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

[Guy Olinger K2AV]

I would like to know if some kind of feedback (maybe complicated)
could bring about a quantum leap in linearity, like sampling the
output of the amp and feeding that back to the K3 to digitally
pre-alter the audio to cancel the distortion going out.

On Thu, May 12, 2011 at 9:12 AM, Geoffrey Mackenzie-Kennedy
<gm4esd at btinternet.com> wrote:
> Hello Wes,
>
> The practical question "how much non-linearity is acceptable" in commercial
> HF systems has been debated by some Regulators and their advisers from
> industry for years - certainly since the early 1960s in my experience.
>
> In the context of linear amplifiers (or complete transmitters) designed for
> commercial single channel voice SSB, their linearity (or lack of) is usually
> expressed in terms of occupied bandwidth - from which the acceptable levels
> of odd order intermodulation products can be determined, which in turn leads
> to the commonly used specification limit for 3rd Order Intermodulation
> products. Even back in the 1960s the Type Approval specification limit for
> 3rd Order products was typically 30db below test tone for HF transmitters
> rated up to and including 1 kW PEP output. This spec had to be met over the
> supply voltage range as specified by the manufacturer, together when driving
> a RF load whose impedance was not only fixed at nominal (e.g. 50 +j0) but
> also at other values which escape me.
>
> For some reason this magic number of 30db appears to have remained as part
> of our ham folklore, worse yet 30db below PEP not test tone, and IMHO needs
> to be increased now that the bands are more crowded. Driving a so-so
> "linear" with a transceiver whose IMD performance is poor is a recipe of
> course for wideband crud, and there are many crud generators here in Europe.
>
> Whereas a plot of output power vs input power will give some idea of
> linearity, in particular when an amplifier enters compression, unfortunately
> it will not expose any "misbehaviour" of the level of IMD products at lower
> output levels even if the plot appears to be "linear" at these levels.
>
> To give a SSB rig a clean bill of health you really do need to perform
> two-tone tests at vaious power output levels, which I suspect Elecraft has
> done.
>
> 73,
>
> Geoff
> GM4ESD
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> ----- Original Message -----
> From: "Wes Stewart" <n7ws at yahoo.com>
> To: <elecraft at mailman.qth.net>; "G4ILOJulian" <julian.g4ilo at gmail.com>
> Sent: Wednesday, May 11, 2011 8:02 PM
> Subject: Re: [Elecraft] KPA-500 "Output for Input" schedule?
>
>
>> 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 <julian.g4ilo at gmail.com> 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.
>>>
>> ______________________________________________________________
>> 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
>
>
> --------------------------------------------------------------------------------
>
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.901 / Virus Database: 271.1.1/3632 - Release Date: 05/11/11
> 20:12:00
>
> ______________________________________________________________
> 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
>