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