In article sBEDc.1168$Rr2.4@lakeread03,
" Uncle Peter" wrote:

"CW" no adddress@spam free.com wrote in message
...
Yes, that is an advantage. Everytime someone asks a question about
a receive only antenna on this newsgroup, there are always many
responses saying to just put up a piece of wire and run it strait
to your radio. That will work, assuming that you live out in the
middle of nowhere, have no neighbors and have no electrical
appliances. For the rest of us, noise is a consideration and more
thought needs to be put into an antenna system.

How does the antenna differentiate between "noise" and a valid
signal?

Antennas are not intelligent agents able to differentiate between noise
and a broadcast signal. If the noise signal is generated a long
distance from the antenna it will be received right along with
broadcast signals. The only advantage some antennas would have here is
its reception pattern where the antenna could be orientated to be
relatively insensitive in the direction of the noise signal. This
generally is not helpful for short wave signals though because they are
generally too spread out directionally instead of looking like a point
source to take advantage of antenna nulls. Another problem for most
people is the fact that they cannot get the antenna up high enough for
it to exhibit its directional characteristics to a great degree.

A local noise is another matter greatly affecting many peoples
reception of short wave signals since many electronic devices around
the home and neighbor¹s homes generate noise. Here the type of antenna,
how it is connected to the receiver, and where it is located on the
user¹s property makes a huge difference on what may be heard.

Fundamentally, you want the entire antenna system to reject common mode
noise since to a local antenna this is the mode in which, the local
noise will couple to the antenna. You will want to use an antenna that
is balanced (Hertzian) instead of unbalanced (Marconi). You might also
want to consider using an antenna type that responds more to the
magnetic field component of the radio wave instead of the electric.
These two suggestions encompass the fact that most of the local noise
energy reaching and coupling to the antenna is a common mode electric
field and since the far field broadcast signals you want to receive is
composed of both electric and magnetic the later will be enhanced at
the expense of the former.

The connection from radio to antenna is best shielded so you would use
coax. You could use a balance line but they are harder to acquire, use,
and still will not work as well as coax shielding against local noise.

The antenna would be located as far from the majority of local noise
sources as possible on the property. Distance reduces the coupling to
local noise sources.

--
Telamon
Ventura, California

"Telamon" wrote in message
...
In article sBEDc.1168$Rr2.4@lakeread03,
" Uncle Peter" wrote:

How does the antenna differentiate between "noise" and a valid
signal?



SNIP


Fundamentally, you want the entire antenna system to reject common mode
noise since to a local antenna this is the mode in which, the local
noise will couple to the antenna. You will want to use an antenna that
is balanced (Hertzian) instead of unbalanced (Marconi). You might also
want to consider using an antenna type that responds more to the
magnetic field component of the radio wave instead of the electric.
These two suggestions encompass the fact that most of the local noise
energy reaching and coupling to the antenna is a common mode electric
field and since the far field broadcast signals you want to receive is
composed of both electric and magnetic the later will be enhanced at
the expense of the former.

The connection from radio to antenna is best shielded so you would use
coax. You could use a balance line but they are harder to acquire, use,
and still will not work as well as coax shielding against local noise.

The antenna would be located as far from the majority of local noise
sources as possible on the property. Distance reduces the coupling to
local noise sources.

--
Telamon
Ventura, California

You'd also have to decouple the coax shield from the antenna to
prevent signals or noise from carried on the outside of the shield
common-mode fashion from being coupled back into your
remotely located antenna.

Pete

"Telamon" wrote in message
...
In article sBEDc.1168$Rr2.4@lakeread03,
" Uncle Peter" wrote:

How does the antenna differentiate between "noise" and a valid
signal?



SNIP


Fundamentally, you want the entire antenna system to reject common mode
noise since to a local antenna this is the mode in which, the local
noise will couple to the antenna. You will want to use an antenna that
is balanced (Hertzian) instead of unbalanced (Marconi). You might also
want to consider using an antenna type that responds more to the
magnetic field component of the radio wave instead of the electric.
These two suggestions encompass the fact that most of the local noise
energy reaching and coupling to the antenna is a common mode electric
field and since the far field broadcast signals you want to receive is
composed of both electric and magnetic the later will be enhanced at
the expense of the former.

The connection from radio to antenna is best shielded so you would use
coax. You could use a balance line but they are harder to acquire, use,
and still will not work as well as coax shielding against local noise.

The antenna would be located as far from the majority of local noise
sources as possible on the property. Distance reduces the coupling to
local noise sources.

--
Telamon
Ventura, California

You'd also have to decouple the coax shield from the antenna to
prevent signals or noise from carried on the outside of the shield
common-mode fashion from being coupled back into your
remotely located antenna.

Pete

Telamon wrote:

A local noise is another matter greatly affecting many peoples
reception of short wave signals since many electronic devices around
the home and neighbor¹s homes generate noise. Here the type of antenna,
how it is connected to the receiver, and where it is located on the
user¹s property makes a huge difference on what may be heard.

Fundamentally, you want the entire antenna system to reject common mode
noise since to a local antenna this is the mode in which, the local
noise will couple to the antenna.

