I've played with ferrite toroids a little bit, building chokes & current baluns, but the doughnut shapes are a pain sometimes. I ran across some 1/2" x 2 1/2" type 61 ferrite rods for about $1.95 apiece and thought I'd give them a try.
A plus for rods is they make winding stiff solid wire a whole lot easier, but the edges aren't relieved as much as on the toroid. (Unless your winding wire has tough coat, you'd be well advised to wrap the rod first) Being an empirical type, I tried a few different wire types to see how an SWR plot would look when the winding is terminated in a 50 ohm load. So far, my best combo for a 1:1 choke has been with 14 AWG solid wire stripped out of Romex, using one bare (or enamelled) wire & one insulated wire. (see below)
The rod was wrapped with about 4 layers of teflon tape before starting. After soldering on an RG8x pigtail with PL259 on one end & a 50 ohm resistor on the other, I ran an SWR sweep with the Rigexpert AA-170. The result was a gently rising curve starting at 1.02:1 at 1.5 Mhz and not exceeding 1.29:1 through the end of the 12m band. The 10m band saw 1.30:1 at the lower bound and up to 1.32:1 at the upper end .
Nick
So far so good! The next step will be using this style of winding to build multi-core, impedance changing current baluns (guanella type) such as a 4:1 and a 9:1 to see how they look.
Nick