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

[Dominic Baines]

Arno,

Sure someone from Elecraft will respond with a technical 
explanation...sounds a bit like default behaviour to me and also shows 
there is a difference in the battery and the internal PA voltage and you 
are maybe close to the fold back voltage.

If the supply voltage drops below 12V (I use 7AH SLA batteries so see 
this often) then it can be lower at the PA internally (c11V + a bit) 
when it is the KX3 folds back to 5W, no real warning it just does it. I 
found it a bit annoying when I knew mine was running hot but then the 
KX3 was designed with battery /P operation in mind (I assume).  The KX3 
does the same thing to protect the KX3 if the PA gets too hot (you could 
try this, not sure it will damage the KX3 so be warned, I did this when 
I fitted a heatsink to reduce the issue... set power out to 10W, key 
down or send dah dah constantly with a keyer for a few minutes into a 
dummy load (not on air!) to make it fun do this in bright sun and watch 
the PA temp rise and rise and the rear metal panel gets hot, eventually 
the temperature will exceed what is 'safe' and the power will reduce, 
same thing happens for excess current say if a PA transistor is failing 
or an antenna impedance/VSWR changes there are multiple reasons and a 
few other situations all are designed to protect the KX3.

You could monitor the KX3 reported PA temperature and the KX3 reported 
voltage and see when it happens so you know when to adjust the power out 
level yourself or know when it is likely to happen.

I have a really nice light weight /P switch mode mains power supply it 
provides 12.2V (was for a CCTV camera) the KX3 will never exceed 8W out 
with it on CW, if you set 10W it folds back immediately to 5W.

72

Dom
M1KTA
On 05/08/13 22:49, Arno Dienhart 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