This snap-on ferrite is a serious item - It's a 31-mix ferrite that is ideal for use as a mains filter and/or HF choke for the whole of HF. With increased amounts of domestic "QRM" such as switch-mode power-supplies, televisions, cable routers and LED lighting making HF reception in some situations a non-starter - how do you go about taming it?
Known as the Problem Solver in GM3SEK's In Practice articles (and a live demo in this RSGB "Clean Up Your Shack" video) the snap-on design enables you to wind several turns of cable in a non-invasive manner. 31-mix is perfect for use across HF and especially on the lower bands - and at 3x thicker than a typical FT240-31 toroid, it's a bit of an animal!
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How to Use - For a mains choke/filter, wrap as many turns as you can around each half of the ferrite and then snap it shut. To get more turns, you can carefully remove the outer mains insulation and wrap all three wires in the same way. It is advised that you put this into a plastic box to discourage wear 'n' tear on the now more vunerable cables. As an RF coaxial choke, 8 turns should be sufficient across the HF bands. We also sell 31-mix ferrites in FT240 (2.4") diameter for Baluns, Chokes etc. Smaller 5mm snap-on and 9mm snap-on ferrites for USB cables are also available.
It's also wise to test your house without mains power - Switch-off the main circuit-breaker and run your radio off a battery: How is the noise-floor now? If it has dropped, then that's good news - it means that you can switch things back on one at a time to discover what is causing the interference. With some time and a little patience, you may get a few S-points back and possibly a much improved HF experience!
M0PZT says: "I used 2 of these with 4 turns each on the mains cable to my computer and 50-amp PSU - I noticed a 1-2 S-point drop in my noise-floor". It's harder to get rid of airborne noise, but if you have "dirty mains" then these ferrites are perfect.