[Elecraft] Duty Cycle of FT8 #Elecraft

[Jim Brown]

On 11/10/2023 6:27 AM, Pete Smith N4ZR wrote:
> I started operating FT8 while my KPA-1500amp was out for repair.  Now 
> it's back and raising a question:
> 
> Operating with just my K-3, set at 100 watts, I would see 100 watts 
> indicated on its meter through the whole 15-second FT8 transmission.. 
> When I drive my amp, it only needs 30 watts for full CW power (on 24 
> MHz),  but the amp indicates 1200 watts input for the whole FT8 transmit 
> cycle.  I'm wondering if I should back off to protect the 
> amp,considering the duty cycle is so high - on the other hand, the 
> temperature reading profile of the amp seems to be pretty much the same 
> as on CW.

I've been told by someone who knows that 1) it is normal for MOSFet 
devices to lose efficiency as they heat; 2) the KPA1500 can run WSJT 
modes at rated power except on 6M, where it's best to not run much more 
than 1 kW for long TX sessions, like meteor scatter. It's an issue 
un-related to the the MOSFets; and 3) to use default fan settings and 
let the amp adjust upward as needed.

73, Jim K9YC