[Elecraft] KPA-500 "Output for Input" schedule?

Alan Bloom n1al at sonic.net
Thu May 12 14:03:15 EDT 2011 

It may not be valid to estimate distortion based on measuring the gain
versus power level with a CW signal.  The reason is that the supply
voltage sags somewhat at maximum power, which may affect the gain.  But
that doesn't affect the distortion because the supply voltage is
(nearly) constant during a two-tone distortion test at any given power
level.

Al N1AL



On Wed, 2011-05-11 at 23:05 -0400, Guy Olinger K2AV wrote:
> Adding a power gain and rounding to nearest two digit integer,
> considering accuracy of measuring device (rarely more than two
> significant digits), it is safe to say  that the amplifier keeps its
> linearity to 650 watts.  The variability at 325 and 410 is most likely
> the measuring instrument's  issues at lower powers.
> 
> The linearity at the top PEP level is the most important, as squaring
> at that level will produce the most distortion energy.  Really quite
> good.
> 
> .............................  Power Ratio
> 
> 325W @ 15W drive   21.67  22
> 410W @ 20W drive   20.50  21
> 490W @ 25W drive   19.67  20
> 510W @ 26W drive   19.61  20
> 530W @ 27W drive   19.63  20
> 560W @ 28W drive   20.00  20
> 580W @ 29W drive   20.00  20
> 600W @ 30W drive   20.00  20
> 630W @ 31W drive   20.32  20
> 650W @ 32W drive   20.31  20
> 675W @ 35W drive   19.29  19
> 690W @ 37W drive   18.65  19
> 700W @ 40W drive   17.50  18
> 
> 
> On Wed, May 11, 2011 at 6:40 PM, Gary Gregory <garyvk4fd at gmail.com> wrote:
> > Joe,
> >
> > 325W @ 15W drive
> > 410W @ 20W drive
> > 490W @ 25W drive
> > 510W @ 26W drive
> > 530W @ 27W drive
> > 560W @ 28W drive
> > 580W @ 29W drive
> > 600W @ 30W drive
> > 630W @ 31W drive
> > 650W @ 32W drive
> > 675W @ 35W drive
> > 690W @ 37W drive
> > 700W @ 40W drive
> >
> > Is this still about right for your calculations.....
> >
> > Gary
> >
> > On 12 May 2011 08:18, Joe Subich, W4TV <lists at subich.com> wrote:
> >
> >>
> >> Adding gain calculation ...
> >>
> >>
> >>  > 2W   =  30W   11.8 dB
> >>  > 2.5W =  40W   12.0 dB
> >>  > 3w   =  50w   12.2 dB
> >>  > 3.5w =  60w   12.3 dB
> >>  > 4w   =  70w   12.4 dB
> >>  > 4.5w =  75w   12.2 dB
> >>  > 5w   =  80w   12.0 dB
> >>  > 5.5w =  90w   12.1 dB
> >>  > 6w   = 100w   12.2 dB
> >>  > 6.5w = 110w   12.3 dB
> >>  > 7w   = 120w   12.3 dB
> >>  > 7.5w = 130w   12.4 dB
> >>  > 8w   = 150w   12.7 dB
> >>  > 8.5w = 160w   12.7 dB
> >>  > 9w   = 170w   12.8 dB
> >>  > 9.5w = 180w   12.8 dB
> >>  > 10w  = 190w   12.8 dB
> >>  > 11w  = 200w   12.6 dB
> >>  > 12w  = 225w   12.7 dB
> >>
> >> The numbers look about right including the decreased gain at low level
> >> (as expected).  Using 12.6/12.7 dB would indicate 33W drive for 600W
> >> out.  40W drive for 600W output would indicate ~1 dB of compression.
> >>
> >> 73,
> >>
> >>    ... Joe, W4TV
> >>
> >> On 5/11/2011 5:28 PM, Gary Gregory wrote:
> >> > Stan,
> >> >
> >> > Allow some variation to antenna variations also.
> >> >
> >> > This on 15M, swr is 1.0:1
> >> >
> >> > 2W = 30W out
> >> > 2.5W = 40W
> >> > 3w = 50w
> >> > 3.5w = 60w
> >> > 4w = 70w
> >> > 4.5w = 75w out
> >> > 5w = 80w
> >> > 5.5w  = 90w
> >> > 6w = 100w
> >> > 6.5w = 110w
> >> > 7w = 120w
> >> > 7.5w = 130w
> >> > 8w = 150w
> >> > 8.5w = 160w
> >> > 9w = 170w
> >> > 9.5w = 180w
> >> > 10w = 190w
> >> > 11w = 200w
> >> > 12w = 225w
> >> >
> >> > NOTE to ALL: This was not done with lab equipment or even a dummy load.
> >> This
> >> > was measured  using a K3 and a tri-band yagi and a cw tone.
> >> >
> >> > Gary
> >> >
> >> > On 12 May 2011 07:13, Al Lorona<alorona at sbcglobal.net>  wrote:
> >> >
> >> >> It's very easy to measure the 1-tone gain compression characteristics of
> >> an
> >> >> amplifier. The desired result is a graph of Pout vs. Pin, with Pin on
> >> the
> >> >> horizontal axis and Pout on the vertical.
> >> >>
> >> >> So what one needs to do is set Pin to the amp, and measure Pout into a
> >> >> dummy
> >> >> load. If you do this for several values of Pin, you'll be able to plot
> >> all
> >> >> of
> >> >> those measured points on the graph. It will look like a pretty straight
> >> >> line
> >> >> toward the lower Pin values, then it will flatten out (become more
> >> >> horizontal)
> >> >> as Pin (and Pout) get higher.
> >> >>
> >> >> The slope of the line is the gain of the amplifier.
> >> >>
> >> >> Very often the Pin values are 1 dB apart. One dB is about a 25% increase
> >> in
> >> >> power. Meaning that if you are measuring Pin in Watts, then you can set
> >> Pin
> >> >> to
> >> >> roughly the following values:
> >> >>
> >> >> 1, 1.5, 2, 3, 4, 5, 7, 10, 13 Watts, etc.,
> >> >>
> >> >> and measure the Pout at each value. The values should be converted to
> >> dBm
> >> >> before
> >> >> plotting. That's all there is to it.
> >> >>
> >> >> This is all done in CW mode. If you want to go further, you can go into
> >> SSB
> >> >> mode
> >> >> and apply two tones to the amp (which a K3 has the ability to do) and
> >> then
> >> >> look
> >> >> at the output of both the K3 and the KPA500 with a spectrum analyzer...
> >> but
> >> >> I'll
> >> >> leave that explanation for another day... or it can be found on the web.
> >> >>
> >> >> Al W6LX
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> >> >
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> >
> >
> >
> > --
> >
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> > K3 #679, KPA-500 #018
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