Re: KPA-500 "Output for Input" schedule?

Posted by Julian, G4ILO on May 11, 2011; 7:55pm
URL: http://elecraft.85.s1.nabble.com/KPA-500-Output-for-Input-schedule-tp6352735p6353364.html

You can read the detailed description at the link I gave. In fact, it claims to have "active bias for improved SSB linearity." So it is definitely intended for SSB use.

I agree that a graph of output power vs. input power should be a straight line. But I don't believe there is a "linear amplifier" out there in the real world, particularly a solid state one, where that is actually remotely true. The practical answer may be less how much non-linearity is acceptable so much as how much linearity the state of the art is capable of within the acceptable price range.

So I think Stan WB2LQF deserved a better answer to his request for an "output for input" schedule than the statement that it was a linear relationship. If Elecraft is indeed claiming the relationship between input and output of the KPA500 is perfectly linear then let them say it. Otherwise I don't believe it.

Peter Wollan-2 wrote

Perhaps that Mirage amp is intended for FM?  Not all amps need to be linear.

     Peter W0LLN


On Wed, May 11, 2011 at 2:02 PM, Wes Stewart <[hidden email]> wrote:
> Then by definition, they aren't linear.
>
> A graph of output power vs. input power should be a straight line.  It it isn't then it's non-linear.  The practical question is how much non-linearity is acceptable.
>
> --- On Wed, 5/11/11, Julian, G4ILO <[hidden email]> wrote:
>
>>
>> If it does that then it will be the first linear amplifier
>> I have ever seen
>> that actually keeps that relationship across the whole of
>> its range.
>>
>> Most solid state amplifiers exhibit noticeable compression
>> as you increase
>> the input power, so you get a lot more than half the rated
>> power out for
>> half the specified drive power.
>>
>> Take a look at the figures for this Mirage amp (selected at
>> random as being
>> the first spec sheet I could find that proved the point.)
>> It is only truly
>> linear up to half its rated output. 10W in gives the rated
>> 160W output, but
>> 5W gives you 150W 2.5W would give you somewhere around
>> 120W. The VHF amp I
>> have here has a similar characteristic. Although it is
>> designed to be driven
>> with 5W input I am actually driving it with the K3/K144XV
>> with less than
>> half that power and still get virtually full output.
>>
>> So I think the OP actually asked a very reasonable
>> question.
>>
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