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
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