Use of type 31 ferrite as coax common mode choke
J. Mc Laughlin
(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: J...@power-net.net
Cecil Moore
> 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.
Did you find any information on their fancy
'K' material?
--
73, Cecil http://www.w5dxp.com
Richard Clark
<j...@power-net.net> wrote:
>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.
Hi Mac,
I can't say that I have any familiarity with type 31, but certainly
the rest and others. My reference is a 13 year old hard-copy that
does not have this material listed, so it is hard to make side-by-side
comparisons for like-sized beads. Looking at the other charts it
would seem that type 31 would have less "bulk" Z (it would take more
beads at any particular frequency to equal other formulations).
As for your application, and if it is a particularly long run along
ground, or underground, ground itself may provide sufficient snubbing
of Common Mode currents. Except, of course, 60Hz which could be
particularly vicious and I would recommend running a parallel bare
ground wire to the remote ground. In that regard, you may even need
tri-ax.
73's
Richard Clark, KB7QHC
Jim Lux
Fair-rite 31 mix is a new one specifically developed for RF choking
applications. As you mention, it has a huge range of frequencies for
which it's useful. The recommendations one sees in older literature for
73, 43, etc, were formulated back before the new mix was available. Of
course, once something is written, it gets copied over and over without
a lot of thought being put into whether the underlying assumptions are
still met: in this case, what mixes are available.
Page 888 in the Mouser catalog shows some 31 mix parts..
http://www.mouser.com/catalog/633/888.pdf
You can also go to Fair-rite's website and find a list of their local
distributors (Lodestone Pacific, for instance).
The 3&4 digits of the part number are the mix:
xx31yyyyyyy is a 31 mix part.
Jim Lux
> On Mon, 21 Apr 2008 10:21:36 -0400, "J. Mc Laughlin"
> <j...@power-net.net> wrote:
>
>>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.
>
>
> Hi Mac,
>
> I can't say that I have any familiarity with type 31, but certainly
> the rest and others. My reference is a 13 year old hard-copy that
> does not have this material listed, so it is hard to make side-by-side
> comparisons for like-sized beads. Looking at the other charts it
> would seem that type 31 would have less "bulk" Z (it would take more
> beads at any particular frequency to equal other formulations).
I don't know about that... the 31 material is around mu=300-800 in the
HF area, which is higher than the venerable 43, and a lot higher than
the 61.
Another advantage of the 31 material is better performance at higher
temperatures.
K9YC has written up a 50 odd page handbook on RFI suppression, choking,
etc., with a whole raft of test data on actual chokes (bead baluns,
toroids, etc.) made of various materials.
http://www.audiosystemsgroup.com/RFI-Ham.pdf
Bruce W. Ellis
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
J. Mc Laughlin
Oh my! It appears that you need a new reference. One may order a catalog
from the Fair-Rite site.
Your comment about the effect of ground is useful. However, the direction
of the coax run is such that it could enhance the vertically polarized (E
vector normal to the earth) wave received by the receiving antenna. This
might partially defeat the utility of a receiving antenna distant from noise
sources. I will test that hypothesis with NEC4.
73, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Richard Clark" <kb7...@comcast.net> wrote in message
news:2iip04hk8h3t7aobe...@4ax.com...
J. Mc Laughlin
looked at it or not, but I sure will do so.
Your material references are more recent than those of Richard. Warm
regards, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Jim Lux" <james...@jpl.nasa.gov> wrote in message
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J. Mc Laughlin
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.
Thanks also for the hints. Warm regards, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Jim Lux" <james...@jpl.nasa.gov> wrote in message
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J. Mc Laughlin
prices were on the high side, but that needs to be checked.
Warm regards, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Bruce W. Ellis" <el...@means.net> wrote in message
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J. Mc Laughlin
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Bruce W. Ellis" <el...@means.net> wrote in message
news:Ax6Pj.341$KD6...@newsfe06.lga...
