On Wed,6/15/2016 5:32 PM, Roger (K8RI) on TT wrote:
With that set up, it worked well at 200 W, but as I increased the
power, around 1 KW (maybe a little less) every LED in the system lit
up. Instead of hanging more weight at the feed point, I added another
choke with 5 cores and 6 turns ( wound much tighter) where the
feedline reaches the tower. That completely cured the problem up to
full power out.
Hi Roger,
Look at Slide 17 in k9yc.com/7QP.pdf for a bifilar-wound choke
connected as parallel wire transmission line. This is a #31 core. The
choke design is mine, but the slick mechanical design is by Glen, W6GJB.
This choke is good for at least 600W at contesting duty cycles for CW,
SSB, and even RTTY if installed in a center-fed resonant antenna. For
greater power handling, a second choke either in the air or farther down
the line is needed. This choke CAN fry (I've done it) at high duty
cycles of legal limit CW (calling CQ after you've already worked
everyone on the band). :)
The wire is THHN, so Zo is 80-90 Ohms; antennas like the C3SS (which we
really like for portable operation) doesn't like it (I think the
mismatch screws up N6BT's coupling method), but the C3SS works fine if
you wind it with a tightly spaced pair #12 enameled wire.
We did something similar in concept with different hardware in
http://k9yc.com/80M-FDVertical.pdf See slide #26. Designing
conservatively, we used three chokes, but actual operation showed that
two was enough. Our use was with a KPA500 on CW for 7QP.
You asked about an OWA; I've lost track of what OWA is short for. :)
73, Jim K9YC
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