FT200-2 RF Toroid RF Choke
 

Hi

I'm building a Carolina Windom 80 Special. 66 feet long (25ft one side 41ft
the other with a 4:1 balun at the off centre, 10ft coax down to a RF choke.

My question is. Can I use a FT200-2 RF Toroid wound with coax to make up a
choke to use as the choke?

Thanks

FT200-2 RF Toroid RF Choke
 

"Barett" wrote in message
...
Hi

I'm building a Carolina Windom 80 Special. 66 feet long (25ft one side
41ft the other with a 4:1 balun at the off centre, 10ft coax down to a RF
choke.

My question is. Can I use a FT200-2 RF Toroid wound with coax to make up a
choke to use as the choke?

Thanks


I made a mistake in the Toriod number. It is infact a T200-A.

I have found the answer I was looking for on a web site. See belowe. It
might help some one else with the same ideas of using this a choke.

My recommendation is to pick a different material. T-200-2 is a powered iron
material; the permeability is way too low to build an effective
coaxial-cable choke with. The AL value is 120 (meaning it takes 120 turns to
make a 100 uH choke).

You should be looking at ferrite, probably mix 31, 43, or 61. Mix 31
requires the fewest turns.

I have another question.

What is the T200-2 Toriod used for and why is it good for that purpose?

Thanks

FT200-2 RF Toroid RF Choke
 

On Feb 9, 8:40*am, "Barett" wrote:
"Barett" wrote in message



I have another question.

What is the T200-2 Toriod used for and why is it good for that purpose?

Tuned circuits e.g. antenna matching & filters, that's about it !

#6 is even worse for HF broadband transformers

Too many folks use iron powder cores of all types for totally
unsuitable purposes.

UKM

FT200-2 RF Toroid RF Choke
 

"UKMonitor" wrote in message
...
On Feb 9, 8:40 am, "Barett" wrote:
"Barett" wrote in message



I have another question.

What is the T200-2 Toriod used for and why is it good for that purpose?

Tuned circuits e.g. antenna matching & filters, that's about it !

#6 is even worse for HF broadband transformers

Too many folks use iron powder cores of all types for totally
unsuitable purposes.

UKM

Does any one know where I can purchase some Ferrite rings type 31 material
from in the UK?

and thanks to UKM.

FT200-2 RF Toroid RF Choke
 

Barett wrote:

What is the T200-2 Toriod used for and why is it good for that purpose?

Tuned circuits e.g. antenna matching & filters, that's about it !

#6 is even worse for HF broadband transformers

Too many folks use iron powder cores of all types for totally
unsuitable purposes.

UKM

Does any one know where I can purchase some Ferrite rings type 31
material from in the UK?

and thanks to UKM.


UKM is right: iron powder material is not suitable for RF chokes.

Well done for finding out about Fair-Rite 31 material - you must have
been reading Jim Brown K9YC's tutorials on www.audiosystemsgroup.com
:-)

None of the UK amateur suppliers seems interested in stock large toroids
or beads in this material (and believe me, I have tried) so the next
best thing is to order from the USA.

As Jim Brown has often advised, order directly from an industrial
supplier in the USA, and not one of the "amateur" suppliers. When
ordering from outside the USA, the most cost-effective route is probably
either Mouser or Farnell because they handle the international shipping
and Customs clearance, so you don't get hit for the same one-off charges
and 'collection fees' that a personal import would.

There is no import duty on these electronic parts, but of course you
still have to pay 17.5% VAT on the whole bill.

The best value will depend on the size of your order, and of course on
any special offers, but it's sure to be cheaper than any of the US
amateur suppliers like Amidon. Mouser have a free Fedex shipping deal on
orders above GBP50. Farnell can supply US stock from their Newark
Electronics affiliate with an extra charge of GBP15 per order (they
removed this charge for the whole of January, and maybe this offer might
be repeated).

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.

Ah, too bad... Mouser currently have an 11 week lead time.

Farnell have 95 of them at Newark Electronics. (Ignore the wrong
information about "43 shield beads". Farnell/Newark confirmed that the
cores really are #31, but it may take some time to correct the web
page.)

Also worth considering is the giant #31 clamp-on bead 0431177081... an
exercise for the reader.



--

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

FT200-2 RF Toroid RF Choke
 

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

What is the T200-2 Toriod used for and why is it good for that purpose?

Tuned circuits e.g. antenna matching & filters, that's about it !

