1. Tapped Tank Circuits Capacitive Tap Operation at resonance:
X1 + X2 + X3 = 0
Qu(tap) >20 (5% error)
Reactive Voltage Divider

2. Reactive Taps
Inductive tap
Autotransformer
Capacitive tap

3. Impedance Transformation
For lossless reactive components and moderate Q, a tapped tank circuit acts exactly like a transformer:
The impedance ratio is equal to the voltage ratio squared.

4. Error Analysis A rigorous analysis of the tapped tank circuit yields:
Note that the real part is given exactly by the voltage ratio (transformer) approximation, and the error term is a pure reactance, imparting a small phase shift.
Approximation
Error Term
The fractional error is:
For a given Qu, the fractional error is maximum (worst case) when a = 0, thus
If Qu = 20, the worst case fractional error is 5%.

5. Impedance Transformation
As with a transformer, the transformation is bidirectional: