Re: [WriteLog] RFI

["Ian White, G3SEK" <G3SEK@ifwtech.co.uk>]

Barry Merrill wrote:
> I completely disagree with your claim:
>
> "The ferrite chokes ARE a good idea, but not necessarily on the network cables.
> For HF, you need a lot of turns around one of the bigger toroids commonly
> used for baluns (#43 material). The clamp-on chokes won't do much below VHF."
>
>
> As I've reported numerous times, the sole source of cw keying lockup
> with Writelog and PC generated CW in my second story radio shack was
> the LAN cable to the ThinkPad, and five snap-on ferrites on the LAN
> cable at the Thinkpad eliminated the rfi.
>
> specifically, http://www.surplussales.com/FerSplit-1.html
>
>  (currently $6.95 per pair of the 1/2 inch),
>  "All made with 43 material, effective DC-200 MHz".
>
>
> RFI hit the computer at about 275 watts output from the Alpha;
> each snap-on ferrite I added raised the threshold of rfi by
> about 300 watts before lockup, so with five I can run full
> 1500 watt output.

These two contradictory experiences show what we all know about RFI - 
every situation is different.

Barry was probably fortunate to have a "soft target" problem that could 
be cured by a few snap-on beads; but there may be many other, harder, 
cases where Jim would be right about needing several turns on a much 
larger core.

Keep an open mind.

One of the best tools for solving RFI problems is a clip-on RF current 
meter - details on my website. It lets you *see* where the RF currents 
are going, and how effective your ferrites etc are in stopping them.



--
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                           Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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