In article EBJ5j.5593$gi7.4456@trnddc04,
"Dale Parfitt" wrote:

"Telamon" wrote in message
...
In article KCy5j.2781$md.534@trnddc06,
"Dale Parfitt" wrote:


Yes, for shortwave a 10-20 foot piece of wire can be used. You
do not need to spend a lot of money to get started. If noise is
an issue, google for 'shielded loop antenna'. You can also buy
more expensive antennas. Try,
http://www.universal-radio.com/catalog/sw_ant.html


Why would a shielded loop receive less noise than, say, a classic
wire turn loop?


Shielded loops are less sensitive to local inductive E fields.


I thought there was enough math/data out there that no one any longer
believed this.

From the W8JI page- http://www.w8ji.com/magnetic_receiving_loops.htm
"Folklore claims a small "shielded" loop antenna behaves like a
sieve, sorting "good magnetic signals" from "bad electrical noise".
Nothing is further from the truth! At relatively small distances a
small magnetic loop is more sensitive to electric fields than a small
electric field probe.


I would not be quoting some ham¹s web site as an authority on
electromagnetic theory or folklore.

There is a lot of bad information on the net. The areas of electronics
and electromagnetism are easy to misunderstand. Part of the problem is
that it is also easy to leave questions more open ended than intended
and so the answers tend to be ambiguous.

So now, I'll be more specific. Maybe it will help.

Small loops that have a shield that is split half way around are only
sensitive to magnetic fields. The split half way around ensures the E
field is canceled for far field and it works pretty well for near
inductive fields. I have used this type of probe along with small E
field probes in EMI and RFI work so I know they operate as they were
designed or I would not have been able to solve problems.

Another situation occurs when the shield is not split evenly around the
loop and grounded on one end. Here the outer shield picks up the E
field and the shielded wire picks up the M field and this configuration
will generate about two times the signal the center split shielded loop
will generate.

So it depends on a number of parameters not least of which is physical
size and electrical size for the application.

--
Telamon
Ventura, California

I would not be quoting some ham¹s web site as an authority on
electromagnetic theory or folklore.

You might want to Google Tom W8JI and find out who he is. To describe one of
the U.S.'s brighter engineers and designers as "some ham" is a real
disservice. The fact that he happens to have a ham license is purely a
coincidence. His explaination of how the shielded loop functions is embraced
by the IEEE group on Electromagnetics and Propagation, Roy Lewellen (writer
of EZNEC software) et al.
W4OP

In article ZRm6j.366$3s1.152@trnddc06,
"Dale Parfitt" wrote:


I would not be quoting some ham¹s web site as an authority on
electromagnetic theory or folklore.

You might want to Google Tom W8JI and find out who he is. To describe
one of the U.S.'s brighter engineers and designers as "some ham" is a
real disservice. The fact that he happens to have a ham license is
purely a coincidence. His explaination of how the shielded loop
functions is embraced by the IEEE group on Electromagnetics and
Propagation, Roy Lewellen (writer of EZNEC software) et al.

I don't care who Tom and Roy Lewellen are supposed to be. Credentials
don't impress me.

It's likely either they stated something incorrect or you misunderstood
them.

You asked a question and I answered it correctly. If you don't like the
answer go take it up with those two.

And by the way you will be glad to know I'm much more important than the
two of them together and yet I take the time to answer your questions.
I'm such a nice guy despite being the most important person you will
ever deal with.

Oh yeah, and your welcome Dale.

--
Telamon
Ventura, California

On Dec 7, 8:57 pm, "Dale Parfitt" wrote:


I would not be quoting some ham¹s web site as an authority on
electromagnetic theory or folklore.

You might want to Google Tom W8JI and find out who he is. To describe one of
the U.S.'s brighter engineers and designers as "some ham" is a real
disservice. The fact that he happens to have a ham license is purely a
coincidence. His explaination of how the shielded loop functions is embraced
by the IEEE group on Electromagnetics and Propagation, Roy Lewellen (writer
of EZNEC software) et al.
W4OP

W8JI's view, as I understand it, is that small shielded loops are no
less susceptible to local noise in virtue of their shielding, since
the shield, in his view, is part of the antenna. It's probably worth
pointing out that, even if this is true, it is still consistent with
the view that small loops pick up less noise than other types of
antennas in virtue of their directional characteristics. I guess W8JI
would then maintain that a shielded loop would be no less susceptible
to local noise than an unshielded loop, since in this case both
antennas enjoy the benefits of directionality; but he isn't commited
to denying that loops are quieter than, say whips when all things are
considered. Is this correct or am I missing something here?

