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ferrite cores for suppression of interference



 
 
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  #11  
Old December 27th 13, 08:20 AM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 7,250
Default ferrite cores for suppression of interference

Well, I've not had huge success. For example a couple of turns in every lead
of my sub woofer got rid of Radio China International, but I still pick up
the mobile phone galloping ghost noises.
The closer to the actual source in a lead the better it works, IE, its
better on the offending bit than the bit it is offending in my experience.
Apart from that, I'm not convinced that its a cure, it adds inductance and
limits the frequency, but it certainly does not stop crap from crap devices
getting into all sorts of things.


There seems also to be an issue with the way many devices supply low
voltage dc along long cables from psus at the plug end which are switch
mode. I suspect the crap is radiated by the leead, but its strange that its
only when its plugged into theswitched off item.
I think interference is a very very black art to tackle in any way that
works all the time

Maybe I need to live in a faraday cage with my own generator.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Bill Wright" wrote in message
...
Anyone with any practical experience of this? I'm trying to put something
together that's based on real life experience.

Bill



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  #12  
Old December 27th 13, 08:27 AM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 7,250
Default ferrite cores for suppression of interference

The problem is that in most situations, there are a lot of variables to
consider, cables at different supply voltages and some ac and some dc and
the proximity of other cables the earthing or otherwise of interconnected
devices etc, and often the fix seems to just not follow sensible logic.
I have a shaver charger that no matter where in the house you plug it in, it
causes crap to be heard on sensitive inputs of things and all over the lf
bands. The weir part is that its no better where you locate it, This makes
me think its not transmitting stuff from its wire but directly through the
mains. . You cannot put a Ferrite on it as it plugs directly in.


Brian

--
From the Sofa of Brian Gaff Reply address is active
"Bill Wright" wrote in message
...
alan wrote:
On 26/12/2013 05:49, Bill Wright wrote:
Anyone with any practical experience of this? I'm trying to put
something together that's based on real life experience.

Bill


My fm car radio was picking up a lot of noise from anything plugged into
a 12V to 5V USB power supply.
http://tinyurl.com/nlhrt3s
I tried a few different designs/brands of USB adapters and it was the
same with any equipment plugged in (mobile phone, sat nav etc.).

I fitted 2 off split ring ferrite cores to the +ve and -ve supply behind
the 'cigarette lighter' socket, 2 off cores to the +ve and -ve supply to
the radio and 1 off over the thin aerial coax wire. The problem was
completely solved. I'm don't know which one had the most effect. As it
was a struggle to remove and replace the radio and fascia I just fitted
all 5 at the same time.

The ferrites open up so that they can be clipped around a wire without
having to disconnect or cut the wire. All were fitted as close as
possible to the radio and cigarette lighter socket.
Similar in appearance to
http://tinyurl.com/oqvg8nk
but the ones I used were 25 long and took a 4/5mm cable



Interesting. I'm wondering about the relative merits of the clip-on type
and the larger ring type where you wind the cable through the ring mebbe
six to ten times.

There has to be some sort of way of calculating or estimating the
resistance of different ferrites to the common mode RF at different
frequencies.

I'm struggling with this. There doesn't seem to be much info around,
except that I found some very highbrow stuff full of formulae that I
couldn't begin to understand.

I don't like the 'black art' approach.

Bill



  #13  
Old December 27th 13, 08:32 AM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 7,250
Default ferrite cores for suppression of interference

I also notice quite a few appliances already have these o n their cables
nowadays, TVs, phone chargers etc, but few, if any have anything on the
mains side which is often wher e the crap comes out from. Better design
needed?

Brian

--
From the Sofa of Brian Gaff Reply address is active
"Bill Wright" wrote in message
...
Jim Lesurf wrote:
In article , Bill Wright
wrote:

Interesting. I'm wondering about the relative merits of the clip-on type
and the larger ring type where you wind the cable through the ring
mebbe six to ten times.


In recent years I've not found any of the large rings


Both RS and CPC sell them. The RS list of them has a very peculiar pricing
structure. The CPC ones only go up to a bout 30mm OD. I sent off for a few
to experiment with. I have plenty of the clip on ones, and have used them
with some degree of success, but I'm curious about the larger ones.

Bill



  #14  
Old December 27th 13, 08:59 AM posted to uk.tech.digital-tv
David Woolley[_2_]
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Posts: 550
Default ferrite cores for suppression of interference

On 27/12/13 09:20, Brian Gaff wrote:

Apart from that, I'm not convinced that its a cure, it adds inductance and
limits the frequency, but it certainly does not stop crap from crap devices
getting into all sorts of things.


As stated in the reference I quoted, if correctly designed for the
problem frequency, ferrite chokes should appear resistive, not
inductive. They should be operated in a range where the ferrite is lossy.

