John Popelish wrote:
rocky wrote:
To sort of sum things up, then what should I use for a choke balun on
75 meters, 77, 73 or 43 mix? More the better? I read the W2DU article
and he used 73, but I thought 77 may be better?

If you are going to have to go out and buy the cores, type 43 (and its
competitors) is way more common and cheap than any of the others. It
is also readily available in long form toroids called shield beads.

You are going to get into trouble with the W2DU balun at high power
levels or with high commonn mode voltages across the balun. Each bead
suggested is only good for about 1/2 watt dissipation in open air
during long duty cycle.

Also, a string of beads is a terribly inefficient use of ferrite
materials. If you double the expense of the balun by doubling the
number of beads, you only double the common mode impedance.

If you use a less resistive material with lower loss tangent and
multiple turns through the core, you can greatly increase power
capacity and choking impedance with much less increase in cost.

73 or 75 material beads are great in 50 ohm systems at modest power on
higher frequencies when the common mode excitation is low, but I'd stay
away from that method at kilowatt power levels especially if common
mode exciting the shield is high in level or frequency is low.

For high stress applications a string of beads is terribly inefficient.

73 Tom