Yes!

You will want to use an antenna that
is balanced (Hertzian) instead of unbalanced (Marconi).

With an unbalanced antenna you must take more care to keep common mode
out of the feed system. It is not terribly hard, however, to reduce
common mode coupling to negligible levels, even with an unbalanced
antenna (see
http://www.anarc.org/naswa/badx/ante...e_antenna.html). One
may want an unbalanced system for other reasons. A balanced dipole close
to the ground generally has a poor vertical radiation pattern, while an
inverted-L is much better.

You might also
want to consider using an antenna type that responds more to the
magnetic field component of the radio wave instead of the electric.
These two suggestions encompass the fact that most of the local noise
energy reaching and coupling to the antenna is a common mode electric
field and since the far field broadcast signals you want to receive is
composed of both electric and magnetic the later will be enhanced at
the expense of the former.

This claim is widely made in the hobbyist literature, but I've never
seen any measurements to back it up. I've tried to check it myself, and
found the opposite: close to modern sources of EMI, the field tends to
be predominantly magnetic. You have to be very close the source to see
any effect at all: beyond ~0.1 wavelength induction balances the field
pretty effectively.

The connection from radio to antenna is best shielded so you would use
coax. You could use a balance line but they are harder to acquire, use,
and still will not work as well as coax shielding against local noise.

The antenna would be located as far from the majority of local noise
sources as possible on the property. Distance reduces the coupling to
local noise sources.

Yes!

-jpd

Telamon wrote:

A local noise is another matter greatly affecting many peoples
reception of short wave signals since many electronic devices around
the home and neighbor¹s homes generate noise. Here the type of antenna,
how it is connected to the receiver, and where it is located on the
user¹s property makes a huge difference on what may be heard.

Fundamentally, you want the entire antenna system to reject common mode
noise since to a local antenna this is the mode in which, the local
noise will couple to the antenna.

Yes!

You will want to use an antenna that
is balanced (Hertzian) instead of unbalanced (Marconi).

With an unbalanced antenna you must take more care to keep common mode
out of the feed system. It is not terribly hard, however, to reduce
common mode coupling to negligible levels, even with an unbalanced
antenna (see
http://www.anarc.org/naswa/badx/ante...e_antenna.html). One
may want an unbalanced system for other reasons. A balanced dipole close
to the ground generally has a poor vertical radiation pattern, while an
inverted-L is much better.

You might also
want to consider using an antenna type that responds more to the
magnetic field component of the radio wave instead of the electric.
These two suggestions encompass the fact that most of the local noise
energy reaching and coupling to the antenna is a common mode electric
field and since the far field broadcast signals you want to receive is
composed of both electric and magnetic the later will be enhanced at
the expense of the former.

This claim is widely made in the hobbyist literature, but I've never
seen any measurements to back it up. I've tried to check it myself, and
found the opposite: close to modern sources of EMI, the field tends to
be predominantly magnetic. You have to be very close the source to see
any effect at all: beyond ~0.1 wavelength induction balances the field
pretty effectively.

The connection from radio to antenna is best shielded so you would use
coax. You could use a balance line but they are harder to acquire, use,
and still will not work as well as coax shielding against local noise.

The antenna would be located as far from the majority of local noise
sources as possible on the property. Distance reduces the coupling to
local noise sources.

Yes!

-jpd

They don't but if you go by the advice you generally get on the antenna
group, you run an unshielded lead in (part of the antenna) right into the
shack (big noise source). When I made my prior comments about the lack of
consideration given to receive antenna, I was referring to the antenna
group. I didn't realize that the message was cross posted. It just amazes me
that they will debate a transmitting antenna to minute detail but receiving
antennas deserve no consideration other than a random piece of wire thrown
into a tree. Despite their often one sidedness I have learned a great deal
from them and mean no disrespect.


" Uncle Peter" wrote in message
news:sBEDc.1168$Rr2.4@lakeread03...

How does the antenna differentiate between "noise" and a valid signal?

They don't but if you go by the advice you generally get on the antenna
group, you run an unshielded lead in (part of the antenna) right into the
shack (big noise source). When I made my prior comments about the lack of
consideration given to receive antenna, I was referring to the antenna
group. I didn't realize that the message was cross posted. It just amazes me
that they will debate a transmitting antenna to minute detail but receiving
antennas deserve no consideration other than a random piece of wire thrown
into a tree. Despite their often one sidedness I have learned a great deal
from them and mean no disrespect.


" Uncle Peter" wrote in message
news:sBEDc.1168$Rr2.4@lakeread03...

How does the antenna differentiate between "noise" and a valid signal?

" Uncle Peter" wrote in message
news:HVKDc.1192$Rr2.241@lakeread03...

"Telamon" wrote in message
...
In article sBEDc.1168$Rr2.4@lakeread03,
" Uncle Peter" wrote:

How does the antenna differentiate between "noise" and a valid
signal?



