Tuned Circuit Bandwidth

To calculate the bandwidth of a tuned circuit, a graph of impedance (Z) against frequency (f) is usually used.

1. Determine from the graph, the maximum impedance at resonance, which in the example graph, is the green line from the peak.
2. Then calculate 70.7 % of the maximum impedance.
3. Draw this value on the graph, which in this example, is the brown line extending out and intersecting the curve at two points.
4. Find the points where it intersects the curve, and extend them down to determine the frequency values F_l, and F_u.
5. Calculate the bandwidth, by subtracting the lower frequency value (F_L) from the upper value (F_u), which is F_u-F_L.

Quality Factor Q

It is possible to express quality factor as resonance frequency (f) divided by bandwidth (delta f). If you had these two parameters, then you could easily calculate Q.

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