KX2, KX3, and supply voltage vs. power output

[wayne burdick]

"Charly [hidden email] [KX3]" <[hidden email]> 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




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[Jim Brown-10]

On Tue,5/24/2016 8:23 AM, Wayne Burdick wrote:
> In CW mode, there's no issue with doing this, since it's just an unmodulated carrier.

Not true, Wayne. CW is 100% modulation of a carrier by a square wave,
the square wave includes harmonics, which produce IMD. THAT'S what
clicks are. You should know that -- your spectacularly good waveshaping
of the keying waveform in your radios is a major reason why they're so
clean on CW!  But they DO get wider when supply voltage drops, and as
power output increases, BECAUSE IMD increases.

> 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).

Yes.

73, Jim K9YC

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[wayne burdick]

On May 24, 2016, at 9:37 AM, Jim Brown <[hidden email]> wrote:

> On Tue,5/24/2016 8:23 AM, Wayne Burdick wrote:
>> In CW mode, there's no issue with doing this, since it's just an unmodulated carrier.
>
> Not true, Wayne. CW is 100% modulation of a carrier by a square wave, the square wave includes harmonics, which produce IMD. THAT'S what clicks are. You should know that -- your spectacularly good waveshaping of the keying waveform in your radios is a major reason why they're so clean on CW!  But they DO get wider when supply voltage drops, and as power output increases, BECAUSE IMD increases.

Hi Jim :)

As usually, you're theoretically correct. However, the KX2 and KX3 have such clean keying envelope shaping that when they're running 10 watts at 10 volts they're still going to be cleaner than everything else on the air (except a K3/K3S).

Wayne




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[Wes Stewart-2]

Wow two experts and they're both wrong.

Fortunately CW is neither an unmodulated carrier nor is it 100% modulation by a
square wave.  Dots with no waveform shaping would be a square wave; dashes are
never a square wave.

Keyed CW is none of the above.

On 5/24/2016 9:37 AM, Jim Brown wrote:

> On Tue,5/24/2016 8:23 AM, Wayne Burdick wrote:
>> In CW mode, there's no issue with doing this, since it's just an unmodulated
>> carrier.
>
> Not true, Wayne. CW is 100% modulation of a carrier by a square wave, the
> square wave includes harmonics, which produce IMD. THAT'S what clicks are. You
> should know that -- your spectacularly good waveshaping of the keying waveform
> in your radios is a major reason why they're so clean on CW!  But they DO get
> wider when supply voltage drops, and as power output increases, BECAUSE IMD
> increases.
>
>> 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).
>
> Yes.
>
> 73, Jim K9YC

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[Jim Brown-10]

On Tue,5/24/2016 12:56 PM, Wes wrote:
> Fortunately CW is neither an unmodulated carrier nor is it 100%
> modulation by a square wave.  Dots with no waveform shaping would be a
> square wave; dashes are never a square wave.
>
> Keyed CW is none of the above.

OK, 100% modulation of a carrier by a rectangular waveform having
variable timing. :)

It still comes down to the fact that turning on and off the carrier
creates harmonics, the rise and fall time determine their relative
strength and order. and the random timing spreads out the spectrum a bit.

73, Jim K9YC
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