Editing Tesla coil (section)

===Oscillation frequency===
To produce the largest output voltage, the primary and secondary tuned circuits are adjusted to [[resonance]] with each other.<ref name="Sprott"/><ref name="Anderson"/><ref name="Gerekos"/> The [[resonant frequency|resonant frequencies]] of the primary and secondary circuits, <math>\scriptstyle f_1</math> and <math>\scriptstyle f_2</math>, are determined by the [[inductance]] and [[capacitance]] in each circuit:<ref name="Sprott"/><ref name="Anderson"/><ref name="Gerekos"/>
:<math>f_1 = {1 \over {2\pi \sqrt {L_1 C_1}}} \qquad \qquad f_2 = {1 \over {2\pi \sqrt {L_2 C_2}}}\,</math>

Generally the secondary is not adjustable, so the primary circuit is tuned, usually by a moveable tap on the primary coil L<sub>1</sub>, until it resonates at the same frequency as the secondary:
:<math>f = {1 \over {2\pi \sqrt {L_1 C_1}}} = {1 \over {2\pi \sqrt {L_2 C_2}}}\,</math>

Thus the condition for resonance between primary and secondary is:
:<math>L_1 C_1 = L_2 C_2\,</math>

The resonant frequency of Tesla coils is in the low [[radio frequency]] (RF) range, usually between 50&nbsp;kHz and 1&nbsp;MHz. However, because of the impulsive nature of the spark they produce broadband [[radio noise]], and without shielding can be a significant source of [[radio frequency interference|RFI]], interfering with nearby radio and television reception.