Amateur Radio

You have to keep in mind to not exceed coax bending radius. Solid insulator (as in not foam) coax works better. Somebody has measured them http://www.karinya.net/g3txq/chokes/

I've seen people using twisted pair of enameled wire (50 ohm) instead, or a pair of insulated twisted wires connected in parallel (each is 100 ohm impedance) this allows for much tighter turns. This works only for HF, for VHF and up there are alternatives and multiple turns don't make sense, it's better to use ferrite beads