folded dipoles
 

Do folded dipoles have better noise rejection than single wire dipoles. I
was looking at a drawing one day and realized that they are a dc short. I
know loop antennas are very good about noise.

Loop antennas are difficult to install and a folded dipole would be a lot
easier.

folded dipoles
 

B29 wrote:
Do folded dipoles have better noise rejection than single wire dipoles. I
was looking at a drawing one day and realized that they are a dc short. I
know loop antennas are very good about noise.

Loop antennas are difficult to install and a folded dipole would be a lot
easier.



Try this search:

http://groups.google.com/groups?hl=e...-8&sa=N&tab=wg
folded dipole noise reduction dipole - Google Groups

Chuck

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folded dipoles
 

B29 wrote:
Do folded dipoles have better noise rejection than single wire dipoles?

There's some controversy about that but here's my
take. Folded dipoles receive *electromagnetic noise*
just as well (or just as bad) as ordinary dipoles.
However, IMO, there is one type of noise that is not
as bad on folded dipoles as open-ended dipoles and
that is precipitation static noise defined at:

http://www.atis.org/tg2k/_precipitation_static.html

If a charged particle dumps its charge on the floating
wire of an open-ended bare wire dipole, there is only
one discharge path to the other side of the dipole
or to ground and that is through the transceiver.

However, if a charged particle dumps its charge on
one half of a folded dipole, there are two discharge
paths to the other half of the dipole, one through
the transceiver and one through the antenna wire.
The antenna wire discharge path is usually a lower
impedance than the discharge path through the
transceiver and the entire folded dipole is usually
referenced to ground.

In addition, we know that insulated airplane antennas
are less susceptible to precipitation static than
uninsulated airplane antennas. Folded dipoles are
often made out of insulated transmission line.
--
73, Cecil http://www.w5dxp.com

folded dipoles
 

chuck wrote:
Try this search:
http://groups.google.com/groups?hl=e...-8&sa=N&tab=wg
folded dipole noise reduction dipole - Google Groups

This posting of yours is at the top of the list. :-)
--
73, Cecil http://www.w5dxp.com

folded dipoles
 

Cecil Moore wrote:
Folded dipoles receive *electromagnetic noise*
just as well (or just as bad) as ordinary dipoles.

Sorry, that should be *electromagnetic wave noise*.
--
73, Cecil http://www.w5dxp.com

folded dipoles
 

On Mon, 18 Dec 2006 15:14:06 GMT, Cecil Moore wrote:
B29 wrote:
Do folded dipoles have better noise rejection than single wire dipoles?

rain static discussion
However, if a charged particle dumps its charge on
one half of a folded dipole, there are two discharge
paths to the other half of the dipole, one through
the transceiver and one through the antenna wire.

Three discharge paths --- if the folded dipole is grounded to a boom or
mast at the center point of its 'unbroken' side. (As is common with a
number of VHF yagis that employ folded (tubing) dipoles as the driven
element.)

It's my unscientific, unmeasured observation that my 2M yagi with a
folded dipole is bothered less by rain/snow static than my 6M,
'traditional dipole' yagi.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http//jonz.net/ng.htm

folded dipoles
 

Cecil Moore wrote:
B29 wrote:
Do folded dipoles have better noise rejection than single wire dipoles?

There's some controversy about that but here's my
take. Folded dipoles receive *electromagnetic noise*
just as well (or just as bad) as ordinary dipoles.
However, IMO, there is one type of noise that is not
as bad on folded dipoles as open-ended dipoles and
that is precipitation static noise defined at:

http://www.atis.org/tg2k/_precipitation_static.html

If a charged particle dumps its charge on the floating
wire of an open-ended bare wire dipole, there is only
one discharge path to the other side of the dipole
or to ground and that is through the transceiver.

Hello Cecil,

It is not certain that there will be a "discharge" (i.e., a change from
a charged state to a neutral one) at all. One possibility is that
charges on the wire will simply redistribute themselves after the
addition of a new charge. It also depends, obviously, on whether the
charged particle is of the same polarity as the preponderance of charges
that may already be on the antenna. My pet hypothesis is that these
charge redistributions cause changing magnetic fields which appear as
noise impulses in the receiver.

Remember from electrostatics that a grounded conductor, such as a tower
or an antenna, may not be at ground potential due to induction caused by
a cloud of oppositely charged particles, alien space ships, or whatever
charge concentration is in the vicinity of the conductor. Even though
the conductor is grounded! Of course, when the influence departs, the
grounded conductor returns to is neutral status.

Make sense? ;-)

Chuck


However, if a charged particle dumps its charge on
one half of a folded dipole, there are two discharge
paths to the other half of the dipole, one through
the transceiver and one through the antenna wire.
The antenna wire discharge path is usually a lower
impedance than the discharge path through the
transceiver and the entire folded dipole is usually
referenced to ground.

In addition, we know that insulated airplane antennas
are less susceptible to precipitation static than
uninsulated airplane antennas. Folded dipoles are
often made out of insulated transmission line.

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folded dipoles
 

chuck wrote:
It is not certain that there will be a "discharge" (i.e., a change from
a charged state to a neutral one) at all. Make sense? ;-)

I may be using the wrong word. By "discharge", I
didn't mean to imply that it would go to a neutral
state, just that a concentrated charge deposited
at a point on a conductor will be redistributed
over the entire conductor.
--
73, Cecil http://www.w5dxp.com

folded dipoles
 

Cecil Moore wrote:
chuck wrote:
It is not certain that there will be a "discharge" (i.e., a change
from a charged state to a neutral one) at all. Make sense? ;-)

I may be using the wrong word. By "discharge", I
didn't mean to imply that it would go to a neutral
state, just that a concentrated charge deposited
at a point on a conductor will be redistributed
over the entire conductor.

I do wonder whether alternatively the noise is not arcing or coronal
discharges caused by the buildup of these high potentials on an antenna.
An insulated antenna would resist charging and if charged, would have
less opportunity to discharge by arcing. The arcing could actually occur
in the receiver.

I have noticed that the precipitation static I sometimes hear sounds
very much like sand/dirt particles striking a glass window in a blow.
Data consistent with either hypothesis, I guess.

Chuck

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folded dipoles
 

If you think a DC short will reduce noise, why not just put an RF choke
or moderate value resistor across the feedline conductors of a
conventional dipole?

Roy Lewallen, W7EL

B29 wrote:
Do folded dipoles have better noise rejection than single wire dipoles. I
was looking at a drawing one day and realized that they are a dc short. I
know loop antennas are very good about noise.

Loop antennas are difficult to install and a folded dipole would be a lot
easier.