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

[Wayne Burdick]

Most likely your antenna load Z was on the low side, increasing TX current drain. Either excess TX current or supply voltage below 11 V can cause power to revert to 5 watts. 

73,
Wayne
N6KR

----
http://www.elecraft.com

On Aug 5, 2013, at 5:46 PM, "Arno Dienhart" <ad at broadweave.net> wrote:

> Hi Wayne,
> 
> I measured with the built-in meter. Sorry, I don't have a dummy load, so I
> cannot test that. Next time I will connect two of the same sealed lead acid
> batteries in parallel and see if something changes. No problem to use two.
> 
> Thank you for the explanation. At least I can be sure that nothing is wrong
> with my KX3.
> 
> 73,
> Arno 
> 
> -----Original Message-----
> From: Wayne Burdick [mailto:n6kr at elecraft.com] 
> Sent: Monday, August 05, 2013 17:02
> To: Arno Dienhart
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] KX3 power reverts from 10W back to 5W
> 
> 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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> 
> 
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