When such a ferrite cylinder is slid over shielded cable of a laptop supply
cable, ie one conductor housed within a sheathing and the ferrite around the
outside of that

On Tue, 2 Mar 2010 08:40:39 -0000, "N_Cook" wrote:

When such a ferrite cylinder is slid over shielded cable of a laptop supply
cable, ie one conductor housed within a sheathing and the ferrite around the
outside of that

Of course they work. No sane manufactory would intentionally design
cables with giant blobs near the ends.

There are multiple flavors of material, composition, size, and shape.
The ferrite clamp on cylinder that I think you're referring to is
usually necesary to prevent the laptop and the switching power supply,
from radiating EMI and RFI. The FCC gets rather irate when that
happens. Everything will work without the ferrite cylinder, but will
not pass Part 15.

http://www.howstuffworks.com/question352.htm


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote in message
...
On Tue, 2 Mar 2010 08:40:39 -0000, "N_Cook" wrote:

When such a ferrite cylinder is slid over shielded cable of a laptop
supply
cable, ie one conductor housed within a sheathing and the ferrite around
the
outside of that

Of course they work. No sane manufactory would intentionally design
cables with giant blobs near the ends.

There are multiple flavors of material, composition, size, and shape.
The ferrite clamp on cylinder that I think you're referring to is
usually necesary to prevent the laptop and the switching power supply,
from radiating EMI and RFI. The FCC gets rather irate when that
happens. Everything will work without the ferrite cylinder, but will
not pass Part 15.

http://www.howstuffworks.com/question352.htm


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

I can see a simple insulated pair of cables fed through and looping around a
few times within a ferrite ring working, but does a cylinder over shielding
work. ?

"N_Cook" wrote in message
...
Jeff Liebermann wrote in message
...
On Tue, 2 Mar 2010 08:40:39 -0000, "N_Cook" wrote:

When such a ferrite cylinder is slid over shielded cable of a laptop
supply
cable, ie one conductor housed within a sheathing and the ferrite around
the
outside of that

Of course they work. No sane manufactory would intentionally design
cables with giant blobs near the ends.

There are multiple flavors of material, composition, size, and shape.
The ferrite clamp on cylinder that I think you're referring to is
usually necesary to prevent the laptop and the switching power supply,
from radiating EMI and RFI. The FCC gets rather irate when that
happens. Everything will work without the ferrite cylinder, but will
not pass Part 15.

http://www.howstuffworks.com/question352.htm


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

I can see a simple insulated pair of cables fed through and looping around
a
few times within a ferrite ring working, but does a cylinder over
shielding
work. ?



I guess it would be a bit dumb of the manufacturers to imagine that they do,
and then waste their money fitting them on the *offchance* that they do. I
imagine that the testing bodies would have rapidly told them if they didn't
accomplish what they were put there for ...

Arfa

Arfa Daily wrote in message
...

"N_Cook" wrote in message
...
Jeff Liebermann wrote in message
...
On Tue, 2 Mar 2010 08:40:39 -0000, "N_Cook" wrote:

When such a ferrite cylinder is slid over shielded cable of a laptop
supply
cable, ie one conductor housed within a sheathing and the ferrite
around
the
outside of that

Of course they work. No sane manufactory would intentionally design
cables with giant blobs near the ends.

There are multiple flavors of material, composition, size, and shape.
The ferrite clamp on cylinder that I think you're referring to is
usually necesary to prevent the laptop and the switching power supply,
from radiating EMI and RFI. The FCC gets rather irate when that
happens. Everything will work without the ferrite cylinder, but will
not pass Part 15.

http://www.howstuffworks.com/question352.htm


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

I can see a simple insulated pair of cables fed through and looping
around
a
few times within a ferrite ring working, but does a cylinder over
shielding
work. ?



I guess it would be a bit dumb of the manufacturers to imagine that they
do,
and then waste their money fitting them on the *offchance* that they do. I
imagine that the testing bodies would have rapidly told them if they
didn't
accomplish what they were put there for ...

Arfa



At one time I did a lot of materials testing to BS standards and over the
years we came across a few significant errors that got into the published
standards. I doubt things are much different in other sets of standards.
conjecture
Someone notes that these cylinders suppress harmonics of greater than 100
Mhz compared to nothing added on very lossy , little metal coverage, wire;
so stipulates they must be added to all such wires

On Mar 2, 5:14*am, "N_Cook" wrote:
Arfa Daily wrote in message

...







"N_Cook" wrote in message
...
Jeff Liebermann wrote in message
.. .
On Tue, 2 Mar 2010 08:40:39 -0000, "N_Cook" wrote:

When such a ferrite cylinder is slid over shielded cable of a laptop
supply
cable, ie one conductor housed within a sheathing and the ferrite
around
the
outside of that

Of course they work. *No sane manufactory would intentionally design
cables with giant blobs near the ends.