>
Jim Lux
> 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)
J. Mc Laughlin
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: J...@power-net.net
"Jim Lux" <james...@jpl.nasa.gov> wrote in message
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Roy Lewallen
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
Roy Lewallen
>
> 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
Ian White GM3SEK
>
>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
Owen Duffy
news:RtydnRDA8Y1wP5HV...@bright.net:
> 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
Cecil Moore
> 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.
JIMMIE
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
JIMMIE
>
> - Show quoted text -
Apparently this testing has already been done.
Just google "type 31 ferrite" for results.
Jimmie
Jim Lux
Large, in this context, isn't all that big. You can't get it in tiny
ferrite beads to slip over a AWG30 wire. You can get it in 0.485" OD
0.5" long beads with a 0.2" hole in the middle.... $0.42 each from
Mouser. Similar snap on cases too..
Small, for Fair-rite, means things like those little 1/4" diameter multi
hole cores for making wound EMI filters, or chip components.
I buy it in 2.4" toroids so I can put multiple turns of coax on.
Jim Lux
#31 is specifically made for our kind of application (transmitting).. it
has a higher temperature rating than the other popular materials. The
key on managing dissipation is making sure you have enough impedance so
that the current is small.
It's a long way from the miscellaneous stuff used for RFI on power cords
and keyboards..
Jim Lux
Mouser has them.. Don't know if they ship in VK land or not. Shipping
of what is basically iron bars is going to be punitive. FairRite has
distribution there (Specialised Conductives in Victoria), but perhaps
not retail. But, since one typically isn't looking to buy just one, but
dozens, this might not be a problem.
One should be careful about modeling these things.. that gets you close,
but parasitics are a real bugabear. K9YC's paper has actual
measurements on actual chokes made with a variety of cores (which are
decidedly non-trivial to make..)
Snelling's book is the tome of choice, if you can find it...
Cecil Moore
> I buy it in 2.4" toroids so I can put multiple turns of coax on.
Jim, have you or anyone else you know of taken
a look at 'K' material?
Radio_Dick
group, but I had wanted to preply directly to this topic as it's very
pertinent to the discussion of ferrites, so here is the message again
(sorry if you see this twice).
Greetings All,
Saw the posts about Mix 31 ferrites, which I use on my mobile
installations with good results, using a HiQ 5/160 antenna and Icom
IC7000.
If anyone is interested, I recently posted on my web site a document
the describes the installation of ferrites for HF installations: :
www.repdesign.us ,
(go to the "Downloads" page (left side of screen towards the bottom),
and go to the third group to download or simply open to read the PDF
document).
This is based on what has worked well for me, information from Fair
Rite's web
site, and ideas from various past posings. Also listed is a partial
list of suppliers - as always check the prices as they can vary a
lot!
Check it out and let me know (direct email) if you have any other
suggestions and if you find this useful, as this is meant to be a
"continous improvement" document. I also plan to write additional
guidelines as time permits.
73,
Dick Post, N7EMW
www.repdesign.us
Owen Duffy
> Mouser has them.. Don't know if they ship in VK land or not.
Yes, but shipping anything from them and some other big suppliers is
prohibitive.
> Shipping of what is basically iron bars is going to be punitive.
> FairRite has distribution there (Specialised Conductives in Victoria),
> but perhaps not retail. But, since one typically isn't looking to buy
> just one, but dozens, this might not be a problem.
For some reason, magnetics ex USA through Aussie distributors / retailers
are outrageously expensive. Typically on Ebay one can buy 10 cores ex USA
for the price of one from a Aussie retailer.
> One should be careful about modeling these things.. that gets you
> close, but parasitics are a real bugabear. K9YC's paper has actual
Yes, agreed. I have made measurements of a number of choke
configurations, albeit only with a TAPR VNA (hate the software), and
calibrated my models to the measured values. It is certainly a balancing
act to put enough turns on a toroid to get high Z, but few enough turns
that Z hasn't gone seriously south at the top end of the desired range.
Predicting magnetics behaviour is a bit of a black art, but models help
to guide one to a better understanding of behaviour.
