On 2/9/2010 9:32 AM, UKMonitor wrote:


Also how much impedance could I expect to gain every time I added another
FT140-43 ferrite onto the stack?


You need to double the number of beads each time to make a noticable
difference.

For worthwhile common mode suppression you need at least ten and
ideally eighty type 43 beads over a length of cable.

It's more cost effective to wind more turns. 2 x the turns 4 x the
inductance.

UKM

If I am understanding the data associated with the device (bead) you
suggested, correctly--"EMI/RFI Dämpare och ferriter Z=375 OHM @ 100
MHz", it would, indeed, take a number of them. Personally, I like to
see a Z of 10 times that of the Z of the coax. For example, for 50 ohm
coax, I would like to see a choke which would provide a "resistance" (Z)
of 5,000 ohms to any rf currents which would be tempted to ride the
braid(radiate.) While 10 of these devices may be sufficient (and would
be affected\effected by the frequencies they would be used with); I
would probably choose to use a few more.

If cost\design-needs is\are any sort of factor(s) in your design needs,
I would tend to go multiple turns on a proper core size(power handling
requirements of correct material(frequency(s) designed for.)

While ferrite may have advantages over iron cores at vhf\uhf\shf--and
become quite noticible, I have found any losses or heating tolerable at
hf and below--again, given proper core size\material--and I have used
them at much higher freqs.

The beads you mentioned are very useful though. If in a hurry, if
experimenting and time is valuable--just slap too many on the line and
go for it!

Regards,
JS

"Richard Clark" wrote in message
news
On Thu, 11 Feb 2010 11:32:35 -0000, "Barett"
wrote:

I have managed to borrow a Rigexpert AA-200. Is it possible to measure the
impedance with a AA-200 analyser and how would I do that?

Hi Barett,

Pass a single, short piece of wire through your core/bead. Connect it
to the analyzer. Read the Z. This will be enough to characterize
your ferrite material at any frequency within the range of the AA-200.
Now pass the wire (now longer) through your core/bead twice. Connect
it to the analyzer. Read the Z. You should observe four times the
earlier reading (you may have to perform complex math if the Z
contains substantial X).

Now pass the wire (now longer) through your core/bead three times.
Connect it to the analyzer. Read the Z. You should observe nine
times the earlier reading (you may have to perform complex math if the
Z contains substantial X).

Ferrite materials with one pass of wire will not exhibit a huge value
such as to lead to significant error, so as you progress through
successive passes of wire, you can be reasonably assured that the
square law will be observed within the capacity of the analyzer at low
HF frequencies (simply because the wire length being a significant
portion of a wavelength can confound measurements at higher
frequencies).

The single pass test will also help to select and compare previously
known and unknown ferrite materials.

73's
Richard Clark, KB7QHC

Nice info how to use the AA-200. Thanks

I read on the internet while reading through all the links that I should
make sure when ordering the 2631803802 #31 that they have been coated with a
hardener. Because a ferrite ring #31 that has not been treated with hardener
will break easily because the material will be too brittle.

I have been in touch with http://gb.mouser.com and http://uk.farnell.com
and they both say that there Fair-rite ring 2631803802 #31 does not come
treated with any hardener.

How important is it that they should be treated with hardener and if not
treated how easy are they to break?

Barett wrote:

Nice info how to use the AA-200. Thanks

I read on the internet while reading through all the links that I should
make sure when ordering the 2631803802 #31 that they have been coated with a
hardener. Because a ferrite ring #31 that has not been treated with hardener
will break easily because the material will be too brittle.

I have been in touch with http://gb.mouser.com and http://uk.farnell.com
and they both say that there Fair-rite ring 2631803802 #31 does not come
treated with any hardener.

How important is it that they should be treated with hardener and if not
treated how easy are they to break?


Don't worry about it. All ferrites are hard, brittle ceramics, but quite
rugged and not easily broken. They're already harder than most steels,
so I don't really believe they're ever coated with a "hardener". I've
seen them coated with an epoxy type material, but assume that's to make
them less porous and abrasive. It doesn't make them any easier to break.

Roy Lewallen, W7EL

Roy Lewallen wrote:


Don't worry about it. All ferrites are hard, brittle ceramics, but quite
rugged and not easily broken. They're already harder than most steels,
so I don't really believe they're ever coated with a "hardener". I've
seen them coated with an epoxy type material, but assume that's to make
them less porous and abrasive. It doesn't make them any easier to break.


Yes indeed.. they're hard and brittle.. Drop one of those 2.4" toroids
off a ladder onto a concrete floor, and they break.

But other than that, they appear to be pretty tough. The ones I've
gotten don't have any mold flash or lines and are smooth surfaced.

Jim Lux wrote in
:

....
Yes indeed.. they're hard and brittle.. Drop one of those 2.4" toroids
off a ladder onto a concrete floor, and they break.

Or, put two of them loose and with not protection in the post.

Actually, the easiest way I have found to chip them is to thread them on
coax for a W2DU balun, and let them fall just a couple of inches (hang on,
we are metric, that would be 50.8mm).

Owen