SNIP


Fundamentally, you want the entire antenna system to reject common mode
noise since to a local antenna this is the mode in which, the local
noise will couple to the antenna. You will want to use an antenna that
is balanced (Hertzian) instead of unbalanced (Marconi). You might also
want to consider using an antenna type that responds more to the
magnetic field component of the radio wave instead of the electric.
These two suggestions encompass the fact that most of the local noise
energy reaching and coupling to the antenna is a common mode electric
field and since the far field broadcast signals you want to receive is
composed of both electric and magnetic the later will be enhanced at
the expense of the former.

The connection from radio to antenna is best shielded so you would use
coax. You could use a balance line but they are harder to acquire, use,
and still will not work as well as coax shielding against local noise.

The antenna would be located as far from the majority of local noise
sources as possible on the property. Distance reduces the coupling to
local noise sources.

--
Telamon
Ventura, California

You'd also have to decouple the coax shield from the antenna to
prevent signals or noise from carried on the outside of the shield
common-mode fashion from being coupled back into your
remotely located antenna.

Pete

Quite true.

" Uncle Peter" wrote in message
news:HVKDc.1192$Rr2.241@lakeread03...

"Telamon" wrote in message
...
In article sBEDc.1168$Rr2.4@lakeread03,
" Uncle Peter" wrote:

How does the antenna differentiate between "noise" and a valid
signal?



SNIP


Fundamentally, you want the entire antenna system to reject common mode
noise since to a local antenna this is the mode in which, the local
noise will couple to the antenna. You will want to use an antenna that
is balanced (Hertzian) instead of unbalanced (Marconi). You might also
want to consider using an antenna type that responds more to the
magnetic field component of the radio wave instead of the electric.
These two suggestions encompass the fact that most of the local noise
energy reaching and coupling to the antenna is a common mode electric
field and since the far field broadcast signals you want to receive is
composed of both electric and magnetic the later will be enhanced at
the expense of the former.

The connection from radio to antenna is best shielded so you would use
coax. You could use a balance line but they are harder to acquire, use,
and still will not work as well as coax shielding against local noise.

The antenna would be located as far from the majority of local noise
sources as possible on the property. Distance reduces the coupling to
local noise sources.

--
Telamon
Ventura, California

You'd also have to decouple the coax shield from the antenna to
prevent signals or noise from carried on the outside of the shield
common-mode fashion from being coupled back into your
remotely located antenna.

Pete

Quite true.

On Sun, 27 Jun 2004 19:55:58 -0700, "CW" no adddress@spam free.com
wrote:

When I made my prior comments about the lack of
consideration given to receive antenna, I was referring to the antenna
group. I didn't realize that the message was cross posted. It just amazes me
that they will debate a transmitting antenna to minute detail but receiving
antennas deserve no consideration other than a random piece of wire thrown
into a tree.

Hi OM,

As generalizations go, this one falls short with them all.

We here at rec.radio.amateur.antenna often recite the credo that
"reciprocity rules." This means that all considerations given to a
transmitting antenna are equally applied to receiving antennas.

However, I am sure you are responding to the disparity in coverage
between receiving and transmitting antennas - and this is for good
reason. Reception and Transmission are NOT reciprocal operations. A
receiver has far more latitude to accomplish its goal than does a
transmitter. Unless you have an abysmal receiver poorly connected to
an inadequate whip, the stock receiver with a simple length of wire is
often very close to doing a good job. If the receiver suffers from
any of a multitude of issues, there is generally a solution that
answers the problem specifically. About the only thing you can do for
the transmitter is to turn up the power, or lower the transmission
loss. It stands to reason that our focus is on optimizing the loss
side of the balance ledger.

Returning to the credo of "reciprocity rules," any gain to the
advantage of a transmitter is enjoyed by the receiver and the SWLer
stands the same advantage. But if that advantage is measured at 3dB,
this has the significance of 50W in 100W compared to the SWL S-Meter
change from S5 to S6 (BFD). Even though it is the same 3dB, there is
the illusion of perspective (my 50W compared to your 5µV). If the SW
station is buried in S9 noise, then this is not an antenna problem
(unless you can null the noise out through careful lobe positioning).
Filtering and/or DSP stand to answer the problem, but these are
obviously not remedies to transmission issues.

There is another thread discussing the goal of constructing a small
loop for 80M reception (and how well 5 turns might achieve some
benefit). The same issues of loss prevail for the comparison of
Radiation Resistance to Ohmic Resistance for a 1 Meter loop. The loop
Rr is in the thousandths of an Ohm and about on par for a small wire's
Ohmic loss. There's that 3dB again and what concerns the transmission
efficiency is far easier to tolerate with the receiver and its surplus
of gain. If the SWLer pays attention to this issue as it concerns the
transmission problems, then that SWLer stands to gain in the
efficiency returned. However, this is not to suggest that there is an
actual need to obtain this efficiency; but if the SWLer mismanages the
construction, the topic is discussed to the necessary depth to correct
it.

A simple basis of comparison will illustrate. Many SW radios have a
ferrite stick antenna that will work with at least some stations (VOA,
WWV, BBC and a host of others). Try transmitting through that same
ferrite stick and it will be like trying to shout through a straw.
Our only alternative is to add an amp, but the big KW is only going to
render smoke.

73's
Richard Clark, KB7QHC