Hi all

I have been reading loads.

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?

And a big thank you for all the links and info.


"Ian White GM3SEK" wrote in message
...
Barett Wrote:



The Fair-Rite part number for the 2.40in #31 toroid is 2631803802. Paste
this number into the search fields at http://gb.mouser.com and
http://uk.farnell.com and search out the best deal.

[...]

I only need about 3 of them I think, so the postage is a killer
unfortunately.

I have found some FT140-43's.

Do you know if I stacked 3 Ferrite FT140-43's rings and wound 6 winding of
RG58cu through, what would the maximum impedance Ohms could I expect @
3.5MHz?


You're in luck, as I happen to have a few FT-140-43, and the measurement
equipment is out on the bench.

That 3-core choke has its best performance around 15MHz (peaking at 4000
ohms, broadband and predominantly resistive, which is quite a good result)
but at 3.5MHz it's only about 1900 ohms and mostly inductive.

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

I had only one more to add, which moved the peak down to 12MHz, 5000 ohms,
but only added a few hundred ohms at 3.5MHz.

Clearly these cores are not the best for your application.

I'm working on a better approach from the new ARRL 2010 handbook, which
uses cores that *are* available in the UK and gives the best "value for
ferrite" of anything I've seen. Publication is due in the May Radcom, but
I may be able to give some previews in the next few weeks.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Barett wrote:

I have been reading loads.

Good for you!


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?

I don't have one of those particular analysers, but be VERY careful when
measuring the high impedances that you'll typically see in RF chokes.

Most antenna analysers are primarily designed to measure impedances
around 50 ohms, and they may be quite inaccurate for impedances of
several k-ohms. Check with a 4.7k or 10k chip resistor... you may have a
nasty surprise.

Also read Jim Brown's notes about the effects of the analyser's own
shunt capacitance. Choke resonances in the HF region are the product of
several uH of inductance but only a few pF of inter-winding capacitance,
so a few pF of additional shunt capacitance from the analyser can make a
big difference. The more advanced Vector Network Analysers have the
facility to "calibrate out" such errors before making measurements, but
the AA-200 doesn't seem to have that.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

"Ian White GM3SEK" wrote in message
...
Barett wrote:

I have been reading loads.

Good for you!


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?

I don't have one of those particular analysers, but be VERY careful when
measuring the high impedances that you'll typically see in RF chokes.

Most antenna analysers are primarily designed to measure impedances around
50 ohms, and they may be quite inaccurate for impedances of several
k-ohms. Check with a 4.7k or 10k chip resistor... you may have a nasty
surprise.

Also read Jim Brown's notes about the effects of the analyser's own shunt
capacitance. Choke resonances in the HF region are the product of several
uH of inductance but only a few pF of inter-winding capacitance, so a few
pF of additional shunt capacitance from the analyser can make a big
difference. The more advanced Vector Network Analysers have the facility
to "calibrate out" such errors before making measurements, but the AA-200
doesn't seem to have that.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ok Ian all noted.

Thanks

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

"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