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I was wondering if anybody could suggest some common items around the house or at the hardware store that would make a passable core for an inductor. Or items that I could salvage material from. For example, maybe bundling together a bunch of nails could work? Maybe old radios or something are a good source?

I’m trying to make a loopstick antenna, so I need a rod shaped core for that and I’d rather not just order one on the internet.

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Any AM (or AM/FM) radio built in the 1970's or later will have a loopstick antenna in it. Earlier radios will either have a loopstick antenna, or they'll have a loop antenna about as big as your hand built into the fiberboard back of the cabinet.

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I’m trying to make a loopstick antenna, so I need a rod shaped core for that and I’d rather not just order one on the internet.

Use a proper ferrite rod because it won't kill the signal like a piece of conducting iron/steel will. Consider the effects of induced eddy currents and consider that the insulation properties of a ferrite rod means that induced eddy currents will be very small. Why do you think ordinary AC transformers use insulated laminate strips of iron. Apply that thought process to the much higher frequencies used in radio communication. Don't bodge it.

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  • \$\begingroup\$ I gleefully note that for some people, the answer that is formally accepted is the one that gives them the least financial headache or the perceived easiest path. I should probably stop talking to myself. \$\endgroup\$
    – Andy aka
    Commented Dec 20, 2018 at 18:40
  • \$\begingroup\$ Oh... cancel the above comment lol \$\endgroup\$
    – Andy aka
    Commented Dec 20, 2018 at 21:33
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It might be interesting to try a bundle of clothing-hanger wire. That would have some kind of paint or varnish coating that would help with eddy-currents. However the diameter of the wire would probably allow more eddy-currents than you would like. Nothing improvised will be as good as ferrite rod. Ferrite rod could be salvaged from an old radio or television.

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That shape of appropriate material is unlikely to be available outside of something like a radio that is designed to receive AM-band radio signals. So a broken radio would be a possible source.

Here is an internet source (I have not used them) which offers a known material (Ferroxcube/Yageo 3B1) in appropriate shapes:

enter image description here

This video may also be of help.

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