Unlike mobile phones, walkie-talkies don't have to be charged according to the call time. Comparing the cost of mobile phones and two-way walkie-talkies, users will find that walkie-talkies are more economical and practical.

Working principle of visual interphone:

1, transmission part:

A phase-locked loop (PLL) and a voltage-controlled oscillator (VCO) generate a transmitting RF carrier signal, which is buffered, amplified and amplified to generate rated RF power, and harmonic components are suppressed by an antenna low-pass filter, and then transmitted by an 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 transceiver conversion circuit and bandpass filter, and then enters the mixer. An amplified signal from a radio frequency is mixed with a first local oscillator signal from a PLL frequency synthesizer circuit at a first mixer to generate a first intermediate frequency signal. The first intermediate frequency signal further eliminates the clutter signals of adjacent channels through a 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 IF signal is filtered, amplified and frequency-discriminated by a ceramic filter to generate an audio signal. After amplification, band-pass filtering, de-emphasis and other circuits, the audio signal enters the volume control circuit and power amplifier for amplification, driving the speaker and getting the information people need.

3, modulation signal and modulation circuit:

The human voice is converted into an audio signal through a microphone, and the audio signal enters a voltage-controlled oscillator through an amplifier circuit, a pre-emphasis circuit and a band-pass 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 low-frequency signals obtained after receiving frequency discrimination are amplified, filtered and shaped by a sub-audio band-pass filter, and then enter the CPU, where they are compared with preset values, and the results control the output of the audio power amplifier and speakers. That is, if it is the same as the preset value, turn on the speaker; If not, please turn off the speakers.

The host of the video interphone includes the following components:

1, shell:

Professional machines generally use plastic material PC+ABS with very good performance, which has good luster, 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 silicone, which is wear-resistant, not easy to age and feels good; The aluminum shell is made of light aluminum alloy ADC 12, which is easy to be molded and subsequently processed.

2. Moderator:

Generally, it includes 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 status, 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 of walkie-talkie. Important devices are all on the PCB, and non-professionals are not allowed to disassemble them. Most walkie-talkies have special shielding cover and aluminum shell (fixed PCB) because of their technical performance and anti-falling characteristics. Professional machines also have waterproof requirements, and the structure is more complicated.

3. Battery:

Batteries can be divided into Ni-Cd, Ni-MH and Li-ion batteries with capacities ranging from 600mAh, 800mAh, 1 100mAh and 1500mAh. Lithium batteries are expensive and are still in the research and development stage. Nickel-cadmium and nickel-hydrogen batteries are widely used, and nickel-hydrogen batteries are generally recommended for large-capacity batteries. The battery surface and bottom case are welded by ultrasonic wave, which is firm and reliable.

4. Belt clamp:

The function is to fix the interphone on the belt, and the belt clip is detachable, which is convenient for customers to use.

5. Antenna:

It is divided into two parts: antenna sheath and antenna core. The antenna sheath is made of high-performance TPU material, which has good bending resistance and aging resistance; Generally, the antenna core is connected with the main machine with a threaded structure, which is convenient to disassemble.

6. Seat filling:

Used with fire cow to charge the battery or the whole machine. 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. The 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.