250 watts INPUT of AM might produce as much as 200 watts of carrier with
modulation to 800 watts on peaks.
1 KW input AM might produce as much as 750 watts of carrier (unless the
modulated stage was a 304TL, then 850 watts was possible) and the peak
of the modulation envelope (twice voltage, four times power) would be 3
KW RF. Old high power AM hams did not appreciate the new power rules
limiting output instead of input because it meant they had to reduce
power. SSB ops liked the new power rules because 1.5 KW peak output from
a SSB linear was a lot better than 1 KW peak input which the linear kept
down to more like 600 watts.
I've found tuning a balanced line through a ferrite cored balun to be
chancy. More than once, I've tuned up and not heard well, then
disconnected the balanced feed line and the swr at the input of the
tuner didn't change. I'd tuned the balun into series resonance shorting
the feed line. The balun is far better served when it has a purely
resistive and predicted load. Recent ARRL handbooks show a T tuner with
the balun at the input and then the T circuit is left floating. Its
asymmetrical, not perfect theory for a balanced circuit, but should
perform rings around a tuner with a balun on the antenna side. Though
those that use a 4 KW balun at 100 watts have a chance of not frying the
balun, but can't avoid odd balun resonances.
Last winter I sold my dad's tuner at a hamfest. I advertised it as
suitable for QRP since the roller coil was made from 1/2" tubing and the
main tuning capacitor had at least a 3/8" air space between the plates.
Compact it wasn't. If it wasn't for the bandswitch, it could easily have
handled 5 or 7 KW.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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