On 5/13/2013 5:30 AM, Jim Thomson wrote:
## why do they have to be resistive ??
Steve has given you the right answer to this.
Current squared x resistive ohms = lotsa heat.
Not if the current is small enough. And since power is current squared
but the current is inversely proportional to resistance, the power drops
twice as fast as the resistance. The key to making a resistive choke
work is to make the resistance high enough.
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.
Exactly right, except that I am specifically talking about COMMON MODE
CHOKES, which are one of many very different things described by the
word "balun." And the designs for chokes I published in 2007 provide
sufficient choking impedance at US legal limit power levels if the
antenna is reasonably well balanced. Special applications may require
more choking Z.
AND -- that high choking Z that provides sufficient power handling also
improves the decoupling of the feedline from the antenna, which improves
noise rejection and minimizes crosstalk -- which is the REAL reason for
using a serious common mode choke in the first place! W1HIS published
on this around 2006 as well.
73, Jim K9YC
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