The influence of high frequency on the circuit is mainly reflected in capacitors and triode elements.

1. For capacitive elements: the capacitance is not conductive to DC, and the capacitive reactance x= 1/2πfc, so the capacitive reactance is very small for high-frequency AC signals, and the capacitance is conductive to high-frequency signals.

2. For triode components: triode has no amplification effect on DC signal. It will greatly amplify high-frequency AC signals, thus forming such various electronic components.

High frequency is the signal frequency of 3-30 MHz, which is only a narrow understanding of high frequency. And high frequency, including the frequency range from 3MHz to X00GHz, can be called high frequency. After receiving the high-frequency signal of a certain channel, the TV set must demodulate the complete TV signal from the high-frequency signal in order to reproduce the video image on the screen.