Jim,
All of the items you mention are valid in affecting the power handling
capability of the balun.
You are going to have to ask the manufacturer how they rated their product as
there are no set standard guidelines.
Other things to think about are going to be frequency, duty cycle, and SWR or
how close the match is to design intent.
Will a 3-30 MHz balun work at 1.8 or even 50 MHz? Yes but probably not at the
full rated power or at a 100% duty cycle.
I would assume that the manufacturers have rated their products in a controlled
way. So they would say that their 4:1 balun would match 200:50 ohms at 5 kW
for a 50% duty cycle within the 3-30 MHz rated frequency. Any fluctuation in
that formula like operating at 1.8 MHz, or matching 220 ohms to 50 ohms would
require derating the balun or lowering the duty cycle. Any way you look at it
you will have to ask the manufacturerer how they rated their product because I
am not aware of any global standards to which baluns are uniformly tested.
Probably wouldn't hurt to put the boots to your balun while it is still on the
ground and see if you can pick it up without leaving your fingerprints burned
to it if you are in doubt about its designed characteristics.
Earl
N8SS
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Jim
Lux
Sent: Monday, April 28, 2014 7:40 AM
To: towertalk
Subject: [TowerTalk] Balun/Choke power ratings
A recent post mentions various models of Balun or Choke with power
ratings
of, variously 3kW or 5kW.
How are those ratings derived?
Is it "run X power into a matched dummy load" and the thing doesn't
overheat
(by some TBD measure)?
Is it by computation from the breakdown voltage or current carrying
capacity
of the wires (probably without allowing for the thermal design of the
package)?
Is it "I ran a Henry 5k through it at max power into my antenna and it
seemed ok"?
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.
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