Topband: Testing for common mode noise

[Guy Olinger K2AV]

I would also add that many times a SINGLE choke will not work and can
actually make things worse.  This is because miscellaneous capacity to
ground, or actual grounding may be already minimizing the common mode to a
degree before you add the choke.

Adding the single choke may ISOLATE the miscellaneous grounding.  Then there
is a NEW pattern to the common mode current that has a current null at the
new choke, but has a current maximum at an unfortunate place.

Adding the SECOND choke ~125 feet away from the first one puts two nulls
125' apart.

If you BEGIN your suppression planning for TWO chokes to START with, it
kills all those single choke woes before you ever get started.

If you want to do it a piece at a time, plan the TWO spots and put in the
one nearest the antennas first.

73, Guy.

On Wed, Aug 24, 2011 at 7:00 AM, Don Kirk <wd8dsb at aol.com> wrote:

>
>
>
>  Jim K9YC said :
>
>
> Second, a common mode choke does not in any way degrade
> the signal nor the performance of the antenna.
>
>  but after more offline discussions with Jim about a posting by W8JI
> warning that a improper value common mode choke can actually make things
> worse, Jim clarified his statement as follows : "My advice is based on using
> a "good" choke -- that is, based on the    data in my RFI tutorial.  For an
> RX antenna, 14-18 turns through a    single #31 toroid should be quite
> effective on 160-80M."
>
> Thanks to Jim and everyone else that responded to my posting.
>
> Don (wd8dsb)
>
>
>
>
>
> _______________________________________________
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>