On Jun 10, 5:58*pm, bpnjensen wrote:
On Jun 10, 2:27*pm, Gregg wrote:





On Jun 10, 4:01*pm, bpnjensen wrote:

On Jun 10, 12:55*pm, Twitchell wrote:

I've seen some car radio whip antennas that look like they have a wire wrapped
around them. *The wraps are not close but lazily spiral down the length of the
antenna.

Does this help reception? *Is the coil attached somehow to the car or just the
antenna itself?

twitch

My antenna on my minivan is like that.

I think the supporting whip is fiberglas/or some insulating material,
and the wire is the actual electrical element; and in the interest of
saving length and providing strength, they wrap the wire around the
slightly shorter antenna pole. *The wire is then connected to the lead
of the antenna. *It works fine, about as good as a metal whip of
similar length. *Antennas for cars are pretty uncomplicated
critters... :-)

I can't believe I have never seen that before. Wouldn't there be a
chance for eventually the wire to work itself free, is it glued or
clipped to the whip?- Hide quoted text -

- Show quoted text -

Picture a thin pole (the whip) with a very gently coiled wrap of wire,
a turn every inch or so, from top to bottom. *Then, the entire thing
is covered with a wrap of something like shrink-wrap to hold it
altogether. *Unless the antenna is traumatized, the wire is pretty
much set for life.- Hide quoted text -

- Show quoted text -

Yeah OK, you didn't mention that is was encased, I thought it was
flowing freely in the wind, my post above mentioned what you just
said. ;-)

In article ,
Gregg says...

On Jun 10, 3:55=A0pm, Twitchell wrote:
I've seen some car radio whip antennas that look like they have a wire wr=
apped
around them. =A0The wraps are not close but lazily spiral down the length=
of the
antenna.

Does this help reception? =A0Is the coil attached somehow to the car or j=
ust the
antenna itself?

twitch

Hmm, I've never seen that. I have seen the radio whips that have wire
around them but they are then encased in plastic, like some CB
antennas are.

That's what I'm talking about...they're encased (sometimes) in plastic.

On 6/10/10 14:55 , Twitchell wrote:
I've seen some car radio whip antennas that look like they have a wire wrapped
around them. The wraps are not close but lazily spiral down the length of the
antenna.

Does this help reception? Is the coil attached somehow to the car or just the
antenna itself?

twitch



Chrysler started doing this a number of years ago on their fixed
length car antennae. Ford and GM do it, now also.

It appears as though there's a wire, under the black polymer
coating, wound around the metal post end to end. If you look very
closely, however, you see that the 'wire' ends just before the small
ball at the top and just before the hex fitting at the bottom. It
appears to be nothing more than a superficial contrivance.

In fact, it's there to break up the airflow around the antenna at
speed. Fixed length antenna made of the usual single piece steel rod
tends, under some conditions at speed to vibrate wildly both
loosening in it's fitting, and making unnecessary noises in the cab.
They also have an unfortunate tendency to whistle.

Chrysler started with a simple sheath with different aerodynamic
properties, made of plastic, slipped over the rod to eliminate these
properties. They made quite an issue of them in TV and billboard ads
in the 90's.

Ford suppliers, on the other hand, made the rod with this same
spiral twist on it's stainless steel antennae. Expensive, but
retaining the brightwork appearance of their traditional fixed
length antennae. And if you can find one, you'll see that the spiral
is actually manufactured into the surface of the rod, with a sharp
cut on one side of the spiral and a gentle slope blending into the
rod on the other. But this was expensive, and Ford, too, have gone
with the black polymer coating with what appears to be a wire embedded.

Since these antennae are all provided by an handful of suppliers,
all the car manufacturers using and fender mounted fixed length
antenna have gone with the black polymer coated spring steel rod,
with what appears to be a wire embedded.

This is for aerodynamics. Not for any electrical property.

"bpnjensen" wrote in message
...
On Jun 10, 12:55 pm, Twitchell wrote:
I've seen some car radio whip antennas that look like they have a wire
wrapped
around them. The wraps are not close but lazily spiral down the length of
the
antenna.

Does this help reception? Is the coil attached somehow to the car or just
the
antenna itself?

twitch

My antenna on my minivan is like that.

I think the supporting whip is fiberglas/or some insulating material,
and the wire is the actual electrical element; and in the interest of
saving length and providing strength, they wrap the wire around the
slightly shorter antenna pole. The wire is then connected to the lead
of the antenna. It works fine, about as good as a metal whip of
similar length. Antennas for cars are pretty uncomplicated
critters... :-)

Car antennas my be simple critters, but the coax used is special.
Mike

In article , D. Peter Maus says...

On 6/10/10 14:55 , Twitchell wrote:
I've seen some car radio whip antennas that look like they have a wire wrapped
around them. The wraps are not close but lazily spiral down the length of the
antenna.

Does this help reception? Is the coil attached somehow to the car or just the
antenna itself?

twitch



Chrysler started doing this a number of years ago on their fixed
length car antennae. Ford and GM do it, now also.

It appears as though there's a wire, under the black polymer
coating, wound around the metal post end to end. If you look very
closely, however, you see that the 'wire' ends just before the small
ball at the top and just before the hex fitting at the bottom. It
appears to be nothing more than a superficial contrivance.

In fact, it's there to break up the airflow around the antenna at
speed. Fixed length antenna made of the usual single piece steel rod
tends, under some conditions at speed to vibrate wildly both
loosening in it's fitting, and making unnecessary noises in the cab.
They also have an unfortunate tendency to whistle.