There are multiple flavors of material, composition, size, and shape..
The ferrite clamp on cylinder that I think you're referring to is
usually necesary to prevent the laptop and the switching power supply,
from radiating EMI and RFI. *The FCC gets rather irate when that
happens. *Everything will work without the ferrite cylinder, but will
not pass Part 15.

http://www.howstuffworks.com/question352.htm

--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558

I can see a simple insulated pair of cables fed through and looping
around
a
few times within a ferrite ring working, but does a cylinder over
shielding
work. ?

I guess it would be a bit dumb of the manufacturers to imagine that they
do,
and then waste their money fitting them on the *offchance* that they do.. I
imagine that the testing bodies would have rapidly told them if they
didn't
accomplish what they were put there for ...

Arfa

At one time I did a lot of materials testing to BS standards and over the
years we came across a few significant errors that got into the published
standards. I doubt things are much different in other sets of standards.
conjecture
Someone notes that these cylinders suppress harmonics of greater than 100
Mhz compared to nothing added on very lossy , little metal coverage, wire;
so stipulates they must be added to all such wires- Hide quoted text -

- Show quoted text -

The ferrite cylinders provide a high impedance for common-mode
emissions coming from the source onto the cable so that the cable does
not act as an antenna/wire. It should have no effect on signals
traveling on the cable that are "balanced". The cylinder is just an
elongated toroid, and the additional material raises the common-mode
impedance more at the lower frequencies. A series of smaller toroids
would have the same effect at lower frequencies, and would probably be
even more effective at higher frequencies. There are a LARGE number
of ferrite compositions, designed to have peak impedance at various
frequencies, and to have a "high Q" or a "low Q", depending on what
frequenciesa are needed to be suppressed. And as another poster said,
tha manufacturers would not go to the trouble and expense if they did
not have to. Back in the 1970's, when I first got into EMC, there
were complaints about interference to airplanes in the Baltimore
Washington area, and it was traced to computers. That led to the
first FCC rules on interference. Eventually we issued ANSI C63.4 in
conjunction/cooperation with the FCC, setting up rules on how to make
measurements to ensure standards were used to measure equipment to the
FCC emission limits.

I worked in this area for 40+ years before retiring from Bell Labs 10
years ago. I am still on ANSI C63 and various IEEE EMC Society
committees. In that 50-year time, emissions have increased from the 1
- 100 MHz area up to the 10 MHz - 10 GHz area. WIth the increase in
frequency, it has become harder to shield noise as the smallest
openings that were not a problem at 10 MHz become slot antennas at 10
GHz. Ferrites are now being incorporated into the connectors
themselves as putting them on to cables allows for noise to be
radiated from the short stretch of cable between the connector and the
point of application of the ferrite. Good design will help reduce the
problem, but there aren't enough well-trained EMC designers/engineers
out in the field. The IEEE EMC Society is constantly working to get
more engineers interested in the field. It is hard to get people
interested in something they cannot feel, see, hear, smell or touch.
But it's a fun way to be an engineer!

hr(bob) wrote in message
...
On Mar 2, 5:14 am, "N_Cook" wrote:
Arfa Daily wrote in message



The ferrite cylinders provide a high impedance for common-mode
emissions coming from the source onto the cable so that the cable does
not act as an antenna/wire. It should have no effect on signals
traveling on the cable that are "balanced". The cylinder is just an
elongated toroid, and the additional material raises the common-mode
impedance more at the lower frequencies. A series of smaller toroids
would have the same effect at lower frequencies, and would probably be
even more effective at higher frequencies. There are a LARGE number
of ferrite compositions, designed to have peak impedance at various
frequencies, and to have a "high Q" or a "low Q", depending on what
frequenciesa are needed to be suppressed. And as another poster said,
tha manufacturers would not go to the trouble and expense if they did
not have to. Back in the 1970's, when I first got into EMC, there
were complaints about interference to airplanes in the Baltimore
Washington area, and it was traced to computers. That led to the
first FCC rules on interference. Eventually we issued ANSI C63.4 in
conjunction/cooperation with the FCC, setting up rules on how to make
measurements to ensure standards were used to measure equipment to the
FCC emission limits.

I worked in this area for 40+ years before retiring from Bell Labs 10
years ago. I am still on ANSI C63 and various IEEE EMC Society
committees. In that 50-year time, emissions have increased from the 1
- 100 MHz area up to the 10 MHz - 10 GHz area. WIth the increase in
frequency, it has become harder to shield noise as the smallest
openings that were not a problem at 10 MHz become slot antennas at 10
GHz. Ferrites are now being incorporated into the connectors
themselves as putting them on to cables allows for noise to be
radiated from the short stretch of cable between the connector and the
point of application of the ferrite. Good design will help reduce the
problem, but there aren't enough well-trained EMC designers/engineers
out in the field. The IEEE EMC Society is constantly working to get
more engineers interested in the field. It is hard to get people
interested in something they cannot feel, see, hear, smell or touch.
But it's a fun way to be an engineer!

