2019-01-01 Loopstick Of Ferrite Suppressor Sleeves

Also to FB groups Building Transistor Radios and Ferrite Rod Antenna Experimenters

I got a bunch of ferrite RFI suppressor sleeves from goldmine-elec.com. I found a wood dowel the same size as the hole in the sleeves, and I cut it slightly shorter than the length of 5 sleeves. I drilled 1/8 inch holes in the ends and screwed #6 sheet metal screws into each end. After getting the threads formed, I screwed a rubber faucet washer onto one end, slid all five of the sleeves on, then screwed another faucet washer on the remaining end to keep all 5 snug and tight. I’m not concerned about the steel screws, I think they have very little influence on the magnetic field. But if you think it might make a difference, the sleeves could be glued on instead.

I cut off 8 feet (2.4 meters) of 24 AWG solid conductor PVC insulated telephone wire and wound it onto the sleeves, and taped it with electrical tape. I measured the inductance with my LC meter, and it measured 172 microhenrys. I wanted about 230 microhenrys, so I think that if the wire was longer, about 10 feet or three meters long, it would have been about that much inductance.

I plan on using a two section air variable capacitor with one section of 365 pF. The other section could be connected in parallel and with them in parallel with the 172 uH coil it would cover the whole AM band. I realize I could have chosen better wire, Litz wire would be best. But I don’t have any that’s heavy enough for this coil. I suppose I could use 24 AWG enameled magnet wire, and the turns would be closer together giving more inductance, but I don’t think it would be much better Q than the telephone wire. I have also thought about making some wire similar to Litz wire. I would cut four lengths of thin wire, such as 32 AWG, and twist them together enough to wind onto the core. The wire wouldn’t be as many stranded as Litz wire but it would be better than solid wire.

Update – I connected in parallel a dual section variable capacitor, both 365 pF and the oscillator sections in parallel. I can hold the coil on the AM radio next to the internal ferrite loopstick, and when I tune the variable capacitor connected to it, I can receive the station louder, with better signal strength.

2 Responses

  1. Max says:

    If it was that easy the ferrite bars whould cost little money.
    Every frequency range has its ferrite material # with different permeability. For MW is used 61 material, for longwaves is used 31 material. Those suppressor sleeves are for very low frequency around the kHz and they are probably not even ferrite but iron powder, they will not work as a ferrite core for AM antennas but there is no better way to learn it than testing.

  2. Ref your: “But if you think it might make a difference, the sleeves could be glued on instead.” ..
    – I also like the idea of a ‘screw’ for making changes (rather than glue), so a ‘non-metallic’/plastic screw seems ideal.
    – And, I understand ‘using what is on hand’ .. I do the same thing when ‘developing’ !

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