Re: Rf problem

David Cutter

I've used #31 for LF coax choke following Jim Brown's recommendation which worked well but required 7 large diameter turns through 5 large cores to get the several thousand ohms suggested. Quite an expensive and bulky solution.  This was for common mode rejection in an antenna system.  To cover HF as well it required 2 chokes in series of different topology..

I'll give that a try for my next choke.  Thanks, Chris. 



On 02 May 2019 at 10:25 Chris Moulding <chrism@...> wrote:

If possible don't use a clip-on ferrite. It's better to cut the cable and fit a new mains plug after the ferrites are slipped over the cable.

The ferrite I recommend for HF RF noise suppression is the Wurth 74277290.

This was originally designed for suppression of medium wave noise affecting broadcast receivers from neon signs. It works down to 300 kHz and typically needs two or three turns through it to give a high level of suppression peaking at 2 MHz but still covering the full HF bands.

Radio amateurs rate the 31 material core for HF use but compared to a 74277290 it's like using a Polo mint!



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