EMC/RFI Mains Filter

Being able to pilfer from the Ham Goodies stock can be rather convenient at times – especially when it comes to wiring-up a new Shack and deciding that a “proper” in-line mains filter should be in evidence.  GM3SEK calls these ferrites a “game changer”, so why not jump on the “Clean Shack” bandwagon?!

Making use of the well-proven 31-mix Problem-Solver snap-on ferrite core, I followed the excellent article by Adrian M0NWK after having made use of a quick “wrap-around-bodge” on an extension lead in the old PZT Shack which fed my 50-amp switch-mode PSU.  On this there were 2 cores each with 3 turns of the mains flex and I noticed a fair drop in noise on the lower HF bands (eg: 160m, 80m and 40m).

Below is the revised version which was made from stripped 2.5mm twin+earth (around 75cm length) and you’ll noticed that I had to cut 2 lengths in order to get a 3rd insulated conductor (the neutral/blue serving as the earth).

5-turns of mains cable on 31-Mix Problem-Solver Ferrite

I originally opted to place this filter straight after the consumer unit as the power enters the Shack – the sockets being on a simple “radial” circuit.  However, after some thinking, I have chosen to place it at the very end of the radial and simply feed a double socket.  This location ensures that pretty-much everything is “choked-off” before it gets to the radio’s PSU as well as the filter not having to carry whatever current other items in the Shack (and workshop) happen to be pulling.

It may be that I install another filter next to the consumer unit at a later stage – I think it’ll depend upon what QRM Generators I have in the Shack (eg: network switch, wall-warts, computers etc).  Half of the fun is the experimentation.

Mains Filter Diagram

A few terminal-blocks allow for simple connection to the mains feed and this will be placed under the desk in due course.  The usual caveats about mains voltage and licking live terminals should be applied here – I am not a Doctor.

EMC/RFI Mains Filter boxed and ready to go...

The Science Bit – have a look at M0NWK’s article for a comparison of “before and after” waterfall images from his IC-7300 based on his location/QRM situation.   This is a test that I’ll perform and update on this page once I have a bit more time and a clean workspace.

To be continued…