[Elecraft] KX3 power reverts from 10W back to 5W

[Wayne Burdick]

Hi Arno,

The KX3 requires 11.0 volts minimum on key-down for power output levels of greater than 5 W. We do this to ensure low IMD in SSB transmit mode, but it's good practice in general because most 12-V batteries can be damaged quickly if you let the voltage go much below 11.0 with a heavy load applied.

When you measured the voltage on key-down, were you using a voltmeter at the battery, or the one in the radio? You could have been dropping some voltage across the power supply wires  (+ and - leads probably about the same), or in the KX3's DC input circuitry (reverse-polarity diode, current sense resistor, etc.). So even if you read 11.7 V, it's possible that you briefly dipped below that 11.0 threshold. 

Try running it into a dummy load, using the same battery. What is the voltage on key-down? (Make sure to bypass the ATU or tune it into the dummy load for this test.)

73,
Wayne
N6KR



On Aug 5, 2013, at 2:49 PM, Arno Dienhart <ad at broadweave.net> wrote:

> So I had set up in the park, with a charged 12V 17Ah battery connected. It
> was a hot day but I was in the shade.
> 
> 
> 
> Every time I set power level to 10W and keyed the TX, it reverted back to 5W
> instantly. Why?
> 
> 
> 
> The Volt meter showed 12.3 V at RX and dropped to 11.7V at TX. Was that the
> reason (getting below 12V)?
> 
> Was the PA getting too hot? It never went below 5W.
> 
> 
> 
> Thanks for any tips,
> 
> 
> 
> 73,
> 
> 
> 
> Arno 
> 
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