Constant input/output impedance variable attenuator?

neazoi

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I wonder if this small variable attenuator circuit (used for HF and below) can present a relatively constant input and output impedance, regardless of the attenuation level?
 

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As a testcase, set your attenuator to minimum attenuation. You then have input impedance 50R (left) || 50R (right) || 50R (load)
 

    neazoi

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Looking at matched T-attenuator resistor tables, you'll know that all three resistor elements have to be varied.
 

    neazoi

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{ above } > attenuator circuit (used for HF and below) can present a relatively constant input and output impedance,


If SWR is fairly tolerant, you could swap ends or oppose CW, CCW and probably get -10 to >-60 dB attenuation, then for that matter use 100 ohm pots.

But then you could any 50 ohm volume control and 50R in series out.
 
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THIS would be a lot more "constant impedance" than your first circuit:



You might want potentiometers that are more like 75 to 110 ohms....
Optimise the impedance for the nominal attenuation value you want, such as perhaps 5 dB.
 
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