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Use of type 31 ferrite as coax common mode choke



 
 
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  #11  
Old April 21st 08, 09:42 PM posted to rec.radio.amateur.antenna
J. Mc Laughlin
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Posts: 172
Default Use of type 31 ferrite as coax common mode choke

Dear Bruce: As a follow-up: No type 31 at Palomar. 73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"Bruce W. Ellis" wrote in message
...

On Mon, 21 Apr 2008 10:21:36 -0400, "J. Mc Laughlin"
wrote:

SNIP

P.S. I will also appreciate ideas about places to purchase ferrite in
addition to Mouser.


also check:
www.palomar-engineers.com

Bruce W0BF



  #12  
Old April 21st 08, 11:30 PM posted to rec.radio.amateur.antenna
Jim Lux
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Posts: 801
Default Use of type 31 ferrite as coax common mode choke

J. Mc Laughlin wrote:
Dear Jim:

Now I begin to see light. While type 31 must be at least three years old,
the world has not yet caught up to its existence.


the *amateur* world hasn't caught up.. I haven't looked, but I'd venture
that the ARRL handbook still doesn't mention it (if only because it
would be a expensive and herculean task to revise the entire handbook
every year). And, folks writing in QST tend not to be in the business,
so they're using what they learned in the handbook.

For instance, the RFI/EMC page on the arrl web site says:
"Original text reprinted from February and March 1992 QST "Lab Notes"
columns Copyright 1992 by the American Radio Relay League, Inc. All
rights reserved."

"Or, you can make a common-mode choke by wrapping 10 to 20 turns of the
antenna feed line or CATV cable through a ferrite toroid. Follow the
same procedure with the ac line. Use #75 (also known as "J"), #73 or #77
material if the interference is mainly from signals below 10 MHz. Use
#43 ferrite material for the higher bands or low VHF."

"To make a ferrite common-mode choke, wrap 5-10 turns of a conductor
onto an FT-240-43 ferrite core. (The "240" indicates that the outer
diameter of the core is 2.4"; the "43" designates the material. Other
materials may be useful, but 43 is a good all-around material.)"





(to be fair, they do link to K9YC's writeup)
  #13  
Old April 22nd 08, 03:59 AM posted to rec.radio.amateur.antenna
J. Mc Laughlin
external usenet poster
 
Posts: 172
Default Use of type 31 ferrite as coax common mode choke

Dear Jim: Thank you.

I had read an early version of K9YC's work. It was informative to read the
latest version. He does a good job.

It appears that my question may have had a positive effect and
radio-amateurs will consider type 31 for HF.

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"Jim Lux" wrote in message
...
J. Mc Laughlin wrote:
Dear Jim:

Now I begin to see light. While type 31 must be at least three years
old, the world has not yet caught up to its existence.


the *amateur* world hasn't caught up.. I haven't looked, but I'd venture
that the ARRL handbook still doesn't mention it (if only because it would
be a expensive and herculean task to revise the entire handbook every
year). And, folks writing in QST tend not to be in the business, so
they're using what they learned in the handbook.

For instance, the RFI/EMC page on the arrl web site says:
"Original text reprinted from February and March 1992 QST "Lab Notes"
columns Copyright 1992 by the American Radio Relay League, Inc. All
rights reserved."

"Or, you can make a common-mode choke by wrapping 10 to 20 turns of the
antenna feed line or CATV cable through a ferrite toroid. Follow the same
procedure with the ac line. Use #75 (also known as "J"), #73 or #77
material if the interference is mainly from signals below 10 MHz. Use #43
ferrite material for the higher bands or low VHF."

"To make a ferrite common-mode choke, wrap 5-10 turns of a conductor onto
an FT-240-43 ferrite core. (The "240" indicates that the outer diameter of
the core is 2.4"; the "43" designates the material. Other materials may be
useful, but 43 is a good all-around material.)"





