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ferrite cores for suppression of interference



 
 
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  #1  
Old December 26th 13, 04:49 AM posted to uk.tech.digital-tv
Bill Wright[_2_]
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Posts: 9,381
Default ferrite cores for suppression of interference

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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  #2  
Old December 26th 13, 07:48 AM posted to uk.tech.digital-tv
alan
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Posts: 173
Default ferrite cores for suppression of interference

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


--
mailto:news{at}admac(dot}myzen{dot}co{dot}uk
  #3  
Old December 26th 13, 07:55 AM posted to uk.tech.digital-tv
Bill Wright[_2_]
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Posts: 9,381
Default ferrite cores for suppression of interference

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
  #4  
Old December 26th 13, 08:34 AM posted to uk.tech.digital-tv
David Woolley[_2_]
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Posts: 550
Default ferrite cores for suppression of interference

On 26/12/13 08:55, Bill Wright wrote:

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.


Have you tried http://audiosystemsgroup.com/RFI-Ham.pdf?

Lots of graphs and written by a professional audio engineer for more
technically oriented amateurs.

The main difficulty, for its primary audience, is that getting small
quantities of the best ferrites for HF use is rather difficult in the
UK. That might be less of an issue in the case in question, depending
on whether the radio is LF or VHF.
  #5  
Old December 26th 13, 09:22 AM posted to uk.tech.digital-tv
Peter Crosland
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Posts: 524
Default ferrite cores for suppression of interference

On 26/12/2013 09:34, David Woolley wrote:
On 26/12/13 08:55, Bill Wright wrote:

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.


Have you tried http://audiosystemsgroup.com/RFI-Ham.pdf?

Lots of graphs and written by a professional audio engineer for more
technically oriented amateurs.

The main difficulty, for its primary audience, is that getting small
quantities of the best ferrites for HF use is rather difficult in the
UK. That might be less of an issue in the case in question, depending
on whether the radio is LF or VHF.


Thanks for that David. I don't need it now but a fantastic reference for
the future.

--
Peter Crosland
  #6  
Old December 26th 13, 09:31 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:


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 so have tended to use
the clip-on common mode blocks of ferrite. Or some of the RF filters which
have a small one of these surrounded by a delta of caps. All from CPC.

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.


Can be difficult as it depends on the ferrite, frequency, etc.

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


Nor I. However one of the difficulties is that this is an area where a
'filter' has to deal in poorly defined 'source' and 'load' impedances and
behaviour. So even given lots of formulas and a fancy computer you may find
that trial and error is faster and more reliable in the end. At least the
designs which have delta shunts either side help avoid that.

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
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #7  
Old December 26th 13, 09:22 PM posted to uk.tech.digital-tv
Bill Wright[_2_]
external usenet poster
 
Posts: 9,381
Default ferrite cores for suppression of interference

David Woolley wrote:

Have you tried http://audiosystemsgroup.com/RFI-Ham.pdf?


That seems at a glance to be excellent. I shall lock myself in the
lavatory for a hour or two when the six little terrors are here
tomorrow, and have a good read. Cheers.

Bill
  #8  
Old December 26th 13, 09:28 PM posted to uk.tech.digital-tv
Bill Wright[_2_]
external usenet poster
 
Posts: 9,381
Default ferrite cores for suppression of interference

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
  #9  
Old December 27th 13, 01:35 AM posted to uk.tech.digital-tv
Peter Crosland
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Posts: 524
Default ferrite cores for suppression of interference

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.


--
Peter Crosland
  #10  
Old December 27th 13, 04:12 AM posted to uk.tech.digital-tv
Bill Wright[_2_]
external usenet poster
 
Posts: 9,381
Default ferrite cores for suppression of interference

Peter Crosland wrote:

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.


Yes, of course. But it's always nice to know as much as it's possible to
know. I'd really prefer to have some measure of the effects of the ferrites.

Bill
 




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