I'm looking for input regarding the common mode (choking) impedance
for 4:1 current baluns. A friend recently purchase a commercial 4:1
current balun and, out of curiosity I set it up and measured the
common mode impedance and was very surprised at the performance I saw.
A very narrow range peaked at about 1.58 MHz. (The unit's rated
frequency range is 1-30 MHz.)

I have no experience with this type of balun having always used 1:1
ratios and I'm wondering if this is typical for this type of balun.

Because one doesn't post binary attachments on this news group I have
placed a schematic and a common mode impedance plot for the balun
along with a reference plot for a commercial 1:1 balun at;
http://k6mhe.com/balun.html

73,
Danny, K6MHE