[TowerTalk] Balun/Choke power ratings

[Jim Brown]

On 4/28/2014 5:40 AM, Jim Lux wrote:
> And then
> what would be a "real" objective power rating method?  Seems that one 
> of the key factors is the dissipation of whatever you're choking, 
> although if the Z is high enough, maybe that's insignificant. 

I can't think of a good one that covers all bases. My choke cookbook is 
aimed at US legal limit operation into coax-fed antennas near resonance 
that are reasonably well balanced. They are NOT designed for 
non-resonant "all band" dipoles nor off-center fed wires; these designs 
place far greater stress on a choke, and even a very good choke is 
likely to fry with high power.

A torture test that I've used is to use a choke as the end insulator of 
an end-fed vertical dipole, as described in two presentations I've done 
at various clubs and hamfests. One is in the slide show for Coax Chokes, 
the other is in the slide show about whether an HF vertical should 
roof-mounted or be on the ground. http://k9yc.com/publish.htm

Retired ARRL Antenna Book editor N6BV, is a huge fan of all-band dipoles 
fed with high impedance 2-wire line. At Pacificon last fall, Dean showed 
that if one of my choke designs were to be added at the feedpoint of a 
coax-fed half wave horizontal dipole cut for 80M, the DIFFERENTIAL 
dissipation in the choke would be several hundred watts when the antenna 
was used on 40M because of the extremely high mismatch on that band 
(standing waves). That's in addition to the dissipation due to whatever 
common mode voltage there might be across the choke.

Now, the antenna system that Dean was showing was what I call "an 
unnatural act" -- an antenna/feedline system that has a very high SWR on 
a band where it is being operated. In addition to the power that 
overheats the choke and fries it, there's a lot more loss along the 
line, so only a small fraction of the transmitter power gets to the 
antenna to be radiated.

73, Jim K9YC