On Sun, 11 Jan 2009 22:15:41 -0500, Paul Christensen wrote:
>Fair-Rite appears to manufacture only clamp-on cores, elongated cores, and
>large flat donut cores in #31 material.
Paul,
No, I don't see a half-inch o.d. donut toroid in #31 in the book. But perhaps
the problem is that you may have preconceived notions about what form factors
work for a given application. I've used #31 and #43 material in several
different form factors to solve audio RFI problems. ANY of those #31 parts
can be used to solve an audio RFI problem if they're big enough i.d. to get
turns through them and small enough to fit in the available space. For
example, 2631665702 is a 0.375-inch i.d., 0.687-inch o.d. cylinder that's
1.125 inch long. If you click on the part number, then click on the
"Impedance" radio button at the bottom of the page, you'll get a graph of the
Z of 1-3 turn coils. 3 turns through this part will move the resonance down
to 40 MHz with Z=1.4K at resonance.
There's also 2631625002, which is 0.312 i.d., 0.625 o.d., 0.56 long. 3 turns
gives you a resonant peak of about 1.1K at 52 MHz.
It shouldn't be too tough to interpolate from these data and my measured data
for more turns to figure out how that particular part could be used at HF. My
measured data of the "biggest clamp-on" is quite close to Fair-Rite's
published data for that part, and we measured 1-5 turns of small diameter
wire. I've also published measured data for 3-7 turns of RG8X and RG8 through
that "big clamp-on." I'd expect five turns through 2631665702 to give you at
least 4K and a resonance around 15-20 MHz.
Another point. If you're building chokes for suppression below 5 MHz, you
really want #31. If you're working at 7 MHz and above, #43 is at least as
good, and between 14 and 28 MHz, #43 is slightly better.
Our most recent group purchase bought clamp-ons and cylinders to fit both
RG8X and RG8. I've used nearly all of the clamp-ons to make multi-turn chokes
on cables in my home stereo system, to choke noisy power supplies, and so on.
The part numbers we bought are listed in that Appendix.
If you really NEED the smaller part, by all means call Fair-Rite's
applications engineering department. I've found guys to talk to who are real
engineers, not salesmen. I haven't had a lot of conversations with them, but
the ones I have had have all been excellent. You never know what they may
have built for someone as an OEM part that they can find stock of and sell
you. :)
73,
Jim K9YC
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