What sets a current balun's low frequency limit?

With a current balun, or common mode choke, what sets the lower frequency limit?

Like with this one: http://www.minicircuits.com/pdfs/TC1-1-13M.pdf, it says 4.5MHz is the lower limit but since it seems like it would pass DC I don't understand the 4.5MHz lower limit in the datasheet.

If it is just because the common mode signal blocking impedance drops down close to the value of the feed through impedance that would make since but then why on the chart does it show the return loss drops off at the lower frequency range?

Would it reflect too much signal back at the low frequencies and if so, why?

Does this mean it is unusable down to 100KHz? Still seems like it ought to pass really low frequencies to me.

Who makes a .15" x .15" common mode choke that passes 100KHz to 500MHz?

I should say, who makes one that is in a similar price range to the TC1-1-13M, S.99 per 100.

This one looks good but cost over 3x: http://www.coilcraft.com/pdfs/ja4220.pdf


thanks, George

This Balun of course can work at lower frequencies down to DC but Amplitude and Phase balance can not be maintaned at those frequencies.These are limits of a Balun that is restricted by electromechanical specifications of Ferrite core.
Look at this component.
https://www.macomtech.com/datasheets...112-CT1A40.pdf