[Elecraft] OT: balun rating exceeded

[Jim Brown]

On Tue, 15 May 2007 09:35:03 -0700, Ron D'Eau Claire wrote:

>The bottom line is that modern baluns are NOT designed to be used in systems
>with a wide range of impedances. 

I suggest that those interested in this thread study my tutorial on RFI
and ferrites. It includes a long section on choke baluns.

http://audiosystemsgroup.com/RFI-Ham.pdf

I am currently working on updating the "cookbook" section with improved
specific recommendations about how coaxial choke baluns must be wound
to minimize stray capacitance. I've done enough work on this to have a
good handle on what works and what doesn't, but had to interrupt it for
a biz trip to Europe. Until I've finished that and posted it, I'll
simply say that the coax should be closely spaced ONLY where it goes
through the toroids, and VERY WIDELY SPACED everywhere else.  The
difference between a coaxial choke with close spaced turns and one with
wide spaced turns is HUGE. 

For example, five CLOSE-spaced turns of RG8 through five #31 toroids
will cause a resonance (and peak performance) in the 2-3 MHz range,
while WIDE-spaced turns will yield excellent performance all the way up
to 10 meters.  

73,

Jim Brown K9YC