I would like to construct a 9:1 unun that connects my QRP transceiver to a random-wire antenna. The transceiver's antenna connection is an unbalanced BNC jack and the random-wire antenna is, well, a random wire. ;)
I have several toroidal ferrite cores laying around from disassembled power-supplies and such, but the many websites I've visited that show the construction of the 9:1 unun have not specified what type/mixture/diameter of toroidal core I need.
I'll be operating mostly on 20 and 40 meters HF.
If I were to order a toroid just for this purpose, which would be ideal for this application?
From the future -- Here is an answer that gives a lot of good information: https://ham.stackexchange.com/a/6145/1738