Economics,
and the variability of the mismatch or the perception of that is why more
protective features are not built in!
If you save even 5 cents on a resistor, or if you had to spend a $2 on a 25
watt resistor, that is a big issue with low profit ham equipment. As you
point out, for a full range of powers you might need a more expensive resistor
for its voltage breakover rating.
If truth be told, most tuners on the market today are copies of other Tee
tuners, and if the first designer did not do it, then the later ones don't
either. Just human nature to follow the pack. Management and marketing often
call the shots, not engineering dept.
I believe the variation might not be more than that represented by a 3:1 SWR
on the input side of the antenna matching unit, and thus easily done with a
carbon resistor. But another factor today is the Carbon composition in 1 and
2 watt sizes for highest voltages is not as common as in tube days, and thus a
cost item. Wire wounds are a magnitude more expensive, but are good
candidates.
The other thing we see with scientific instrumentation all the time. The
designer thinks he will shave a buck and let the source or load designer put
in the needed protection!
There is the old joke about a project would never finish, if the engineers got
to put in every possible bell and whistle that would be desirable. More truth
than fancy there too.
73, Stuart K5KVH
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