Topband: 160m noise

[Jeff Maass]

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 at contesting.com
> [mailto:topband-bounces at 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
>