[Elecraft] [KX3] Why more power-efficient at or below 3 W?

[Julia Tuttle]

Okay, but sometimes the changeover point is 5 watts instead of 3 -- what's
going on in those cases?

Cheers,

Julie

On Tue, Jan 26, 2021 at 2:32 PM Wayne Burdick <n6kr at elecraft.com> wrote:

> There are two windings on the PA output transformer: 1:1 and 1:4. We
> select one of these based on power level, battery voltage, and in some
> cases, operating mode.
>
> In the 1:1 setting, the PA drain impedance is 50 ohms, making it more
> efficient for at power levels, reducing current drain.
>
> In the 1:4 setting, the PA drain impedance is 12.5 ohms; the transformer
> steps it back up to 50 ohms for the low-pass filters. In this case it's
> more efficient at higher power levels, at the expense of higher current
> drain.
>
> Wayne
> N6KR
>
>
>
> > On Jan 26, 2021, at 11:07 AM, Julia Tuttle <julia at juliatuttle.net>
> wrote:
> >
> > The manual states in a couple spots that the KX3 can transmit more
> > power-efficiently when output power is at or below 3 Watts.
> >
> > Why is this? Is there an (additional?) amplifier stage that is bypassed
> at
> > these lower power levels?
> >
> > Thanks,
> >
> > Julie
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