[Elecraft] KX2, KX3, and supply voltage vs. power output

[Wayne Burdick]

"Charly w6cup at hotmail.com [KX3]" <KX3-noreply at yahoogroups.com> wrote:

> 
> Regarding 10 watt operation with the KX2, I read operation on only 5 watts is recommended with internal 2.6 amp battery because of intermodulation ---but later I Read 10 watts is Ok-- Of course with xternal battery with higher voltage is ok with 10 watts -- which is it?? Charly W6CUP -- soon to be a very lucky owner of a KX2--


Hi Charly,

Firmware in both the KX2 and KX3 will allow power output of up to 10 watts down to as low as 10 volts key-down. This is not a guaranteed level, but most of the radios will hit this level on most bands.

In CW mode, there's no issue with doing this, since it's just an unmodulated carrier. 

In voice and data modes, we strongly recommend using higher voltages at full power output. This will result in much better suppression of IMD products (unwanted higher-order sidebands). 

(Like all other "12 volt" transceivers, the KX3 and KX2 are tested and characterized for IMD using a supply voltage of about 13.8 volts. This applies to both manufacturers and test organizations like the ARRL.)

That said, *when necessary* you may want to run higher power in voice/data modes at lower voltage. "When necessary" always applies in an emergency situation, but in other cases this is a gray area left to the operator. 

For example, imagine you're standing on the edge of the Grand Canyon, holding your KX2 HT-style, when you hear South Dakota for the first time in your life, on 17 meter USB. You must work the station *now* or resolve to end your misery by plunging into the canyon, whip-first. 

He doesn't hear you when you call using 5 watts. So you check your supply voltage (using the DISP function) and see that your internal Li-ion battery is a solid 11.0 volts.

Is this an "emergency" that calls for the temporary use of a full 10 watts, risking slightly higher IMD that at QRP levels will neither cause QRM nor harm small animals? Your call :)

I suppose we could put all of this into the Specifications page of the manual.

73,
Wayne
N6KR