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:

J. Mc Laughlin wrote:
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

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

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



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

Dear Jim: Thanks for the handbook reference. I can not remember if I have
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:
"Jim Lux" wrote in message
...
Richard Clark wrote:
On Mon, 21 Apr 2008 10:21:36 -0400, "J. Mc Laughlin"
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



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

Dear Richard:

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

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.


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.

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.

Thanks also for the hints. Warm regards, Mac N8TT

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


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.

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)

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)