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.

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 Jun 10, 5:00*pm, "D. Peter Maus" wrote:
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 for this Peter. I always thought that concept as an RF
resonator was suspect! :-D

On 6/11/10 10:10 , bpnjensen wrote:
On Jun 10, 5:00 pm, "D. Peter wrote:
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 for this Peter. I always thought that concept as an RF
resonator was suspect! :-D


It's not a bad thought. There are a number of antennae that are
made with a helical coil around a form. RF System's MTA is made this
way.

But we're talking many more turns, around a broader form, and a
tighter gathering of turns along the length to be practical as an
antenna.

On Jun 11, 8:32*am, "D. Peter Maus" wrote:
On 6/11/10 10:10 , bpnjensen wrote:





On Jun 10, 5:00 pm, "D. Peter *wrote:
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 for this Peter. *I always thought that concept as an RF
resonator was suspect! :-D

* *It's not a bad thought. There are a number of antennae that are
made with a helical coil around a form. RF System's MTA is made this
way.

* *But we're talking many more turns, around a broader form, and a
tighter gathering of turns along the length to be practical as an
antenna.- Hide quoted text -

- Show quoted text -

Indeed, something where the coil would become an actual inductor and
serve to provide additional electrical length where physical length is
restricted. Along with HF broadband antennas, mobile CB and ham
loaded antennas are typical examples of what you are talking about, I
assume - can't see much reason for this with an FM antenna, the lambda
being so short.

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

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.

On Thursday, June 10, 2010 at 2:55:22 PM UTC-5, 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

The helical spiral on modern antennas serves nothing more than to break up vortices created as air passes around the antenna. Also know as vortex induced vibration. Keeps the antenna from whipping. If you notice in the winter time when your car antenna gets ice on it, it starts to whip more violently. You see the same things on larger cylindrical structures and poles like smoke stacks and wind turbine towers.