(to be fair, they do link to K9YC's writeup)



  #14  
Old April 22nd 08, 05:16 AM posted to rec.radio.amateur.antenna
Roy Lewallen
external usenet poster
 
Posts: 1,374
Default Use of type 31 ferrite as coax common mode choke

J. Mc Laughlin wrote:
I looked through saved messages and the only reference to type 31 ferrite
(Fair-Rite) was in March of 2005. That reference had to do with ignition
wires.

Recommendations for HF choking ferrites have centered on the 70 series with
type 43 being favorably recommended for the upper portion of HF and VHF.
However, Fair-Rite seems to be recommending type 31 for HF. See Figure 26
in:
http://www.fair-rite.com/newfair/pdf/CUP%20Paper.pdf

Am I missing something? It seems to me that for the purpose of choking
common mode current (on the outside of the outer conductor of coax) from 3
to 25 MHz one should prefer the use of type 31. This is a receiving
application with a long run of coax.

73, Mac N8TT

P.S. I will also appreciate ideas about places to purchase ferrite in
addition to Mouser.


A fairly brief look at the graphs (Figs. 6 - 8) shows that type 31 has
roughly the same or a little higher total complex permeability than 73
over most of the lower HF range and same or higher than 43 on up to 100
MHz. So it should be a good ferrite to use for very wide band
applications. However, Table 1 shows that it's available in large parts
only. Type 43 is very widely available in a wide variety of sizes, so
you might have a lot more luck getting cores of the sizes you need in
type 43.

Roy Lewallen, W7EL
  #15  
Old April 22nd 08, 05:23 AM posted to rec.radio.amateur.antenna
Roy Lewallen
external usenet poster
 
Posts: 1,374
Default Use of type 31 ferrite as coax common mode choke

J. Mc Laughlin wrote:

P.S. I will also appreciate ideas about places to purchase ferrite in
addition to Mouser.


You might try Amidon (https://www.amidoncorp.com/) or the Wire Man
(http://thewireman.com/baluns.html#901). I don't think I've bought
anything from Amidon since Bill Amidon sold it, but see their brand on
small quantities of cores at the local electronics shop. Press Jones,
the Wire Man, is great to do business with.

Roy Lewallen, W7EL
  #16  
Old April 22nd 08, 08:01 AM posted to rec.radio.amateur.antenna
Ian White GM3SEK
external usenet poster
 
Posts: 233
Default Use of type 31 ferrite as coax common mode choke

Roy Lewallen wrote:

A fairly brief look at the graphs (Figs. 6 - 8) shows that type 31 has
roughly the same or a little higher total complex permeability than 73
over most of the lower HF range and same or higher than 43 on up to 100
MHz. So it should be a good ferrite to use for very wide band
applications. However, Table 1 shows that it's available in large parts
only. Type 43 is very widely available in a wide variety of sizes, so
you might have a lot more luck getting cores of the sizes you need in
type 43.

Roy Lewallen, W7EL



Amidon do stock some type 31 products, including FT-240-31 toroids and
the large beads for RG213, but they aren't listed on the website.

Part numbering is the same as normal, so simply substitute a "31" in the
part number you wish to order, and then call 1-800-898-1883.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
  #17  
Old April 22nd 08, 10:55 AM posted to rec.radio.amateur.antenna
Owen Duffy
external usenet poster
 
Posts: 1,169
Default Use of type 31 ferrite as coax common mode choke

"J. Mc Laughlin" wrote in
:

I looked through saved messages and the only reference to type 31
ferrite (Fair-Rite) was in March of 2005. That reference had to do
with ignition wires.


Mac,

Whilst playing around with models of a Guanella balun, I did compare #31
sleeves with Walt's design using #73 sleeves over the range 1 - 30MHz.

My model of Walt's balun is at http://www.vk1od.net/balun/W2DU/index.htm
.. I obtained different results to Walt's measurements, but I think that
is because Walt's measurements were affected by stray capacitance that
was worse than would apply to that type of balun in service.

I also modelled some Fair-rite 2631480002 sleeves and found a slightly
longer choke (12 cores at 25.4mm ea) was needed to achieve about the same
choking impedance up to about 12MHz, above which the #31 choke had higher
impedance than the #73 one.

