[Elecraft] OT: Big Ferrite Split Beads @ B.G. Micro

[Jim Brown]

On 1/20/2011 11:34 AM, Craig D. Smith wrote:
> A hint for those of you who are contemplating placing an order for some of
> the clamp-ons:  The smaller diameter clamp-ons look attractive at first
> glance due to their low prices and ability to fit most of the small cables
> in your shack.  But remember the choking impedance goes with the square of
> the number of turns.  A more expensive core with a larger aperture will be a
> much better bang-for-the-buck.  For example, a core that allows 3 turns of a
> given cable will be 9 times more effective than a single turn core and might
> only cost only 50% more.  Needing to use several single turn cores adds up
> quickly cost-wise.

Good advice. -- but there's more. RFI suppression comes from a high 
resistive impedance, which in turn occurs around the resonance of the 
choke. A single pass through a typical #31 or #43 core is resonant 
around 200 MHz -- USELESS on HF.  Multiple turns moves the resonance of 
the choke lower in frequency where we need it.   My RFI tutorial 
includes graphs of MEASURED data for some useful cores, and it also 
includes a list of ferrite cores that are most useful on the HF and VHF 
bands.  See Appendix One.   See my previous post in this thread for a 
link to the tutorial.

> I use lots of the 0431164181 clamp-ons here.

Yes,something this size is quite useful for quieting down noisy computer 
and audio gear.

73, Jim Brown K9YC