[Elecraft] K2/100 and RTTY / PSK31 duty cycles

[Bill Coleman]

I'm just starting to get into RTTY with my K2 and I'm wondering how 
much power I should use.

The KPA100 manual recommends 40 watts, with 25 watts for "higher-duty 
cycle modes such as MFSK".

Now, this statement confuses me for two reasons. First, where does 40 
watts come from? The KPA100 is rated for 100 watts of CW. Since CW has 
a 50% duty cycle, it would seem that the raw heat dissipation of the 
KPA100 should handle 50 watts of the 100% duty cycle of RTTY.

So, how do we arrive at 40 watts? Is the KPA100 less efficient when 
producing 40-50 watts than it is producing 100 watts?

Second question -- how can one have a "higher" duty cycle than 100%? 
Can someone explain how MFSK can produce more of a strain on the 
amplifier than being directly keyed down on a single tone continously?


Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901