Topband: Rolling your own FCP isolation transformer, IMPORTANT.

[Guy Olinger K2AV]

Due to email conversations with a surprising number of folks not quite
getting the "isolation transformer" part right, we have made some
adjustments to the drawings on http://www.w0uce.net/K2AVantennas.html .

Whether due to accidentally "flipping" the connection on one end of the
winding, or simply misunderstanding directions or function, thereby some
have turned their home-brew winding from an isolation transformer into a
weak choke balun wound on a powdered iron core, especially weak on 160.  By
doing so, they have allowed the counterpole to choose between the FCP and
their coax shield, now the low Z choice, and route the bulk of their
counterpole power onto what amounts to single miscellaneous "radial" on the
ground.  And thereby in the bargain, they have thrown the FCP improvements
out the window.

When you get done building it, take an ohmmeter, and for illustration
assuming you are using an SO239 connector for the coax and post insulators
for connections to FCP and vertical conductor, MAKE SURE that you do NOT
get a short between the shell of the coax jack and either post going to the
FCP and vertical conductor, or between the center conductor and either
post.  To finish the check, you SHOULD get a short between the two posts.
 You SHOULD get a short between the shell and center conductor of the coax
jack.

Repeat, getting that wrong can throw all the benefits out the window.  The
tricky part is that if you do get that wrong, it still passes power to the
antenna when it's wound wrong, and may seem like it's working until you
start comparing Reverse Beacon Network readings.

If you put one up and you're not sure, go check it out.

73, Guy.