Me and ham radio friend Frans PE0F ordered a considerable number of Fair-Rite toroids overseas. I can spare some, so if you need some toroids, just let me know.
FT240-43 €7, FT240-52 €10, FT140-43 or FT140-61 €4.
The 52 material is relatively new and two stacked FT240-52’s with 11 turns of RG58 seem to make the ideal wideband RF choke for 14 – 30 MHz according to G3TXQ. Also 17 turns of RG58 on a single 60mm FT240-43 makes an excellent 80/40 RF choke that’s even suitable for 160m (see measurements below).
I used to think “a couple of turns of RG58 with 4-6″ diameter (10-15 cm)” would make a good enough choke 14 MHz and up, but looking at the results below, you can see that air cored coax makes a monoband RF choke at best. So… if you need wideband RF chokes, using toroids is the way to go!