Fixed Loop On-a-Roof - Great for Monitoring that Hard-to-Get AM/MW Radio Station
 

Telamon wrote:

In article .com,
"N9NEO" wrote:

Does higher bands mean like 160m is higher than 75m or 3.885MHz is
higher than 1.945MHz?

Would your Idea be practical Telamon considering the reverse voltage
capacitance of a varactor is limited to a small swing in PF? Maybe
lots of diodes in parallel?

Ack Ack, 12:59, back to work.

Well a couple of things come into play.

Local noise goes up, along with atmospheric, and loops tend to have
greater local noise rejection over a voltage type. This is especially
true for a shielded loop. There is no loop advantage in atmospheric
noise save for lightening storm noise so it might make a better summer
antenna.

The lower in frequency you go the signals tend to be directionally phase
stable and so with a loop receive pattern you can null signals.

The higher in frequency you go the less advantage there is in a loop
over a dipole but it will work just fine.

I think paralleling diodes to get more capacitance than what one diode
can provide will work. Can't think of a reason why it would not work.



Thats just what I was wondering. Thanks Telamon!

- Matt

Fixed Loop On-a-Roof - Great for Monitoring that Hard-to-Get AM/MW Radio Station
 

Telamon - Thank You !
and now I know one more fact - iane ~ RHF
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Fixed Loop On-a-Roof - Great for Monitoring that Hard-to-Get AM/MW Radio Station
 

Telamon wrote:

In article .com,
"N9NEO" wrote:

Does higher bands mean like 160m is higher than 75m or 3.885MHz is
higher than 1.945MHz?

Would your Idea be practical Telamon considering the reverse voltage
capacitance of a varactor is limited to a small swing in PF? Maybe
lots of diodes in parallel?

Ack Ack, 12:59, back to work.

Well a couple of things come into play.

Local noise goes up, along with atmospheric, and loops tend to have
greater local noise rejection over a voltage type. This is especially
true for a shielded loop. There is no loop advantage in atmospheric
noise save for lightening storm noise so it might make a better summer
antenna.

The lower in frequency you go the signals tend to be directionally phase
stable and so with a loop receive pattern you can null signals.

The higher in frequency you go the less advantage there is in a loop
over a dipole but it will work just fine.

I think paralleling diodes to get more capacitance than what one diode
can provide will work. Can't think of a reason why it would not work.



There are available diodes that can provide swings of more than 300 pF.

What is important, if you want tuning range, is the ratio of maximum
capacitance to minimum capacitance. Paralleling many identical diodes will
not change the ratio. Selecting the appropriate diode is better.

Fixed Loop On-a-Roof - Great for Monitoring that Hard-to-Get AM/MW Radio Station
 

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?

Fixed Loop On-a-Roof - Great for Monitoring that Hard-to-Get AM/MW Radio Station
 

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

Fixed Loop On-a-Roof - Great for Monitoring that Hard-to-Get AM/MW Radio Station
 

In article , craigm
wrote:

Telamon wrote:

In article .com,
"N9NEO" wrote:

Does higher bands mean like 160m is higher than 75m or 3.885MHz
is higher than 1.945MHz?

Would your Idea be practical Telamon considering the reverse
voltage capacitance of a varactor is limited to a small swing in
PF? Maybe lots of diodes in parallel?

Ack Ack, 12:59, back to work.

Well a couple of things come into play.

Local noise goes up, along with atmospheric, and loops tend to have
greater local noise rejection over a voltage type. This is
especially true for a shielded loop. There is no loop advantage in
atmospheric noise save for lightening storm noise so it might make
a better summer antenna.

The lower in frequency you go the signals tend to be directionally
phase stable and so with a loop receive pattern you can null
signals.

The higher in frequency you go the less advantage there is in a
loop over a dipole but it will work just fine.

I think paralleling diodes to get more capacitance than what one
diode can provide will work. Can't think of a reason why it would
not work.



There are available diodes that can provide swings of more than 300
pF.

What is important, if you want tuning range, is the ratio of maximum
capacitance to minimum capacitance. Paralleling many identical diodes
will not change the ratio. Selecting the appropriate diode is better.

The capacitance range may not be as great with the ganged diodes
depending on the diode specifications but it certainly is easier to use
one diode that has the need range.

One diode is 40 to 400 pF or four in parallel of 10 to 100 pF each
should work out to the same range. I just made up the numbers as an
example. In reality you could be correct because diodes in my example
may not exist. We were speaking in generality and not specifically.

--
Telamon
Ventura, California