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How the walkie-talkie works
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How the walkie-talkie works

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Industry News
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Source:
2016/11/25 10:37
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[Abstract]:
The phase-locked loop and the voltage-controlled oscillator (VCO) generate the transmitted RF carrier signal, which is buffer amplified, stimulates the amplification, and the power amplifier generates the rated RF power.

How the walkie-talkie works

 1. Launch part:

The phase-locked loop and the voltage-controlled oscillator (VCO) generate the transmitted RF carrier signal, which is buffer amplified, stimulates the amplification, and the power amplifier generates the rated RF power. The antenna low-pass filter suppresses the harmonic components and then transmits them through the antenna. 

2. Receiving part:

The receiving part is a double-conversion super-heterodyne mode, and the signal input from the antenna is subjected to radio frequency amplification after being subjected to a transceiving conversion circuit and a band-pass filter, and after passing through a band-pass filter, entering a mixing frequency, the amplified signal from the radio frequency is derived 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 cancels the adjacent channel clutter signal through the crystal filter. The filtered first intermediate frequency signal enters the intermediate frequency processing chip, and the second local oscillation signal is mixed again to generate a second intermediate frequency signal, and the second intermediate frequency signal is filtered and removed by a ceramic filter to filter out unwanted spurious signals. Generate an audio signal. The audio signal is amplified by amplifying, bandpass filter, de-emphasis, etc., into the volume control circuit and the power amplifier to amplify, drive the speaker, and get the information people need.

3. Modulation signal and modulation circuit:

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

4. Signaling processing:

The CPU generates a CTCSS/DTCSS signal that is amplified and adjusted to enter the voltage controlled oscillator for modulation. The low frequency signal obtained after receiving the frequency discrimination is filtered and shaped by the bandpass filter of the amplification and sub-audio, enters the CPU, compares with the preset value, and controls the output of the audio power amplifier and the speaker. That is, if it is the same as the preset value, the speaker is turned on, and if it is different, the speaker is turned off.

There is no radiation problem when using intercom opportunities

The design of the walkie-talkie is in compliance with the relevant regulations of the Ministry of Information Industry [2001] No. 869, and will not cause harm to the human body. When using the walkie-talkie, it is not close to the human body, but 5 to 7 cm from the human body.

There are several factors that affect the distance and effect of the walkie-talkie.

1, system parameters:

1) The stronger the output power of the transmitter, the larger the coverage of the transmitted signal and the farther the communication distance. However, the transmission power should not be too large, and the transmission power is too large, which not only consumes electricity, but also affects the life of the power amplifier components, and is highly interfering, affecting the call effect of others, and also causing radiation pollution. The radio regulatory agencies of various countries have clearly defined the transmission power of communication equipment.

2) The higher the receiving sensitivity of the communication machine, the farther the communication distance is.

3) The gain of the antenna. When the antenna is matched with the machine, the antenna height is generally increased, and the receiving or transmitting capability is enhanced. The antenna used for the walkie-talkie is generally a spiral antenna, and its bandwidth and gain are smaller than other types of antennas, and are more susceptible to human influence.

2. Environmental factors:

Environmental factors mainly include paths, tree density, environmental electromagnetic interference, buildings, weather conditions, and terrain differences. These and other parameters directly affect the field strength and coverage of the signal.

3. Other influencing factors:

1) The battery is low. When the battery is low, the call quality will deteriorate. In severe cases, there will be noise, affecting normal calls.

2) Antenna matching, the frequency band of the antenna is inconsistent with the machine frequency band, and the antenna impedance is not matched, which will seriously affect the call distance. For the user, pay attention to tightening the antenna when changing the antenna. In addition, you can not use the antenna provided by the manufacturer, or use the antenna that does not meet the frequency of the machine.

3) The quality of sound depends mainly on the pre-emphasis and de-emphasis circuits. At present, there are more advanced speech processing circuits "applications of speech companding circuits and low-level expansion circuits", which have a good effect on fidelity speech.

4) Factors affecting the distance and effect of the intercom are also related to the season, and summer is better than winter.

1, the shell:

Professional machine generally uses PC+ABS, which has very good performance. It has good appearance, good aging and wear, and the product is sturdy and durable. Commercial machines often use engineering plastic ABS, which can be used in appearance, strength, wear resistance and aging. Very good to meet the requirements; button with silicone, wear-resistant, not easy to age, feel good; aluminum shell with lightweight material aluminum alloy ADC12, easy to form and follow-up treatment.

2, the host:

Generally include face shell, PTT button, earphone and power jack plug, PCB assembly, LCD part, volume / switch button, coding knob, indicator light, MIC, etc. The PTT button acts as a launch switch, typically on the side. The indicator light indicates the working status, usually at the top. There is also a volume/switch button and a coding knob (select channel) on the top of the radio. The LCD part visually displays the working status of the intercom. The PCB component is the core part of the walkie-talkie. The important components are on the PCB. Non-professionals are not allowed to disassemble. Most walkie-talkies have special shields, aluminum shells (fixed PCBs), etc. due to technical performance and drop resistance requirements. Professional machines also have waterproof requirements and the structure is more complicated.

3, battery:

The battery is divided into Ni-Cd, Ni-MH battery and Li-ion battery, and the capacity is 600mAh, 800 mAh, 1100 mAh, 1500 mAh. Lithium batteries are expensive and still in the development stage. Ni-Cd and Ni-MH batteries are more commonly used, and Ni-MH batteries are generally recommended for large-capacity batteries. The battery surface and the bottom case are ultrasonically welded, which is firm and reliable.

4, belt clip:

The function is to fix the walkie-talkie on the belt, and the belt clip can be removed for the convenience of the customer.

5. Antenna:

Divided into two parts: the antenna jacket and the antenna core. The antenna jacket is made of high-performance TPU material, which is resistant to bending and aging. The antenna core is generally connected to the main body by a threaded structure, which is easy to disassemble.

6, seat charge:

Use the AC adapter to charge the battery or the whole machine. The structure generally has a DC socket, a charging shrapnel, an indicator light, a button, and the like. The DC socket is connected to the AC adapter, and the shrapnel is connected to the battery pole piece. The indicator light indicates the charging state, and the button acts as a discharge. The charger can generally charge the battery and the whole machine.

7, in addition, the walkie-talkie also has holsters, headphones and other ancillary products.

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