#6 is even worse for HF broadband transformers

Too many folks use iron powder cores of all types for totally unsuitable
purposes.

UKM

Does any one know where I can purchase some Ferrite rings type 31 material
from in the UK?

and thanks to UKM.


UKM is right: iron powder material is not suitable for RF chokes.

Well done for finding out about Fair-Rite 31 material - you must have been
reading Jim Brown K9YC's tutorials on www.audiosystemsgroup.com :-)

None of the UK amateur suppliers seems interested in stock large toroids
or beads in this material (and believe me, I have tried) so the next best
thing is to order from the USA.

As Jim Brown has often advised, order directly from an industrial supplier
in the USA, and not one of the "amateur" suppliers. When ordering from
outside the USA, the most cost-effective route is probably either Mouser
or Farnell because they handle the international shipping and Customs
clearance, so you don't get hit for the same one-off charges and
'collection fees' that a personal import would.

There is no import duty on these electronic parts, but of course you still
have to pay 17.5% VAT on the whole bill.

The best value will depend on the size of your order, and of course on any
special offers, but it's sure to be cheaper than any of the US amateur
suppliers like Amidon. Mouser have a free Fedex shipping deal on orders
above GBP50. Farnell can supply US stock from their Newark Electronics
affiliate with an extra charge of GBP15 per order (they removed this
charge for the whole of January, and maybe this offer might be repeated).

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.

Ah, too bad... Mouser currently have an 11 week lead time.

Farnell have 95 of them at Newark Electronics. (Ignore the wrong
information about "43 shield beads". Farnell/Newark confirmed that the
cores really are #31, but it may take some time to correct the web page.)

Also worth considering is the giant #31 clamp-on bead 0431177081... an
exercise for the reader.



--

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

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?

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

Thanks for you links and info.

FT200-2 RF Toroid RF Choke
 

On Feb 9, 3:33*pm, "Barett" wrote:
"Ian White GM3SEK" wrote in ...





Barett wrote:

What is the T200-2 Toriod used for and why is it good for that purpose?

Tuned circuits *e.g. antenna matching & filters, that's about it !

#6 is even worse for HF broadband transformers

Too many folks use iron powder cores of all types for totally unsuitable
purposes.

UKM

Does any one know where I can purchase some Ferrite rings type 31 material
from in the UK?

and thanks to UKM.

UKM is right: iron powder material is not suitable for RF chokes.

Well done for finding out about Fair-Rite 31 material - you must have been
reading Jim Brown K9YC's tutorials onwww.audiosystemsgroup.com:-)

None of the UK amateur suppliers seems interested in stock large toroids
or beads in this material (and believe me, I have tried) so the next best
thing is to order from the USA.

As Jim Brown has often advised, order directly from an industrial supplier
in the USA, and not one of the "amateur" suppliers. When ordering from
outside the USA, the most cost-effective route is probably either Mouser
or Farnell because they handle the international shipping and Customs
clearance, so you don't get hit for the same one-off charges and
'collection fees' that a personal import would.

There is no import duty on these electronic parts, but of course you still
have to pay 17.5% VAT on the whole bill.

The best value will depend on the size of your order, and of course on any
special offers, but it's sure to be cheaper than any of the US amateur
suppliers like Amidon. Mouser have a free Fedex shipping deal on orders
above GBP50. Farnell can supply US stock from their Newark Electronics
affiliate with an extra charge of GBP15 per order (they removed this
charge for the whole of January, and maybe this offer might be repeated).

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

Ah, too bad... Mouser currently have an 11 week lead time.

Farnell have 95 of them at Newark Electronics. (Ignore the wrong
information about "43 shield beads". Farnell/Newark *confirmed that the
cores really are #31, but it may take some time to correct the web page..)

Also worth considering is the giant #31 clamp-on bead 0431177081... an
exercise for the reader.

--

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

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?

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

Thanks for you links and info.- Hide quoted text -

- Show quoted text -

Take a look at

http://www.karinya.net/g3txq/chokes/

http://audiosystemsgroup.com/RFI-Ham.pdf

http://www.yccc.org/Articles/W1HIS/C...S2006Apr06.pdf

Mouser and Newark are you only real options, watch out for special
shipping offers and take advantage of them when they occur.

The giant #31 clamp-on beads 0431177081 are expensive but equivalent
to three 240 sized rings.

