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Question regarding quarter wave plate impedance matching

Could some electronics guru please shed some light on this ? The input impedance looking into a quarter wave transmission line driving a load impedance ZL is: Zin = (Z0*Z0)/ZL Impedance matching literature state that ZL must be real. However, let ZL= RL + j.XL, and then the above expression can be re-written as: Zin = ((Z0*Z0)*ZL*)/((ZL*)*ZL) where ZL* is the complex conjugate of ZL. What is the flaw in this argument ? Thanks in advance for your indight.

Reply to
dakupoto
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If you have a reactive (non-real) termination on the quarter-wave line, the impedance seen at the feedpoint is also reactive.

The non-real termination can be compensated by changing the line length from 1/4 wavelength, but the transformation ratio will change.

From your title, it seems that you're thinking about a tube (valve) amplifier matching to a load. The range of mechanically available transmission line impedances is quite limited, so it may limit the plate load impedance to an impractically low value.

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-TV
Reply to
Tauno Voipio

Thanks. I was verifying some ideas -- was not tacking any impedance matching issues for the past year. No, I am not working with any tube devices.

Reply to
dakupoto

you may find the "smith chart" interesting.

m
Reply to
makolber

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