Whilst I modelled these sleeves because they suited the application, I
have not seen anyone selling them in small quantities.

Owen

  #18  
Old April 22nd 08, 12:34 PM posted to rec.radio.amateur.antenna
Cecil Moore[_2_]
external usenet poster
 
Posts: 3,522
Default Use of type 31 ferrite as coax common mode choke

Owen Duffy wrote:
Whilst playing around with models of a Guanella balun, I did compare #31
sleeves with Walt's design using #73 sleeves over the range 1 - 30MHz.


Owen, have you done any experiments with 'K' material?
I have the Amidon AB240-250 Kit but haven't done
anything with it.
--
73, Cecil http://www.w5dxp.com
  #19  
Old April 22nd 08, 02:47 PM posted to rec.radio.amateur.antenna
JIMMIE
external usenet poster
 
Posts: 625
Default Use of type 31 ferrite as coax common mode choke

On Apr 21, 10:21*am, "J. Mc Laughlin" wrote:
I looked through saved messages and the only reference to type 31 ferrite
(Fair-Rite) was in March of 2005. *That reference had to do with ignition
wires.

Recommendations for HF choking ferrites have centered on the 70 series with
type 43 being favorably recommended for the upper portion of HF and VHF.
However, Fair-Rite seems to be recommending type 31 for HF. *See Figure 26
in:http://www.fair-rite.com/newfair/pdf/CUP%20Paper.pdf

Am I missing something? *It seems to me that for the purpose of choking
common mode current (on the outside of the outer conductor of coax) from 3
to 25 MHz one should prefer the use of type 31. *This is a receiving
application with a long run of coax.

73, * *Mac * N8TT

P.S. *I will also appreciate ideas about places to purchase ferrite in
addition to Mouser.

--
J. McLaughlin; *Michigan, USA
Home:


I think the type 31 is entended for use on things like power cords and
computer cables to prevent unwanted radiation/pickup of RF. Im not
sure how well it would meet your requirements but I suspect it may be
OK in a receive only situation. I have tried using some unknown types
of cores removed from various computer cables for a balun and the
vinyl tape holding them to the coax got very soft when they heated up.
Perhaps some experimentation using these cores is in order.

Jimmie
  #20  
Old April 22nd 08, 02:57 PM posted to rec.radio.amateur.antenna
JIMMIE
external usenet poster
 
Posts: 625
Default Use of type 31 ferrite as coax common mode choke

On Apr 22, 9:47*am, JIMMIE wrote:
On Apr 21, 10:21*am, "J. Mc Laughlin" wrote:





I looked through saved messages and the only reference to type 31 ferrite
(Fair-Rite) was in March of 2005. *That reference had to do with ignition
wires.


Recommendations for HF choking ferrites have centered on the 70 series with
type 43 being favorably recommended for the upper portion of HF and VHF.
However, Fair-Rite seems to be recommending type 31 for HF. *See Figure 26
in:http://www.fair-rite.com/newfair/pdf/CUP%20Paper.pdf


Am I missing something? *It seems to me that for the purpose of choking
common mode current (on the outside of the outer conductor of coax) from 3
to 25 MHz one should prefer the use of type 31. *This is a receiving
application with a long run of coax.


73, * *Mac * N8TT


P.S. *I will also appreciate ideas about places to purchase ferrite in
addition to Mouser.


--
J. McLaughlin; *Michigan, USA
Home:


I think the type 31 is entended for use on things like power cords and
computer cables to prevent unwanted radiation/pickup *of RF. Im not
sure how well it would meet your requirements but I suspect it may be
OK in a receive only situation. I have tried using some unknown types
of cores removed from various computer cables for a balun and the
vinyl tape holding them to the coax got very soft when they heated up.
Perhaps some experimentation using these cores is in order.

Jimmie- Hide quoted text -

- Show quoted text -


Apparently this testing has already been done.
Just google "type 31 ferrite" for results.

Jimmie
 




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