On Sep 3, 7:18*pm, Cecil Moore wrote:
wrote:
I agree that a balun operating at 14 MHz would be a choke when
operating at 70MHz.

You would do well to agree that a well-designed W2DU balun
operating at 14 MHz is choking the heck out of the 14 MHz
common-mode current in order to achieve the balun function.

I wouldn't say it was choking the common mode.mode current, I would
say it is isolating it from diff mode current by simply creating an
isolated ground reference point (you could define it at centertap if
you were so inclined). Of course I would agree that the impedance
between diff mode current at the input and CM current in the output
had better be very high, infinity would be best, but the finite
impedances to load and source respectively should match the balun. If
you want to call the ground isolation function "choking", that use of
this colloquialism is fine with me but FYI that is not the traditional
vernacular for that that application. Also, if the W2DU balun is
referred to as the "ugly balun", I do believe the use of a bifilar
winding around an air core to create an RF transformer has been around
for more than 100 years so I do not understand why it is so-named
after a contemporary ham. It is rather simple to go from bifilar
enameled copper to using the shield and inner conductor of a coax as
"bifilar" conductors. All of this stuff is pretty basic EE (Associate
level, not even Bachelors) and I hesitate to spend much more time on
it.