Walkie-talkie's working principle
2018/06/20 | by:

1, the launch part:

Phase-locked loops and voltage-controlled oscillators (VCOs) generate radio-frequency carrier signals that are transmitted through a buffer amplifier to stimulate amplification and power amplifiers to produce rated RF power. After passing through the antenna's low-pass filter, harmonic components are suppressed and then transmitted through the antenna. .

2, the receiving part:

The receiving part is a double-conversion superheterodyne method. The signal input from the antenna is subjected to radio frequency amplification after transceiving the conversion circuit and the band-pass filter. After passing through the band-pass filter, it enters a mixer and the amplified signal from the radio frequency comes from The first local oscillator signal of the phase locked loop frequency synthesizer circuit is mixed at the first mixer and generates a first intermediate frequency signal. The first intermediate frequency signal further eliminates the clutter signal of the adjacent channel through the crystal filter. The filtered first intermediate frequency signal enters the intermediate frequency processing chip and is mixed with the second local oscillator signal again to generate a second intermediate frequency signal, and the second intermediate frequency signal is amplified and discriminated by filtering through a ceramic filter to filter out unwanted spurious signals. Generate audio signals. The audio signal is amplified, band-passed, de-emphasized, etc. into the volume control circuit and amplification of the power amplifier to drive the speaker and get the information people need.

3, modulation signal and modulation circuit:

The human voice is converted into an audio signal by a microphone. The audio signal is directly modulated by an amplifier circuit, a pre-emphasis circuit, and a band-pass filter into a voltage-controlled oscillator.

4, signaling processing:

The CPU generates the CTCSS/CDCSS signal after being amplified and adjusted into the voltage controlled oscillator for modulation. After receiving the frequency-received frequency signal, a part of the low-frequency signal obtained through frequency discrimination is filtered and shaped by a band-pass filter that is amplified and sub-sounded, and then enters the CPU, and is compared with a preset value, and the result is controlled by the output of the audio amplifier and the speaker. That is, if the preset value is the same, the speaker is turned on, and if it is different, the speaker is turned off.