UKM

FT200-2 RF Toroid RF Choke
 

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

FT200-2 RF Toroid RF Choke
 

For the 4:1 Ruthroff balun Type 43 or 31 is not ideal for this
purpose, use approx 12 bifilar turns on a FT240-61 core.

Wind the transformer with twin figure of eight speaker cable which is
OK for low power up to about 100w. Use thin 100 ohm twin feeder sold
by Spectrum Communications for higher power levels.

UKM

FT200-2 RF Toroid RF Choke
 

On Tue, 9 Feb 2010 15:33:57 -0000, "Barett"
wrote:

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

Hi OM,

Z varies by the square of turns THROUGH the center (turns are always
integers, not fractions). Z is a function of formulation (the mix of
the ferrite) which defines the optimum band(s) of operation. Z is
also a function of mass, but it doesn't take much, a small bead that
comfortably girdles RG58 will present several 10s of Ohms Z. Z is a
function of frequency, but most ferrites exhibit very mild shifts in Z
as frequency changes. You can chain beads or toroids to build up your
Z. You typically want your choke at least 3X the Z of the feedpoint -
10X is very much more preferred.

As for resources and cost, go to your nearest computer monitor
recycler and obtain any deflection coils that may still be around in
this era of flat screens. They have been reportedly quite useful.

If you do this, you will have to characterize the formulation of the
available ferrite through experimentation. If you have an antenna
computerized analyzer, you can measure this directly. If not, this
may take invention and thought (and more posts here).

73's
Richard Clark, KB7QHC

FT200-2 RF Toroid RF Choke
 

"Barett" wrote in
:

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

We experience the same problem here in VK. Local resellers charge very
high prices, and many US suppliers charge very high shipping on
magnetics.

Another option is to look on Ebay, Ebay sellers who really want to sell
internationally have reasonable prices... but be prepared for excessive
shipping quotes from some.


I have found some FT140-43's.

You could use these to make a common mode choke, but the physical size
limits the amount of heat that they can dissipate and the power rating.


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?

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

At low frequency, the impedance is close to proportional to the square of
turns, and proportional to the number of cores stacked but for a core of
this type, the inductor will probably be self resonant in the HF range
and stacking cores increases self capacitance and reduces the self
resonant frequency and the above approximation does not apply so well.

I should stress that self resonance isn't necessarily bad for these types
of lossy inductors, you should put aside Rules of Thumb (ROT) that say to
never use an inductor above its self resonant frequency.

I have written a short article entitled "A method for estimating the
impedance of a ferrite cored toroidal inductor at RF" which you may find
interesting, it is at http://vk1od.net/blog/?p=806 .

Is Neosid still selling product in the UK? I believe they stopped
manufacture, but they may be selling product.

In answer to the shipping cost issue, I went looking for a locally
available core that suited a general purpose HF common mode choke, and
Neoside produce a core larger than FT240 with a material that is a good
choice for the purpose, similar to Fair-rite #52. I describe the design
at http://vk1od.net/blog/?p=581 . Moving house has delayed completion of
this, the design is done, the materials are here, I just have to
construct one in a box and measure its common mode impedance to calibrate
the amount of equivalent shunt capacitance. An alternative would be a
stack of two FT240-52 cores.

Everybody, and every manufacturer has a recipe for common mode chokes,
but if you do not provide a plot of common mode impedance, preferably R
and X separately, then you might reasonably question the recipe.

None so more than the commercial purveyors of the magic Caronlina Windom
which calls out aspects many of us might regard as a disadvantages as
positive features (sheer marketing spin) and depends on undescribed
proprietary components.

Owen

FT200-2 RF Toroid RF Choke
 

Owen Duffy wrote in
:

....
Everybody, and every manufacturer has a recipe for common mode chokes,
but if you do not provide a plot of common mode impedance, preferably
R and X separately, then you might reasonably question the recipe.

Aargh!

Everybody, and every manufacturer has a recipe for common mode chokes, but
if *they* do not provide a plot of common mode impedance, preferably R and
X separately, then you might reasonably question the recipe.

FT200-2 RF Toroid RF Choke
 

In article ,
Barett wrote:

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?

I did something like that a few years ago, to build a common-mode
choke for our ARES/RACES ham shack's HF feedline.

I used off-the-shelf (surplus-store) ferrite tubes - very probably a
43 mix or something close to it, based on the simple inductance
measurements I did with an MFJ analyzer. They're roughly 1 inch long,
and large enough to allow three through-the-center passes of RG-8X coax.

