys
on this news group. Even I thought I understood enough about car radio AM
antennas till you showed me that I dont to understand correctly.
Semantics! The vertical whip is an E-field probe, the body of the
car is a capacitive counterpoise for it to work against. An antenna
is a two-terminal network.
Steve, if the car body were a ground plane, then a radio connected
with its antenna terminal to the body and grounded to good earth
ground would receive no signal. What do you think would really
I was the one who first brought the term 'ground plane'
into the discussion. Of course a better term is counterpoise.
As you say, it's a two terminal antenna with the whip being
one terminal, and a steel plate of some indeterminate size,
more or less perpendicular to the whip, as the other terminal.
Counterpoise, reflector, etc. are better terms.
The impedance between the vehicle chasssis and the ground
is obviously pretty large.
please reply to:
I always figured that the polarization is pretty scrambled
by the time the car sees it. Other cars, phone and power wires
nearby, that sort of thing.
I remember making a 15 meter vertical antenna that was loaded
along its length and had a bunch of droopy ground radials. They
were supposed to be 1/4 L but they were shorter. The vertical
was helically wound on a stick with a short whip at the top.
That worked out pretty well.
I figure that the car radio manufacturers must load the input
circuit to get it near resonanace. There's no way that anything
car-sized is even going to come *close* to being a resonant
dipole at 1 mHz.
please reply to:
I'd bet that the guys who design AM antennas for cars dont think in terms
of making them resonant. They are just too small (short.). There is one
interesting design consideration that sometimes gets abused. It is the coax
lead that connects the "antenna' to the receiver. That feed line is seen by
the receiver as a capacitance that shunts the input terminals. And, since
the "antenna' looks like a highly capacitive load, the feed line capacitance
is shunting alot of signal from the receiver input. Some radio designers
used to provided a way to tune the combination of all the reactances for
each individual installations. I dont think thats done much any more.
I dont actually have any data on the polarization of AM (broadcast band)
radio waves. I do doubt that the horizontal component of any AM radio wave
can exist so close to the ground as where a car is.
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