[Elecraft] K3 voltage under load

[Alan Bloom]

Very true.  There is a tradeoff between efficiency and distortion.  The
K3 has good cooling, so for a fixed station where power consumption is
not an issue, you might as well keep the PS voltage fairly high.  It
also might give you a little more power output 6 meters which tends to
run a little low.

Al N1AL


On Wed, 2009-06-03 at 23:42 -0400, Don Wilhelm wrote:
> Alan,
> 
> Your analysis is correct - BUT --
> 
> Efficiency is one thing. but it has been previously discussed that 
> higher DC voltages result in improved IMD.
> So the "best" voltage to be used is a compromise (efficiency alone is 
> not the only consideration). My preference is to stay with the 13.8 volt 
> output of my power supply and keep the voltage drop under full load to a 
> minimum by using #12 or larger conductors and low drop (APP) 
> connectors.  My vote is to stay with a "systems" approach rather than 
> concentrating on only one parameter.  YMMV.
> 
> 73,
> Don W3FPR
> 
> Alan Bloom wrote:
> > The graphs show: the lower the power supply voltage, the higher the
> > efficiency.
> >
> > The reason:  When you set the K3 to, say, 100W it has to put 1.4A into
> > the 50-ohm dummy load (P = I^2R = 1.4^2 x 50 = 100).  
> >
> > The DC current through the PA transistors is pretty much directly
> > proportional of the RF current through the transistors.  Whatever DC
> > current the PA transistors require to achieve 1.4A of RF into the load
> > doesn't depend on the power supply voltage.
> >
> > Since the transistor current is the same no matter the power supply
> > voltage, you get best efficiency (lowest power dissipation) at the
> > lowest voltage that is capable of sustaining the desired power level.
> >
> > Al N1AL
> >
> >
> > On Wed, 2009-06-03 at 19:04 -0400, Jack Smith wrote:
> >   
> >> I've made some measurements of my K3's efficiency versus DC supply 
> >> voltage, output and frequency at 
> >> http://www.cliftonlaboratories.com/elecraft_k3_efficiency.htm
> >>
> >> Jack K8ZOA
> >> www.cliftonlaboratories.com
> >>     
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html