On Mon, Mar 20, 2017 at 3:12 AM, Máximo EA1DDO_HK1H <ea1ddo@hotmail.com>
wrote:
> By "effective," I mean a choke that has a very high common mode
> resistive impedance at the operating frequency.
>
Indeed.
But this is THE monkey wrench in the works for a lot of folks, possibly
including the original poster on this thread. On the lower bands, a lot of
"all band" chokes have very little blocking. I've measured one as low as
173 ohms on 160 meters. Store bought devices vary all the way from cr*p to
really very well done devices designed for specific purposes from Balun
Designs, who in my mind right now is the Cadillac manufacturer of such
stuff [disclaimer: no commercial interest here].
OCF applications put a very large strain on choking devices, and really
must be done exactly right to stay away from loss. A few of us have
accumulated a collection of amusing "flaming balun" stories from around the
country, where the accumulation of heat in the enclosure eventually set all
the plastic on fire.
"Honey, there's something on fire up on your tower. And it smells bad."
For a while the North Carolina chapter of PVRC, upon provocation, would
present something called the N4AF Flaming Balun Award for various
destructive RF faux pas. You can guess the rest.
Don't be looking for a cheeep way out, or to reuse a "junk box balun" that
you can't think of any other use for, that you wish someone would tell you
it's OK to use.
Go buy something MADE FOR the application and frequency. Then string it up
and go have fun.
73, Guy K2AV
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