[TowerTalk] power ratings for antennas

[Jim Lux]

I'm not sure how they develop power ratings in the first place.  As 
VE5RA commented, I'm sure it's marketing and experience, as opposed to 
formal engineering processes.  That is, I doubt anyone is building a FEM 
thermal model, or looking at convection and conduction to the 
surrounding air, analyzing the current and voltages in traps, baluns, or 
chokes, etc.

It's more a "we built an example, and we put X watts into it, and it 
seemed ok, and it seems it should take twice that, so that's what we claim."

There's also so many variables on what the power limit might be. 
Someone running 10 minutes of RTTY at 1500W is very different than 
someone doing SSB DX contesting at 1500W.

In some cases, I think, too, what you're seeing is a translation of 
power to some other parameter from construction guidelines.  I can see 
some old QST article saying "for 1000W AM, make sure you use AWG 12 
wire"...and then they wire the thing up with AWG 12 and call it "rated 
for 1kW AM"

What you're not going to see in the amateur world is specs of the 
quality used in commercial/industrial work.  For instance, at JPL, we 
use "analysis shows 10dB margin or test shows 6dB margin"  (e.g. twice 
the expected voltage and current in test).

And I'm sure someone buying high power RF systems for plasma etchers or 
broadcast systems is seeing "real" specifications with test data and/or 
analysis to back it up, if not an actual production line acceptance test 
at the rated levels.

In the amateur world, though, it tends to be more anecdotal.  "someone 
built it and it worked at least once at this level"

Which is good: it means that amateur gear is MUCH cheaper than gear with 
all the test documents and analysis.