Radiomatt wrote:
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!

87.9 - 107.9

On 11/06/2010 7:43 PM, Radiomatt wrote:
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!

OK, then use the calculator on this website to readjust your figures if
you live or intend to live in those regions.

http://www.1728.com/freqwave.htm

88 - 108 is the most common. You will also note that my example of
100MHz is not exactly the centre of that spectrum but, for the purposes
of the exercise, close enough.

Krypsis

On 11/06/2010 11:49 PM, dave wrote:
Radiomatt wrote:
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!

87.9 - 107.9


What's a few KiloHertz between friends, eh?

Krypsis

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 Jun 11, 9:44*am, dave wrote:
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.

I know that.

OK, this deviates somewhat from the topic, but I've always wondered
about window antennas. My Mitsubishi Galant has an antenna embedded in
the rear window. It's not one of those dipoles that you used to (or
still?) see embedded in the front windshield of GM cars. Rather, it
has a peculiar folded design that's hard to describe. It works very
well. I get exceptional reception, especially on AM. In fact, one of
the reasons I chose the Galant is because it had the best AM reception
of all the cars I test drove. What's the theory on these window
antennas? Do they have a pre-amp ahead of the radio?

In message
,
Gregg writes
On Jun 11, 9:44*am, dave wrote:
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.

I know that.

I once made a helically compressed 80m halfwave dipole by winding each
leg of around 66' of PVC insulated wire on 33' of the type plastic line
used for rotary clothlines/airers (making sure, of course, that the
inner core was nylon, and not steel).

I marked the line every 6", and the wire every 1'. After a few false
starts, I soon got the knack of getting the spacing of the turns
correct. I suppose that diameter of the line was around 1/8", and I
needed to space the turns at around 3/8".

Obviously, I had dipole consisting of 132' of wire, but I have no idea
whether the turns were close enough to make a significant increase in
the inductance per unit length, thereby loading the antenna, and making
it electrically longer than a halfwave.

I only used the antenna once, at a scout 'Jamboree on the Air' event. I
put it up as an inverted V, with the centre at about 30', and the ends
at 20'. I used 300 ohm feeder. It was very sharply tuned (using a
balanced Z-match tuner). Daytime conditions on 80m were not very good,
but the antenna seemed particularly poor. I think I only managed a
couple of contacts, with only S5 reports where I would have expected
s9+.

40m was a bit better but, at the end of the day, just before we packed
up, things seemed distinctly lively on 20m. I got a 59 from 350 miles
away and, surprisingly, another from 40 miles (extremely short skip
conditions, it appeared, which may have explained the poor conditions on
80m).

I haven't bothered to try the antenna again. I have no idea if it was
working OK on 80m, and the poor performance was simply poor conditions.
I've still got it somewhere, so maybe one day, I'll get around to it.
--
Ian

DEFCON 88 wrote:
OK, this deviates somewhat from the topic, but I've always wondered
about window antennas. My Mitsubishi Galant has an antenna embedded in
the rear window. It's not one of those dipoles that you used to (or
still?) see embedded in the front windshield of GM cars. Rather, it
has a peculiar folded design that's hard to describe. It works very
well. I get exceptional reception, especially on AM. In fact, one of
the reasons I chose the Galant is because it had the best AM reception
of all the cars I test drove. What's the theory on these window
antennas? Do they have a pre-amp ahead of the radio?

Mine are crossed active loops at MF frequencies. Folded dipole at FM freqs.