[TowerTalk] OWAs or Fans?

[Jim Brown]

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