On Sat, 3 Mar 2007 16:41:07 -0500, "merlin-7"
wrote:

This may be a dumb question for some of you, but.....

I understand what a choke does at the feed point (I use an air wound one at
my feed point) However, I am having trouble understanding the purpose of one
near your rig.

Also what effect happens in the coax between the two chokes?

Hi Joe,

The one near your rig would be opportunistic (on the chance it was
needed). However, as it could satisfy a need then that leads us to
your second question.

The portion of the line beyond the choke at the antenna is still in a
strong field that "could" couple energy into it and reestablish the
common mode currents the choke was there to prevent. If you were to
place a second choke a quarter wave from the first, that would snub
this coupling (and thus the one at the rig, if it were harmonically
related, would also tend to snub common mode current).

I use a 20 foot line section with about 60 ferrite beads distributed
along it to make for a more multiband, or general purpose second
choke.

73's
Richard Clark, KB7QHC