I glued somewhere around six of them, end-to-end, to create a long
tube, and then ran the RG-8X through... creating a long three-turn
choke. Added N connectors to the ends of the coax and stuffed the
whole thing into a chunk of PVC tube with end-caps.

The results were gratifying. When I tried a common-mode measurement -
along the braid, from one end connector to the other - the impedance
at 3.5 MHz was too high for the MFJ meter to read it... it simply said
" 1500".

A normal (differential-mode) measurement through the coax, looking
into a 50-ohm dummy load, reads 50 ohms (1:1 SWR) as closely as
matters not (i.e. within the accuracy of the MFJ meter).

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

FT200-2 RF Toroid RF Choke
 

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

FT200-2 RF Toroid RF Choke
 

Dave Platt wrote:

I used off-the-shelf (surplus-store) ferrite tubes - very probably a
43 mix or something close to it, based on the simple inductance
measurements I did with an MFJ analyzer. They're roughly 1 inch long,
and large enough to allow three through-the-center passes of RG-8X coax.

I glued somewhere around six of them, end-to-end, to create a long
tube, and then ran the RG-8X through... creating a long three-turn
choke. Added N connectors to the ends of the coax and stuffed the
whole thing into a chunk of PVC tube with end-caps.


You might do better breaking the thing up into multiple cores and
multiple windings. That is, rather than 3 turns through 6 cores, do 3
turns through 1 core, then 3 turns through another core, then 3 turns, etc.

The logic here is that the impedance scales as the number of cores, but
doing them all in one shot means that the input coax is very close to
the output coax, so you have a lot more capacitance coupling the input
to the output.

I think Jim K9YC actually did some comparisons using #31 2.4" cores
comparing stacking to stringing em out.

FT200-2 RF Toroid RF Choke
 

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

FT200-2 RF Toroid RF Choke
 

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

FT200-2 RF Toroid RF Choke
 

"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

FT200-2 RF Toroid RF Choke
 

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

FT200-2 RF Toroid RF Choke
 

On Feb 9, 2:24*pm, Jim Lux wrote:
Dave Platt wrote:
I used off-the-shelf (surplus-store) ferrite tubes - very probably a
43 mix or something close to it, based on the simple inductance
measurements I did with an MFJ analyzer. *They're roughly 1 inch long,
and large enough to allow three through-the-center passes of RG-8X coax..

I glued somewhere around six of them, end-to-end, to create a long
tube, and then ran the RG-8X through... creating a long three-turn
choke. *Added N connectors to the ends of the coax and stuffed the
whole thing into a chunk of PVC tube with end-caps.

You might do better breaking the thing up into multiple cores and
multiple windings. *That is, rather than 3 turns through 6 cores, do 3
turns through 1 core, then 3 turns through another core, then 3 turns, etc.

The logic here is that the impedance scales as the number of cores, but
doing them all in one shot means that the input coax is very close to
the output coax, so you have a lot more capacitance coupling the input
to the output.

I think Jim K9YC actually did some comparisons using #31 2.4" cores
comparing stacking to stringing em out.

Jim's comment is a good one from another standpoint he didn't mention
explicitly too: if you put a single choke right at the antenna
feedpoint, and the feedline is in some sense resonant (e.g. a quarter-
wave long with the far end grounded), the fields from the antenna may
very well excite currents on the outside of the feedline anyway, even
with a "perfect" choke. By putting the separate chokes spaced out
along the line, say a quarter-wave apart at the highest operating
frequency, you break up resonances that might otherwise occur in the
line.

By the way, for a single-band choke on a band (10 meters) that was
extremely troublesome for me in one installation many years ago, I
wound (approx., from memory) 5 turns of the feedline coax into a
solenoid coil about 12cm diameter, secured so they were stable. That
made a coil of roughly 3 microhenries inductance, self-resonant just a
bit above 30MHz. A pure 3uH would only be a little over 500 ohms
reactance, but resonated with a wee bit of capacitance across the
coil, the result was a very high impedance that solved the problem
nicely. I've since found the technique valuable and easy to apply to
RG-58C/U type line used at 147MHz--much smaller coils, secured on
sections of PVC water pipe.

Cheers,
Tom

FT200-2 RF Toroid RF Choke
 

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

FT200-2 RF Toroid RF Choke
 

"Richard Clark" wrote in message
...
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?

FT200-2 RF Toroid RF Choke
 

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

FT200-2 RF Toroid RF Choke
 

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.

FT200-2 RF Toroid RF Choke
 

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