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.
How to Use - For a mains choke/filter, see the picture above - it uses the conductors of 2.5mm twin&earth with 5 turns in total and is best used for your radio's PSU only so that anything else is behind the filter. 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!