  #15  
Old December 27th 13, 10:55 AM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
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Posts: 4,326
Default ferrite cores for suppression of interference

In article , Bill Wright
wrote:
Jim Lesurf wrote:
In article , Bill Wright
wrote:

Interesting. I'm wondering about the relative merits of the clip-on
type and the larger ring type where you wind the cable through the
ring mebbe six to ten times.


In recent years I've not found any of the large rings


Both RS and CPC sell them. The RS list of them has a very peculiar
pricing structure. The CPC ones only go up to a bout 30mm OD.


Thanks for pointing that out. I looked a couple of years ago and couldn't
find any. I plan to buy some stuff from CPC in the New Year so I'll add
this to my list.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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Audio Misc http://www.audiomisc.co.uk/index.html

  #16  
Old December 27th 13, 11:13 AM posted to uk.tech.digital-tv
Johny B Good[_2_]
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Posts: 853
Default ferrite cores for suppression of interference

On Fri, 27 Dec 2013 09:32:11 -0000, "Brian Gaff"
wrote:

I also notice quite a few appliances already have these o n their cables
nowadays, TVs, phone chargers etc, but few, if any have anything on the
mains side which is often wher e the crap comes out from. Better design
needed?


No. That's as good as it gets. Think about it. Placing the ferrite
loading on the output side not only blocks mains borne interference
but also PSU generated noise as well.
--
Regards, J B Good
  #17  
Old December 27th 13, 12:06 PM posted to uk.tech.digital-tv
tony sayer
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Posts: 5,001
Default ferrite cores for suppression of interference

In article , Peter
Crosland scribeth thus
On 26/12/2013 22:28, Bill Wright wrote:
Jim Lesurf wrote:
In article , Bill Wright
wrote:

Interesting. I'm wondering about the relative merits of the clip-on type
and the larger ring type where you wind the cable through the ring
mebbe six to ten times.

In recent years I've not found any of the large rings


Both RS and CPC sell them. The RS list of them has a very peculiar
pricing structure. The CPC ones only go up to a bout 30mm OD. I sent off
for a few to experiment with. I have plenty of the clip on ones, and
have used them with some degree of success, but I'm curious about the
larger ones.


Whilst I understand your concern in this case it really is a "suck it
and see approach" that is needed. There are just too many variables for
anything else to bring success.



Bill

What are you trying to suppress give us the requirements and we might be
able to help better..

--
Tony Sayer


  #18  
Old December 27th 13, 05:14 PM posted to uk.tech.digital-tv
tony sayer
external usenet poster
 
Posts: 5,001
Default ferrite cores for suppression of interference

In article , Brian Gaff
scribeth thus
Well, I've not had huge success. For example a couple of turns in every lead
of my sub woofer got rid of Radio China International, but I still pick up
the mobile phone galloping ghost noises.
The closer to the actual source in a lead the better it works, IE, its
better on the offending bit than the bit it is offending in my experience.
Apart from that, I'm not convinced that its a cure, it adds inductance and
limits the frequency, but it certainly does not stop crap from crap devices
getting into all sorts of things.


For RF pickup you really need to get at the first semiconductor device
and do a bit if RF bypassing, that will cure it..



--
Tony Sayer




  #19  
Old December 27th 13, 06:43 PM posted to uk.tech.digital-tv
Bill Wright[_2_]
external usenet poster
 
Posts: 9,381
Default ferrite cores for suppression of interference

Brian Gaff wrote:

Maybe I need to live in a faraday cage.


I for one will cheerfully come and push bananas through the bars for you.

Bill
  #20  
Old December 27th 13, 06:54 PM posted to uk.tech.digital-tv
Bill Wright[_2_]
external usenet poster
 
Posts: 9,381
Default ferrite cores for suppression of interference

Brian Gaff wrote:
The problem is that in most situations, there are a lot of variables to
consider, cables at different supply voltages and some ac and some dc and
the proximity of other cables the earthing or otherwise of interconnected
devices etc, and often the fix seems to just not follow sensible logic.
I have a shaver charger that no matter where in the house you plug it in, it
causes crap to be heard on sensitive inputs of things and all over the lf
bands. The weir part is that its no better where you locate it, This makes
me think its not transmitting stuff from its wire but directly through the
mains. . You cannot put a Ferrite on it as it plugs directly in.


I had almost total success in dealing with the noise radiated by the
reversing camera's LCD monitor in the motorhome. It was almost wiping
out FM. I pulled a tubular length of mesh over the whole aerial lead and
grounded it heavily at both ends. The fact that this worked showed that
the screening on the aerial's own lead was ineffective, I suppose.

Bill
 




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