RHF wrote:


Usually getting the Element of the Loop Antenna at least
Three Feet above the Roof (Five Feet is better) will get
the Loop out of the Building's RFI / EMF Noise Envelop.


What technical foundation exists for this type of statement?

craigm

CraigM,

Why - Elevate the Antenna Element 3-5 Feet Above the Roof ?
http://groups.yahoo.com/group/Shortw...a/message/9443

Just basic practical experience on my part and
what I have read and been told over the years.

FWIW - Elevating the Antenna Element 3-5 Feet 'above' the
Roof may not always work in providing a Stronger Signal and
Less Noise in all situations - but often it does.

In general this statement applies to any Antenna Element
around a House or Building or their Roof Line and Attic.

Where 'possible' get the Antenna Element :
* Off-the-Surface
* Away-from-the-Surface
* Out-and-Up-in-the-Air
A few Feet of Space {Distance} Does Matter

The Why - It just may result from the simple fact that as
the Distance {Space} from a Source-of-Noise Increases
the Signal Level of the Noise Decreases.

So 'if' there is some Wiring or Equipment (Source-of-Noise)
in the Attic Area : The Surface of the Roof would be closer
and the Noise Stronger then if it were detected another 3-5
Feet away (Up Higher in the Air).

Note - This 'assumes' a non-metal Roof Surface that may act
as a Shield for any Noise emanating from the Attic of House.

It goes without saying that 'if' there is Electrical Equipment
on the Roof like Swamp-Coolers or Air-Conditioners then it
is always a good idea (were practical) to place the Antenna
Element away from such potential Sources-of-Noise.

In Conclusion - It remains my recommendation that "Elevating"
the Antenna Element 3-5 Feet 'above' the Surface of the Roof
is the better place for it to be for a Cleaner RF Signal and
Reduced Noise from the interior of the House.

as always - iane ~ RHF

In article , craigm
wrote:

RHF wrote:


Usually getting the Element of the Loop Antenna at least
Three Feet above the Roof (Five Feet is better) will get
the Loop out of the Building's RFI / EMF Noise Envelop.


What technical foundation exists for this type of statement?

Most any building materials have a dielectric constant higher than air
(1) and tend to bend the electric field lines around the house. The
field lines generated inside penetrating the outside tend to head toward
earth.

--
Telamon
Ventura, California

Telamon - Thank You !
and now I know one more fact - iane ~ RHF
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Telamon wrote:

In article , craigm
wrote:

RHF wrote:


Usually getting the Element of the Loop Antenna at least
Three Feet above the Roof (Five Feet is better) will get
the Loop out of the Building's RFI / EMF Noise Envelop.


What technical foundation exists for this type of statement?

Most any building materials have a dielectric constant higher than air
(1) and tend to bend the electric field lines around the house. The
field lines generated inside penetrating the outside tend to head toward
earth.


Are you saying the wood, fiberglass and shingles have enough effect to make
three or five foot separation sufficient to reduce the field from noise
generated inside a house?

Why then would anyone have trouble with noise radiated from their neighbor's
house?

In article , craigm
wrote:

Telamon wrote:

In article , craigm
wrote:

RHF wrote:


Usually getting the Element of the Loop Antenna at least Three
Feet above the Roof (Five Feet is better) will get the Loop out
of the Building's RFI / EMF Noise Envelop.


What technical foundation exists for this type of statement?

Most any building materials have a dielectric constant higher than
air (1) and tend to bend the electric field lines around the house.
The field lines generated inside penetrating the outside tend to
head toward earth.


Are you saying the wood, fiberglass and shingles have enough effect
to make three or five foot separation sufficient to reduce the field
from noise generated inside a house?

It is not a reduction as much as additional bending (refraction) of the
field lines to follow the contour of the house to earth so the field
strength falls off faster than it otherwise would without the
difference in dielectric constant between the building materials and
air.

There is always some dielectric heating loss to add to that but at 1 to
30 MHz it would be very small.

If noise from your neighbors house is bothering you there is a good
chance it is diminished when it rains if the noise is radiating
directly from the neighbors house because the building material
dielectric constant would be much higher than when it is dry.

Why then would anyone have trouble with noise radiated from their
neighbor's house?

Usually because the radiated noise induces currents in other nearby
conductors around like gutters, utility lines that then re-radiate the
noise.

Some of the noise is EMI through common AC mains connections.

Some of the noise generation is also RFI (far field) to begin with
instead of just near field energy.

--
Telamon
Ventura, California