W8JI's view, as I understand it, is that small shielded loops are no
less susceptible to local noise in virtue of their shielding, since
the shield, in his view, is part of the antenna. It's probably worth
pointing out that, even if this is true, it is still consistent with
the view that small loops pick up less noise than other types of
antennas in virtue of their directional characteristics. I guess W8JI
would then maintain that a shielded loop would be no less susceptible
to local noise than an unshielded loop, since in this case both
antennas enjoy the benefits of directionality; but he isn't commited
to denying that loops are quieter than, say whips when all things are
considered. Is this correct or am I missing something here?

Correct. Here it is from VE7SL perhaps more concisely:

Please note that a 'shielded loop' will not do anything to improve local
noise problems that any other type of loop (such as a multi-turn air core
loop) might do. Don't confuse the 'shielded' nomenclature with 'noise
shielding' as this is not the case. Like any other type of loop, it can be
used to null nearby noise sources or signals or turned to enhance desired
directions.
The shielded loop might more properly be called a 'two-turn' loop or a
'close coupled' loop as this more accurately describes it's behaviour. In
actual operation, it is the shield itself that is the active antenna
element. Signals picked up by the shield are coupled into the inner
conductor, which in turn are coupled back to the receiver via the preamp.
The loop is capable of good nulls on both groundwave and skywave signals.
The more 'balanced' the loop is (gap placed at exact center), the more
balanced the nulls will be.

In article CoC6j.3689$581.3625@trnddc04,
"Dale Parfitt" wrote:

W8JI's view, as I understand it, is that small shielded loops are no
less susceptible to local noise in virtue of their shielding, since
the shield, in his view, is part of the antenna. It's probably worth
pointing out that, even if this is true, it is still consistent with
the view that small loops pick up less noise than other types of
antennas in virtue of their directional characteristics. I guess W8JI
would then maintain that a shielded loop would be no less susceptible
to local noise than an unshielded loop, since in this case both
antennas enjoy the benefits of directionality; but he isn't commited
to denying that loops are quieter than, say whips when all things are
considered. Is this correct or am I missing something here?

Correct. Here it is from VE7SL perhaps more concisely:

Please note that a 'shielded loop' will not do anything to improve local
noise problems that any other type of loop (such as a multi-turn air core
loop) might do. Don't confuse the 'shielded' nomenclature with 'noise
shielding' as this is not the case. Like any other type of loop, it can be
used to null nearby noise sources or signals or turned to enhance desired
directions.
The shielded loop might more properly be called a 'two-turn' loop or a
'close coupled' loop as this more accurately describes it's behaviour. In
actual operation, it is the shield itself that is the active antenna
element. Signals picked up by the shield are coupled into the inner
conductor, which in turn are coupled back to the receiver via the preamp.
The loop is capable of good nulls on both groundwave and skywave signals.
The more 'balanced' the loop is (gap placed at exact center), the more
balanced the nulls will be.

This is wrong. I already explained why. Go back and read the part of my
post you cut out of the thread. You are being to general in the
description of shielded.

--
Telamon
Ventura, California

In article
,
Steve wrote:

On Dec 7, 8:57 pm, "Dale Parfitt" wrote:


I would not be quoting some ham¹s web site as an authority on
electromagnetic theory or folklore.

You might want to Google Tom W8JI and find out who he is. To describe one of
the U.S.'s brighter engineers and designers as "some ham" is a real
disservice. The fact that he happens to have a ham license is purely a
coincidence. His explaination of how the shielded loop functions is embraced
by the IEEE group on Electromagnetics and Propagation, Roy Lewellen (writer
of EZNEC software) et al.
W4OP

W8JI's view, as I understand it, is that small shielded loops are no
less susceptible to local noise in virtue of their shielding, since
the shield, in his view, is part of the antenna. It's probably worth
pointing out that, even if this is true, it is still consistent with
the view that small loops pick up less noise than other types of
antennas in virtue of their directional characteristics. I guess W8JI
would then maintain that a shielded loop would be no less susceptible
to local noise than an unshielded loop, since in this case both
antennas enjoy the benefits of directionality; but he isn't commited
to denying that loops are quieter than, say whips when all things are
considered. Is this correct or am I missing something here?


This is wrong. I already explained why. Go back and read the part of my
post Dale cut out of the thread.

--
Telamon
Ventura, California

This is wrong. I already explained why. Go back and read the part of my
post Dale cut out of the thread.

--
Telamon
Ventura, California

It was not my intent to cut censor your comments Telamon- I was attepmting
to clean up the thread and address Stece's question explicitely.
I respect your comments and we can agree to disagree as gentlemen.
73,
Dale