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Why is Load-pull actually called Load-pull

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chrisquigley82

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Hi folks,
I am curious as to whether someone could actually tell me why load-pull analysis is called load-pull. I have only seen one real statement which states that it involves "varying or 'pulling' the impedance". This statement is not fully clear as to where the word pull finds place in the analysis. If someone knows, I would appreciate if you could pass on some info on the history out of curiosity.
Regards,
Chris.
 

The terminology of load-pull appears at the time when first mechanical Slug Tuners and Line Stretchers were used for varying source and load impedances.
 

Hi vfone,
Thanks for your reply. I'm actually curious as to why they call it pulling the load. What is it that is being pulled, is what i'm actually looking for. Sorry for not clarifying this a bit more. Am just curious as to why its referred to as pulling the load impedance.
Chris.
 

The term also comes from the old Variable Frequency Oscillators (VFO's). A badly designed VFO (not enough buffering) had it's frequency pulled away from where it was initially tuned when it's loading was changed.
 

In my understanding, it's a graphic term for "pulling" maximum power out of a PA.
 

This goes back to the 1940s and magnetrons. Frequency variations caused by the power supply being off were called pushing. The ones for the load not being exactly 50 +j0 were called pulling. They had smith chart diagrams with lines of constant frequency on them.
 

The so-called Rieke diagrams are still present in today's magnetron data sheets.

In the general usage, I think "load pulling" is mostly related to load dependant output power rather than frequency variations.
It's discussed as an unwanted effect (see e.g. Cripps) as well as a technique to achieve maximum output power.
 

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