Jim:
I regretted the use of the term "sloppy" as soon
as I hit the Enter key, but of course it was gone
by then!
I wasn't intending to disparage the use of multi-
turn chokes. What my early-morning brain was trying
to express was that there are better commonly-
available materials than #43 for the specified job
between 1.0 and 30 MHz (where most of us are
interested).
I'll defer to your experience. Given the availability
of #43, #61, #73, or #77 toroids (all of which are
commonly available), which would be your first
choice? (Fair-Rite also recommends #31, but it
does not appear to be available in toroid form).
73,
Jeff Maass K8ND
> -----Original Message-----
> From: topband-bounces@contesting.com
> [mailto:topband-bounces@contesting.com]On Behalf Of Jim Brown
> Sent: Wednesday, November 10, 2004 9:19 AM
> To: TopBand List
> Subject: RE: Topband: 160m noise
>
>
> On Tue, 9 Nov 2004 06:59:50 -0500, Jeff Maass wrote:
>
> >Isn't #43 material the *wrong* material to use for
> >supressing noise on 160 meters? It's described by
> >Fair-Rite as appropriate for 20 - 300 MHz for EMI
> >suppression. Multiple turns may make it more effective
> >at lower frequencies, but that's just sloppy.
>
> No, it's not "sloppy," it's an advanced application of the physics of
> how ferrites work, and a method of getting very effective
> suppression from commonly available components. The 20-300
> MHz recommendation assumes a single turn choke. See Fair-Rite's
> applications note on the use of ferrites for suppression, which
> includes an equation, graph, and discussion showing how multiple
> turns around a toroid will increase the impedance and reduce the
> effective frequency range of the choke by a factor roughly equal to
> the turns ratio.
>
> Now, a choke made from a material like Fair-Rite #78 would be
> more effective over a broader frequency range in the MF and HF
> spectrum with fewer turns. But the #43 material WILL work, and will
> be quite effective. More to the point -- a multiturn choke of #43 can
> provide a resistive component >800 ohms over at least an octave
> centered anywhere between about 700 kHz and 30 MHz, and the #
> 78 will cover several octaves >800 ohms over that range. The loss
> of effectiveness of the multiturn choke at higher frequencies is the
> result the interwinding capacitance.
>
> I do not speak about this from a point of conjecture -- I have done
> extensive research on the use of ferrites for MF and HF
> suppression, and plan to publish the results in the near future in the
> form of technical papers.
>
>
> Jim Brown K9YC
>
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