My 20 meter inverted vee dipole is fed with 56 feet of 50-ohm coax. The SWR measures 1.2 at the center of the band. According to http://arrl.org/grounding a balanced antenna doesn't need a ground, so my transceiver is not grounded. I've read that an inverted vee lowers the 73 ohm dipole impedance closer to the 50-ohm coax impedance but connecting a coax unbalances the antenna, so I wanted also to test using a current choke balun. I studied How to determine number of turns for a 1:1 balun?.
Within that post, I found How to detect common-mode currents or “RF in the shack”?. I constructed a snap-on ferrite detector with analog meter.
Without any balun, the CM meter clipped on the coax near the output of the transceiver just barely deflected when transmitting. That was encouraging but I wanted to compare it using a choke balun.
I made a choke balun on a ferrite rod 3" x 1/2" (scavenged from a Hy-Gain 1:1 balun) by wrapping a bifilar winding of 12 turns of #16 magnet wire, each winding in series with a dipole element. I inserted this balun at the antenna feed point. The SWR measured about the same as without the balun, but this time the CM meter showed about 10 times more current than without the balun.
Does that mean that the antenna doesn't need a choke balun, or the balun is not designed right, or both? Even if a wrong number of turns (I planned to test it empirically as Phil Frost suggested), I don't understand how it apparently increased the common mode current. Could my testing be bogus because the transceiver is not grounded? (I don't have a ground rod installed yet to connect). I haven't had a chance to transmit to someone but the antenna receives distant signals well so it seems correct in that respect.