Use of type 31 ferrite as coax common mode choke
 

Dear Owen: Stray capacitance due to more than one source has a big effect.
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:
"Owen Duffy" wrote in message
...
"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

Amidon Use of type 31 ferrite as coax common mode choke
 

J. Mc Laughlin wrote:
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.

Use of type 31 ferrite as coax common mode choke
 

"J. Mc Laughlin" wrote in
:

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

Use of type 31 ferrite as coax common mode choke
 

Dear Owen: Always good to receive your insight.

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:
"Owen Duffy" wrote in message
...
"J. Mc Laughlin" wrote in
:

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