41. IF is called the " image frequency " and must be rejected by the tuned circuits in the RF stage. 42. By adjusting the tuning of this tuned circuit , Armstrong was able to dramatically increase the gain of the Audion amplifier. 43. Radio frequency VCOs are usually made by adding a varactor diode to the tuned circuit or resonator in an oscillator circuit. 44. The tuned circuit , consisting of a coil and a capacitor connected together, acts as a resonator, similar to a tuning fork. 45. This audio signal can be heard separate from the video, using standard analog FM radios equipped with the appropriate tuning circuits . 46. When using a tuned circuit in the input, the network must match the driving source to the input impedance of the grid. 47. The signal bandwidth of the amplifier is limited by the Q-factor of the tuned circuit but this is not a serious limitation. 48. A tuned circuit could block AC of one narrow band of frequencies, or allow passage of AC of one narrow band of frequencies. 49. An RF amplifier may have tuned circuits at both its input and its output, so three or more tuned circuits may be tracked. 50. An RF amplifier may have tuned circuits at both its input and its output, so three or more tuned circuits may be tracked.
