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

[Julia Tuttle]

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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[wayne burdick]

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 <[hidden email]> 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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[Rick M0LEP-2]

That'd help to explain why I was able to eke a last QSO out of a fading
battery by winding the power down (as mentioned in an article in this
February's RadCom). It was the only SOTA summit-to-summit I managed that
day, too!

Of course, next time, I'll try to remember to charge ALL my batteries
properly before setting off up to a summit, and then also put them ALL
in my pack....

On Tue 26 Jan Wayne Burdick 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.

--
73, Rick, M0LEP   (KX3 #3281)

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[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 <[hidden email]> 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 <[hidden email]>
> 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
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to [hidden email]
>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]