It is little wonder than balun specifications, where they are given, bear
little relation to the intended application.
Owen
J. Mc Laughlin
I have found the sizes of type 31 to be about the right size. On the other
hand, some of the 7X types seem only to be available in sizes that are too
small.
Your point that the type, and its performance, is only part of the issue.
One must also have parts that fit.
Thanks, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Roy Lewallen" <w7...@eznec.com> wrote in message
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Jimmie D
"Jim Lux" <james...@jpl.nasa.gov> wrote in message
news:ful734$e0i$2...@news.jpl.nasa.gov...
Interesting, I had assumed otherwise since we probably have a couple of
hundred snap on pieces we use here at work for keeping rf out of control
cables an audio lines.
Jimmie
J. Mc Laughlin
mystery to me why those who sell via the Internet do not work hard at
keeping their sites up-to-date. 73, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Ian White GM3SEK" <gm3...@ifwtech.co.uk> wrote in message
news:yaos6zEE...@ifwtech.co.uk...
J. Mc Laughlin
Fair-Rite.
Thanks for the useful observation, 73 Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Jim Lux" <james...@jpl.nasa.gov> wrote in message
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J. Mc Laughlin
another look.
73, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Roy Lewallen" <w7...@eznec.com> wrote in message
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J. Mc Laughlin
Your getting similar results with a few more 31 types than 73 types is
certainly above the noise level and reinforces the utility of 31.
Thanks. 73, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Owen Duffy" <no...@no.where> wrote in message
news:Xns9A88CAC18F...@61.9.191.5...
Jim Lux
> Dear Ian (also my father's name): Thank you for your note. It is a
> mystery to me why those who sell via the Internet do not work hard at
> keeping their sites up-to-date. 73, Mac N8TT
>
Amidon is sort of on-again/off-again when it comes to supporting the
retail ham market. Sometimes they are pretty good, but other times
they're just terrible. Might have something to do with changes in
ownership and management over the years, or just whether they get busy
with bread and butter commerical customers. They've also used a wide
variety of suppliers over the years.
And the whole Amidon, Amidon Associates, Applied Magnetics, BTC Power
Electronics, Flat Transformer Technology, thing...
It's been a long time since Bill Amidon ran it from his garage in North
Hollywood providing retail distribution for Fair-Rite and Micrometals
products.
Owen Duffy
> Dear Ian (also my father's name): Thank you for your note. It is a
> mystery to me why those who sell via the Internet do not work hard at
> keeping their sites up-to-date. 73, Mac N8TT
Mac, If you have your heart set on #31 mix, this option isn't a good
one... but if you can use #73 or #43, you will regularly see sleeves in
various sizes and materials on Ebay. Many have Fair-rite numbers so you
can check to see if they suit.
Some advertisers state that the cores are Fair-rite cores, if they know
that, they should know the part numbers though they don't always state
them in the descriptions.
I have bought ferrites from one of the suppliers, the goods seem to
comply with the part number descriptions (dimensions, mu) and their
service to Australia was quick and cheap.
In this part of the world, product from Asia is available economically...
but we have to characterise them and long term product availability is a
bit of an issue.
Owen
J. Mc Laughlin
Were I to deal with Ebay, I would have a dedicated computer and ISP just for
that purpose. I am much too much a belt and suspenders person to wish to
avail myself of their "bargains." I leave that to those who are younger.
You have reinforced my expectation that from VK land it simply might be a
necessity to deal with Ebay and to measure materials received from any
distant source.
As an extension, a new field proposed at our university is that of a
specialized engineer who is able to make the importation of parts from all
over the world work. This has become a real field. It is much worse than
the three metric systems that existed at the beginning of WW2 (American,
Canadian, and English) such that bolts might only engage a few threads
before seizing.
Your skepticism about type 31 causes me to revisit my assumptions.
As always, 73 Mac N8TT
--
J. McLaughlin; Michigan, USA
Home: J...@power-net.net
"Owen Duffy" <no...@no.where> wrote in message
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