In article , Mark Keith wrote:

Alfred E. Newman wrote:

John Doty's noise reducing antenna ideas from his 1993 posting are virtually
identical to noise reducimg antenna ideas found in articles by Denzil
Wraight and me which were published in DX News in 1991.

Decoupling a feedline is decoupling a feedline....

Denzil's article
was titled "Interference Reducing Antennas For The BCB," and mine was
"Inverted L Noise Reducing MF/VLF Antenna."

Is that an oximoron? Seriously...Using an omnidirectional antenna to
reduce *noise* on those bands is kinda counterproductive seems to me...

Denzil and I used twinlead
rather than coax. However, Mark Connelly published descriptions of similar
noise reducinmg antennas using coax in DX News later in 1991. These
articles are available from The National Radio Club http://www.nrcdxas.org/
as reprint A69. Contrary to what John claims, these kinds of noise reducing
antennas are not very effective against noise at SW frequencies much above 6
MHz.

Uhh...Decoupling a feedline is decoupling a feedline. No matter what
frequency...
You can do it at 440 mhz just fine... All my antennas are well
decoupled, and that includes from MW to 440 mhz.


These types of noise reducing antennas were invented by F. R. W.
Strafford in or about 1936, and he discusses these and other types of noise
reducing antennas for short waves in "Screened Aerials," Wireless World,
November 25, 1937, pages 516 - 518.

Decoupling the feedline has been around for quite a while...
I guess I have one issue though, and yes, I am anal retentive...I object
to *any* antenna being called a "low noise" antenna. Why? Cuz they don't
exist. These is no such thing. They should describe all of these types
of decoupled antenna schemes as "examples of better decoupled antenna
*systems*. The lower noise has nothing to do with the antenna itself.
Only the decoupling of the line, coax or ladder line. And to top this
off, if you are in a quiet area with no noise to pickup, using the
decoupling schemes will not do *anything* at all to reduce noise. The
performance will be exactly the same. IE: out in the woods, running
battery power, etc...A *true* noise reducing *antenna* would work
anywhere, but again, as far as I'm concerned, they don't exist. The on;y
way to really reduce noise using the antenna itself, would be to change
polarity. That would reduce an opposite polarized signal about 20 db or
so...
As far as the decoupling losing effectiveness over a certain freq, thats
a design issue with the decoupling scheme being used. Balun, chokes,
etc...BTW...I include the so called "shielded loops" with the "misnamed"
antenna group. In all tests I've ever run, I've never seen any
indication a shielded loop is any *quieter* to noise pickup than a
regular open loop. But the reason there is not due to decoupling of the
feedline per say, although a lack of decoupling can effect the overall
balance. It's due to the shielded loop providing inherent good balance
due to it's design. But if you have an open loop just as well balanced,
it will null noise sources just as well as a shielded loop. A shielded
loop is not any quieter to far field noise, than any other loop if you
are not using it to null the noise source. It *could* do a better job of
nulling that source, *if* the balance on the open loop was poorer, but
again, this is a design issue..You can design the open loop to be just
as balanced. MK

"...I object to *any* antenna being called a "low noise" antenna. Why?
Cuz they don't exist. These is no such thing."

Low noise antennas exist and one type is a shielded loop. The noise
improvement is from local noise sources not distant radiating far fields.

Inefficiently radiating local noise sources tend to spread out the
electric field where the magnetic field stays closer to the source.
These are induction fields not radiating fields. It is well known that
local noise source problems are due to common mode inductive electric
field pickup.

Mono-poles (Marconi 1/4 wave) and dipoles are examples of voltage
sensitive antennas. Loop or folded dipoles are examples of antennas
more sensitive to magnetic fields than electric.

A Mono-pole is great at picking up common mode electric fields and is
the worst type in noisy areas. It is very insensitive to local magnetic
fields.

Small unshielded loops are good at picking up local magnetic fields and
poor at picking up local electric fields. Shielding the loop makes it
even less sensitive to local electric fields.

Decoupling the unbalanced transmission line allow a balanced antenna to
stay that way. The balanced antenna is less sensitive to local common
mode electric fields.

Decoupling the transmission line helps prevent noise picked up on it's
outer shield from coupling to the antenna or noise from the mains
supply, through the radio and coax from coupling to the antenna.

If you don't live in the woods and if you or your neighbors have
electrically noisy electronic devices that radiate poorly but still
generate spread out electric common mode fields then the worst type to
best type relative to another is:

1. 1/4 wave Marconi mono-pole electric field sensitive unbalanced.

2. 1/2 wave dipole electric field field sensitive balanced antenna.

3. 1 wavelength or larger loop antenna which is a mix of electric and
magnetic field sensitive antenna. This antenna is balanced.

4. 1/10 wave or less loop antenna which is balanced, mostly magnetic
sensitive and has very poor electric field pickup.

5. 1/10 wave or less shielded loop which is generally better balanced
than unshielded and the least sensitive to local noise electric fields.

RELATIVELY SPEAKING "5" is a "low noise" antenna compared to "1" as far
as locally generated noise is concerned.

--
Telamon
Ventura, California