Choice of iron powder toriod?

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

Reply to
Jeff
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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.

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

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

Reply to
Pooh Bear

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

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Reply to
Joerg

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

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Bill W0IYH

Reply to
William E. Sabin

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Reply to
Wes Stewart

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

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Reply to
Jeff

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

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.

snipped-for-privacy@ieee.org

Reply to
LenAnderson

Hello William,

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

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Reply to
Joerg

Hello Joerg, nice to meet you for the first time.

Bill W0IYH

Reply to
William E. Sabin

Hi Guys, Results of the build and test were that the 7Mhz HPF worked very well with the "6" grade cores, but the 20Mhz LPF was crap (it used #6 as well). It started to roll off at 20Mhz as expected, dropped smoothly to -10dB by the time it got to 40Mhz, then stayed at 10dB at all frequencies above 40Mhz. I suppose the core should be a grade #10 or #12 instead of #6? or perhaps just a normal air core? JEFF

some

Reply to
Jeff

Then you haven't built the filter that you designed. The choice of core material will not affect the blow-by. If you measured the inductors at a low frequency, I would be pretty certain that you have way too much inductance at 20-40 MHz.

W4ZCB

Reply to
Harold E. Johnson

Hello Bill,

Likewise. You name sounds very familiar, IIRC from a book about design of HF gear. Didn't you work at Collins in the good old days when they had mechanical filters in their gear?

Regards, Joerg

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Reply to
Joerg

Yes. I started at Collins Radio engineering department in 1964 and retired from Rockwell Collins in 1990. For more info search Google for my name and my call sign. See QRZ.COM for W0IYH. See

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Bill W0IYH

Reply to
William E. Sabin

Did you ever work on their microwave receiver designs?

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Michael A. Terrell
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Reply to
Michael A. Terrell

Hello, Mike,

I had a little experience with some military L-band RF design (JTIDS), but that is about all. I have also designed miniature lumped-element filters for the 3 GHz region. But most of my work and also my ham radio experience have been at HF. Also, I am mostly, but not entirely, an analog specialist, which has put me somewhat into the Jurassic Age.

Bill W0IYH

Reply to
William E. Sabin

Hello Bill,

Not really. Newly minted engineers know remarkably little about analog techniques. Yet at the beginning and the end of circuits stuff usually needs to connect to the analog world. So don't be surprised when someone begs you to do just one more stint when you are past 90.

Then again a SW engineer once told me that nothing is truly analog. There is always that smallest digital step, the quantum.

Regards, Joerg

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Reply to
Joerg

There is no reason to apologize for being good with analog. ;-) I worked as a broadcast engineer during the time they announced the first memory chip, (1101) which was a slow, noisy 256 bit * 1 DRAM with very critical timing. I also did analog and digital work on the microwave equipment built at Microdyne, before L3-Com closed the Ocala plant.

The reason I asked about the microwave equipment, I would like to meet the people who designed the C-band CATV receivers I had to maintain in the '80s. I always loved Collins equipment, till I ran into those radios. They had a horrible failure rate, and took over six months to have serviced by Collins. I think I still have a set of manuals for the fixed tuned, and the agile models. I started repairing them for United Video in 1982, and could return most of them to service the same day.

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Michael A. Terrell
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Reply to
Michael A. Terrell

Hello Michael,

Seems you started with digital stuff a year or two earlier than I did. My first RAM had a whopping 1024 bits. Not bytes, bits. 21...something, I could look it up since the device where its in still works.

But their HF radios were quite reliable. Unfortunately at that time out of my budget range, and so were those nice mechanical filters :-(

Regards, Joerg

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Reply to
Joerg

2114? 1K * 4 bits?

I still have an unused 2.1 KHz Collins 455 KHz mechanical filter I bought at the Dayton hamfest years ago. Its a little narrow for voice, but it would be good for CW.

I still like Collins equipment, just not their poorly designed CATV equipment. I wish I could afford a R-390 and felt well enough to do a complete restoration. :(

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Michael A. Terrell
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Reply to
Michael A. Terrell

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