rocky wrote:
You would use physically larger cores of 43 material and more turns in
the core for say 75 M in a choke balun?

Sure.

The problem actually all comes down to the common mode current flowing
through the beads, and that's the same as looking at voltage across the
shield from one end to the other of the "choke".

Some antennas, even with very low power and 50 ohm feedpoints, will
produce fairly high across the string of beads. This can cause quite a
bit of heating, and cause the feedline to remain part of the radiating
system despite the use of a balun.

In controlled situations strings of beads work pretty well. In other
cases they are totally inadequate, and the problem can have nothing to
do with the impedance across the feedline (SWR).

I never use strings of beads on my antennas.

73 Tom