Bandwidth, BW

The bandwidth defined by $f_p$ is $$\bbox[10px,border:1px solid grey]{BW= f_2 -f_1 = {f_p \over Q_p}}$$ By substituting $Q_p$ from the previous topic, we can show that $$BW= f_2 -f_1 \appro {f_p \over Q_l} = {f_p \over X_L/R_l}\\ = {f_p R_l \over 2 \pi f_p L} = {R_l \over 2 \pi L} $$ Hence, $$\bbox[10px,border:1px solid grey]{BW= f_2 -f_1 \appro {R_l \over 2 \pi L}}$$