1. the transmitting part: the phase-locked loop and the voltage-controlled oscillator (VCO) generate the transmitted RF carrier signal, which is buffered and amplified, stimulated and amplified to generate rated RF power, which is filtered by the antenna low-pass filter to suppress harmonic components, and then transmitted through the antenna. 2. Receiving part: The receiving part adopts the second frequency conversion superheterodyne mode. The signal input from the antenna is amplified by radio frequency after passing through the transceiving conversion circuit and the band-pass filter. After passing through the band-pass filter, it enters a mixer, and the amplified signal from radio frequency is mixed with the first local oscillator signal from the PLL frequency synthesizer circuit at the first mixer to generate the 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 the second intermediate frequency signal. The second intermediate frequency signal is filtered by a ceramic filter, amplified and frequency discriminated to generate an audio signal. Audio signals pass through amplification, band-pass filter, de-emphasis and other circuits, enter the volume control circuit and power amplifier for amplification, drive speakers, and get the information people need. 3. Modulation signal and modulation circuit: The human voice is converted into an audio electrical signal through a microphone, and the audio signal enters a voltage-controlled oscillator through an amplification circuit, a pre-emphasis circuit and a bandpass filter for direct modulation. 4. Signaling processing: The CTCSS/DTCSS signal generated by CPU is amplified and adjusted, and then enters the voltage controlled oscillator for modulation. A part of the low-frequency signal obtained after receiving frequency discrimination is amplified and filtered and shaped by the sub-audio band-pass filter, and then enters the CPU, where it is compared with the preset value, and its result controls the output of audio power amplifier and loudspeaker. That is, if it is the same as the preset value, turn on the speaker; if it is different, turn off the speaker. What are the main components of the intercom host? 1. Shell: Professional machines generally use plastic material PC+ABS with very good performance, which has good gloss, is not easy to age and wear, and the products are durable; Commercial aircraft often choose engineering plastic ABS, which can meet the requirements in appearance, strength, wear resistance and aging. The buttons are made of silica gel, which is wear-resistant, not easy to age and feels good; The aluminum shell is made of light aluminum alloy ADC12, which is easy to form and follow-up treatment. 2. Host: generally including face shell, PTT button, earphone and power plug, PCB assembly, LCD part, volume/switch button, coding knob, indicator light, MIC, etc. PTT button plays the role of transmitting switch, usually on the side. The indicator light indicates the working state, usually at the top. There are also volume/switch buttons and coding knobs (channel selection) on the top of the intercom. The LCD part visually displays the working state of the walkie-talkie. PCB assembly is the core part of walkie-talkie. Important devices are all on PCB, and non-professionals are not allowed to disassemble it. Most walkie-talkies have special shielding cover and aluminum shell (fixed PCB) due to technical performance and anti-drop characteristics. Professional machines also have waterproof requirements, and the structure is more complicated. 3. Batteries: The batteries are divided into Ni-Cd, Ni-MH and Li-ion batteries, with capacities ranging from 6mAh, 8 mAh, 11 mAh and 15 mAh. Lithium batteries are expensive and still in the development stage. Ni-Cd and Ni-MH batteries are widely used, and Ni-MH batteries are recommended for general large-capacity batteries. The battery surface and bottom case are welded by ultrasonic wave, which is firm. 4. Belt clamp: The function is to fix the walkie-talkie on the belt. For the convenience of customers, the belt clamp is detachable. 5. Antenna: It is divided into two parts: antenna jacket and antenna core. The antenna jacket is made of high-performance TPU material, which has good bending resistance and aging resistance; Generally, the antenna core is connected to the main engine with a threaded structure, which is convenient to disassemble. 6. Seat charging: it is used to charge the battery or the whole machine with the fire cow. Generally, there are DC sockets, charging shrapnel, indicator lights, buttons and so on. The DC socket is connected with the fire bull, the elastic sheet is connected with the battery pole piece, the indicator lamp indicates the charging state, and the key plays a role in discharging. Seat charger can generally charge the battery and the whole machine. 7. In addition, the walkie-talkie also has accessories such as holsters and headphones for customers to choose from. Please refer to the circuit diagram for details.

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