Chrysler started with a simple sheath with different aerodynamic
properties, made of plastic, slipped over the rod to eliminate these
properties. They made quite an issue of them in TV and billboard ads
in the 90's.

Ford suppliers, on the other hand, made the rod with this same
spiral twist on it's stainless steel antennae. Expensive, but
retaining the brightwork appearance of their traditional fixed
length antennae. And if you can find one, you'll see that the spiral
is actually manufactured into the surface of the rod, with a sharp
cut on one side of the spiral and a gentle slope blending into the
rod on the other. But this was expensive, and Ford, too, have gone
with the black polymer coating with what appears to be a wire embedded.

Since these antennae are all provided by an handful of suppliers,
all the car manufacturers using and fender mounted fixed length
antenna have gone with the black polymer coated spring steel rod,
with what appears to be a wire embedded.

This is for aerodynamics. Not for any electrical property.



Thanks. Your explanation makes sense and I guess there's no reason to
incorporate this into the whip antenna for a portable radio.

thanks again

twitch

On 11/06/2010 5:55 AM, Twitchell wrote:
I've seen some car radio whip antennas that look like they have a wire wrapped
around them. The wraps are not close but lazily spiral down the length of the
antenna.

Does this help reception? Is the coil attached somehow to the car or just the
antenna itself?

twitch

Looks to me like what you're seeing is a helical whip. They were used
most often on 27 Mhz CB radios. They often had a base loading coil at
the lower end. This would look like a solid piece of cylindrical pipe at
the base of the antenna.
The spiral of wire is the "active" element of the antenna. The whip
itself is usually made of fibreglass much akin to that which a fishing
rod is made from and has a support function. The assembly allows a
degree of flexibility without damage to the whip, the coil of wire, or
the mounting point, a feature necessary in mobile applications.
By spiralling the active element, you simulate the desired length of the
active element. In the 11 meter CB band, a quarter wave is about 9 feet.
Therefore, a 9 foot quarter wave aerial would be resonant in the 11
meter band thus having the best transmission and reception ability. A 9
foot aerial isn't practical in most automotive applications as they are
easily damaged or may damage other objects. The compromise then is to
helical wind the element. In most 11 meter applications, the helical
winding isn't sufficient so some extra matching is required. On some
helical whips, this takes the form of the windings being wound more
finely near the tip of the aerial (top loading). In other applications,
the resonance is achieved by a "loading coil" attached to the base of
the whip (bottom loading). It is said that top loading provides the best
results but I always preferred base loading coils for my applications.
I came across the last relic of my CB era the other day when I was
cleaning out my garage. It is an old magnetic base whip. It wasn't one
of the helical wound whips. Instead, it had a base loading coil and the
whip itself was about 5 feet of spring steel. It proved very useful in
the 70s when I was involved in desert rallying. Just attach it to any
vehicle, no drilling or mounting brackets required, and it used the
entire vehicle roof area as a "ground plane". Being magnetic, it was
somewhat less useful on some of the early Toyota Landcruisers with the
fibreglass rooves.

So, in summary, yes, it really does help reception as it provides a
better impedance match between vehicle and radio.

Krypsis

On 11/06/2010 7:06 AM, Twitchell wrote:
In ,
bpnjensen says...

On Jun 10, 12:55=A0pm, wrote:
I've seen some car radio whip antennas that look like they have a wire wr=
apped
around them. =A0The wraps are not close but lazily spiral down the length=
of the
antenna.

Does this help reception? =A0Is the coil attached somehow to the car or j=
ust the
antenna itself?

twitch

My antenna on my minivan is like that.

I think the supporting whip is fiberglas/or some insulating material,
and the wire is the actual electrical element; and in the interest of
saving length and providing strength, they wrap the wire around the
slightly shorter antenna pole. The wire is then connected to the lead
of the antenna. It works fine, about as good as a metal whip of
similar length. Antennas for cars are pretty uncomplicated
critters... :-)

I was wondering if I could improve my portable radio FM reception by wrapping it
like the car antenna by just wrapping it with a wire.

The FM band is 88 - 108 MHz. The wavelength for the centre of that band
(100MHz)is 9.8357 feet. A quarter of that is 2.458925 feet. Therefore,
a quarter wave whip needs to only be about 30 inches long to be resonant
in the FM band, a not unreasonable length for portable applications. I
seem to recall that most aerials on portable radios are approximately
that length when extended. You would only gain then if you desired to
have a shorter aerial than 30 inches yet still retain optimum reception
ability. I might add that, short of a lot of trial and error, you would
need to delve into aerial theory in order to even retain the reception
performance you currently experience.

Krypsis

Krypsis wrote:

The FM band is 88 - 108 MHz.

Hold on, young fella. That depends where in the world you are. Japan
uses 76–90 MHz, and the OIRT band in Eastern Europe is 65.8–74 MHz. It's
only the rest of the world that uses 88-108 MHz!

Twitchell wrote:
I've seen some car radio whip antennas that look like they have a wire wrapped
around them. The wraps are not close but lazily spiral down the length of the
antenna.

Does this help reception? Is the coil attached somehow to the car or just the
antenna itself?

twitch


No electrical purpose whatsoever. It keeps the whip from whistling in
the wind.

Gregg wrote:


Hmm, I've never seen that. I have seen the radio whips that have wire
around them but they are then encased in plastic, like some CB
antennas are.

On a Firestick, the wire is real.