What are ferrite rings? What are they for? What do they do?

The last thing any of us want is to cause interference to our neighbours. However, it does happen. OK, so it’s not always our fault. If your neighbour has some crappy TV and is picking up your signal, then it may well be the fault of his TV. Of course, you can’t tell him that. Well, you can. But it wouldn’t do much for neighbourly relations. By the way, it’s not always best to fiddle about with his TV. If it goes wrong a week or so later, I can just hear him saying... It was all right before you touched it!

Before talking about ferrite rings, it’s worth mentioning ferrite rods and their use in eliminating interference. The diagram on the left shows a ferrite rod with mains lead wrapped around it. Ferrite rod aerials from old transistor radios are ideal for this purpose. The mains lead from your TV not only picks up RF from your transmitter, but radiates time base interference. This is most prominent on the lower frequency bands such as 160 and 80 metres. By wrapping the lead around a ferrite rod, as close to the TV as possible, most if not all the interference can be eliminated. Wrap the lead tightly around the rod and use PVC tape to hold it in place. It might be an idea to do the same to the video recorder mains lead.

The wire around the ferrite acts as a choke for RF currents and time base noise. A ferrite ring or rod provides a large inductive reactance at the insertion point, similar to an RF choke. I have ferrite rods and rings all around the house. Telephone wires, speaker wires, computer cables... You name it, I’ve choked it with ferrite. Remember to place the ferrite rods or rings as close to the equipment as possible to prevent RF getting into, or interference getting out of, the TV or whatever.