If the choke is primarily reactive, and the coax braid impedance is also
reactive but the opposite sign, adding the choke may *reduce* the net CM
path impedance and *increase* the braid current. Making the choke
resistive avoids that problem.
The choke resistance doesn't need to be "sky high" in this application -
it simply needs to be adequate! 1500W into a balanced 50 Ohm load means
137v worst-case across the choke. Keep the choke resistance to 2k Ohms
or more and the worst-case dissipation is a modest 9W. 2k Ohms is very
easily realised over a wide frequency range.
73,
Steve G3TXQ
On 13/05/2013 13:30, Jim Thomson wrote:
## why do they have to be resistive ?? Current squared x resistive ohms =
lotsa heat.
Current squared x XL = no heat, or minimal heat.
## If the balun is mainly resistive, it will work, but the Z has to be sky high, so
you don’t cook the
balun.
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