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!

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 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 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