[Elecraft] K1 Power Out vs. Current Draw

[Paul Kirley]

Wayne N6KR has addressed the matter of K1 transmit efficiency in his
note at
http://www.elecraft.com/TechNotes/k1_battery_op.htm

Wayne's formula shows the most efficient power setting as a function of
supply voltage.  It's easy to remember:  square the supply voltage and
divide by 25.

Basically, impedances need to be matched at DC in for greatest DC
efficiency, just as they do at RF out for greatest RF efficiency.  

As the battery voltage decreases, the optimal K1 power setting will
also decrease, but quadratically--not linearly.

The voltage that should be used in the calculations is that displayed
by the K1, that is, after reduction for the loss in the
polarity-protection diode.

73, Paul W8TM