Hi,
Im confused regarding the choice of iron powder toroid for a 7Mhz high pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice there.
Any suggestions as to the relative differences and reasons to choose between
grades 2 and 6 for the HPF in T68 size?
Thanks,
JEFF

Jeff wrote:

Hi,
Im confused regarding the choice of iron powder toroid for a 7Mhz high pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice there.
Any suggestions as to the relative differences and reasons to choose between
grades 2 and 6 for the HPF in T68 size?
Thanks,
JEFF


As far as I know, 7MHz is on the border between using one mix or the
other. You'll see different Q's because details of winding, wire choice
and mounting will affect Q, as would use of a core from another
manufacturer (I don't know if anyone other than MicroMetals uses that
system, but if they did I wouldn't count on it being standardized).

If you're not going to be hitting it with really high power and if you
don't need it to be highly resonant I wouldn't worry too much. If
you're going for an engineered solution then you should make a number of
"identical" coils and test them; just make sure that the coils you make
are representative of what you'll be manufacturing.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

In article ,
"Jeff" wrote:

Im confused regarding the choice of iron powder toroid for a 7Mhz high pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice there.
Any suggestions as to the relative differences and reasons to choose between
grades 2 and 6 for the HPF in T68 size?


Either grade 2 or 6 should work fine at 7 and 14 MHz. The Al values
differ somewhat, so the number of turns to get a given inductance will
be a little higher for grade 6 than grade 2. You only need to confirm
that the number of turns required will actually fit on your T68-size
core.

For a given number of turns, the unloaded Q does peak at one frequency
but is still quite good on either side of that frequency. Unless you
have some real need to achieve the highest possible Q for a given
inductance at the frequency of interest, I wouldn't worry too much about
it. Wind the toroids, build the filter, and see how it works out!

--
Joe

Jeff wrote:

Hi,
Im confused regarding the choice of iron powder toroid for a 7Mhz high pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice there.
Any suggestions as to the relative differences and reasons to choose between
grades 2 and 6 for the HPF in T68 size?

Having just been playing with Micrometals cores myself, I gather that -2 is
indeed the 'best' for higher frequencies.

The local distributor says it's stocked in greater depth too.

Have you also looked at Magnetics Inc and Arnold ?

Graham

Hello Jeff, wrote:

Hi,
Im confused regarding the choice of iron powder toroid for a 7Mhz high pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice there.
Any suggestions as to the relative differences and reasons to choose between
grades 2 and 6 for the HPF in T68 size?

Not that this is an exact science but typically I switch from #2 to #6
around 10MHz. But I never design with high Q because that can be a pain
in production.

Regards, Joerg

http://www.analogconsultants.com

Get a copy of Amidon's catalog which gives detailed suggestions for powdered
iron and ferrite materials, based on many years of experience.
www.amidoncorp.com

Bill W0IYH

"Jeff" wrote in message
...
Hi,
Im confused regarding the choice of iron powder toroid for a 7Mhz high
pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice
there.
Any suggestions as to the relative differences and reasons to choose
between
grades 2 and 6 for the HPF in T68 size?
Thanks,
JEFF

On Wed, 12 Oct 2005 10:47:56 +1300, "Jeff"
wrote:

Hi,
Im confused regarding the choice of iron powder toroid for a 7Mhz high pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice there.
Any suggestions as to the relative differences and reasons to choose between
grades 2 and 6 for the HPF in T68 size?
Thanks,

http://www.micrometals.com/

Thanks for all the suggestions. Ive got some Amidon T68-6 toroids to wind
up, and will test the completed filter on a spectrum analyser next week.
JEFF

"Jeff" wrote in message
...
Hi,
Im confused regarding the choice of iron powder toroid for a 7Mhz high
pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice
there.
Any suggestions as to the relative differences and reasons to choose
between
grades 2 and 6 for the HPF in T68 size?
Thanks,
JEFF

From: "Jeff" on Tues, Oct 11 2005 2:47 pm


Im confused regarding the choice of iron powder toroid for a 7Mhz high pass
filter. I need to use a small size (T68) toroid. For the freq range, some
reference texts say T68-2 is the one, others say T68-6" grade. I see
differing "best Q range" specs for the 6
grade.....2-30Mhz......10-50Mhz...etc.
Have similar need for 20Mhz LPF, but assume "6" is really the choice there.
Any suggestions as to the relative differences and reasons to choose between
grades 2 and 6 for the HPF in T68 size?

Been there, done that. In the practical case, what you can expect
is a very slight change in insertion loss in the passband, perhaps
a less sharp transition of attenuation at cutoff, depending on the
type of highpass. It can be modeled in any SPICE analysis program
with accuracy if you make a special model that adds a series R
element computed from reactance divided by Q.

For a highpass filter, the usual filter type has the inductor in
shunt. In that configuration the inductor has a reactance
directly proportional to frequency and will have little effect on
the insertion loss in the passband. The equivalent series R due to
Q won't matter much at 1/3 to 1/4 the cutoff frequency. It might
matter on attenuation in the stopband region but the analysis on
that is more difficult and a practical build-and-measure is the
quicker way to go.

For a lowpass filter, the usual configuration has inductors in
series and there the Q of the inductors will affect insertion loss
more. Those would use the lower frequency range for powder mix.

In a highpass filter it is important that the capacitors have a
minimum series inductance so that the 5x to 10x cutoff frequency
isn't disturbed. Since capacitors are usually in series, their
Q will effect the insertion loss. Fortunately, most capacitors
will have a good Q up around 500+ and won't be a factor.

Use what you have and measure the results (you've got a spectrum
analyzer handy so that's taken care of).

I made a fairly good, practical Synthesis-Analysis program for
L-C filters that includes automatic modeling of (separately) all
capacitor Qs and inductor Qs. I can attach that to private mail
if you want it. Freeware. Proven by practical test comparison.

Hello William,

Get a copy of Amidon's catalog which gives detailed suggestions for powdered
iron and ferrite materials, based on many years of experience.
www.amidoncorp.com


Absolutely. I literally wore one of those catalogs to the point where
you could see through several pages.

Then there are the ARRL Handbook and their Antenna Book. Both well worth
every penny.

Regards, Joerg

http://www.analogconsultants.com