Having resolved which ferrites to use for 200:50 ohm transformers it is time to see if any of the cores I have are suitable for matching from 50Ω to a lower impedance using a bifilar winding. The application in mind is for the input stage matching on a single ended mono band HF amplifier delivering 10W or more.
While I have built push pull HF amplifiers it always struck me as ironic that semiconductor manufacturers often specify the IMD properties of RF transistors in a single ended circuit. However, that just gets ignored because push-pull configurations are claimed to deliver lower distortion and harmonic cancellation. Maybe that's possible, but I know single ended amplifiers can deliver very good results. And I struggle with the concept that a transistor in the off state can cancel harmonic energy generated by a transistor in the on state. Perhaps the overall result is less about the topology and more about the implementation?
My approach will be to determine which core can offer a good transformation from 50 to 12.5 ohms, then use two back to back to see what the loss is and how well the core copes with 1W of RF.
73's
Richard
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