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

[Joe Subich, W4TV]

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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>