Topband: 160m noise

[Jim Brown]

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