*****

But is that still the case where the wire is coaxial with a thick layer of
metal, shielding the core wire? This type is high current carrying coaxial
wire , not signal level co-axial cable which can have relatively open mesh
shielding.

In article ,
N_Cook wrote:

I can see a simple insulated pair of cables fed through and looping around a
few times within a ferrite ring working, but does a cylinder over shielding
work. ?

It's the equivalent of a one-turn winding on a ring. Yes, it will
work, at least to some extent The amount of inductive reactance and
series resistance it adds to common-mode current flow on the outside
of the cable will depend on the size, the ferrite mix, and the
frequency.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
N_Cook wrote:

But is that still the case where the wire is coaxial with a thick layer of
metal, shielding the core wire? This type is high current carrying coaxial
wire , not signal level co-axial cable which can have relatively open mesh
shielding.

Yes. You can (and do) get current flowing on the *outside* of the
shield - an unbalanced flow. Common-mode chokes such as these
ferrites are intended to block this type of current flow.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article , (Dave Platt) wrote:
In article ,
N_Cook wrote:

I can see a simple insulated pair of cables fed through and looping around a
few times within a ferrite ring working, but does a cylinder over shielding
work. ?

It's the equivalent of a one-turn winding on a ring. Yes, it will
work, at least to some extent The amount of inductive reactance and
series resistance it adds to common-mode current flow on the outside
of the cable will depend on the size, the ferrite mix, and the
frequency.


For the thing to works, a certain amount of current flow needs
to exist On a high Z line they do nothing. You need bypass caps for that,
or combinations of inductors and caps.

greg

On Mar 2, 11:03*am, "N_Cook" wrote:
hr(bob) wrote in message

...
On Mar 2, 5:14 am, "N_Cook" wrote:

Arfa Daily wrote in message

The ferrite cylinders provide a high impedance for common-mode
emissions coming from the source onto the cable so that the cable does
not act as an antenna/wire. *It should have no effect on signals
traveling on the cable that are "balanced". *The cylinder is just an
elongated toroid, and the additional material raises the common-mode
impedance more at the lower frequencies. *A series of smaller toroids
would have the same effect at lower frequencies, and would probably be
even more effective at higher frequencies. *There are a LARGE number
of ferrite compositions, designed to have peak impedance at various
frequencies, and to have a "high Q" or a "low Q", depending on what
frequenciesa are needed to be suppressed. *And as another poster said,
tha manufacturers would not go to the trouble and expense if they did
not have to. *Back in the 1970's, when I first got into EMC, there
were complaints about interference to airplanes in the Baltimore
Washington area, and it was traced to computers. *That led to the
first FCC rules on interference. *Eventually we issued ANSI C63.4 in
conjunction/cooperation with the FCC, setting up rules on how to make
measurements to ensure standards were used to measure equipment to the
FCC emission limits.

*I worked in this area for 40+ years before retiring from Bell Labs 10
years ago. I am still on ANSI C63 and various IEEE EMC Society
committees. In that 50-year time, emissions have increased from the 1
- 100 MHz area up to the 10 MHz - 10 GHz area. *WIth the increase in
frequency, it has become harder to shield noise as the smallest
openings that were not a problem at 10 MHz become slot antennas at 10
GHz. *Ferrites are now being incorporated into the connectors
themselves as putting them on to cables allows for noise to be
radiated from the short stretch of cable between the connector and the
point of application of the ferrite. *Good design will help reduce the
problem, but there aren't enough well-trained EMC designers/engineers
out in the field. *The IEEE EMC Society is constantly working to get
more engineers interested in the field. *It is hard to get people
interested in something they cannot feel, see, hear, smell or touch.
But it's a fun way to be an engineer!

*****

But is that still the case where the wire is coaxial with a thick layer of
metal, shielding the core wire? This type is high current carrying coaxial
wire , not signal level co-axial cable which can have relatively open mesh
shielding.

Yes, the ferrite is effective for any common mode signals that occur
when the outbound signal on the center conductor is not EXACTLY equal
to the return on the outer conductor/shield. Any net difference
between the two signal levels is common mode and that is what the
ferrite will reduce by increasing the common mode impedance.

On Mar 2, 12:40*am, "N_Cook" wrote:
When such a ferrite cylinder is slid over shielded cable ...

Mostly, these are inductors to suppress common-mode RF
currents, but they are also made lossy (like a resistor
coupled to a secondary winding), so they dampen
ringing.

Even if the cable is already shielded, the shield is
a potential antenna. Damping the antenna current is
sometimes necessary.

On Mar 2, 12:40*am, "N_Cook" wrote:
When such a ferrite cylinder is slid over shielded cable of a laptop supply
cable, ie one conductor housed within a sheathing and the ferrite around the
outside of that

I think they work great. I made a hat out of them, and almost all of
the voices have stopped.