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 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 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 factors affecting the communication distance and effect of walkie-talkie are as follows:
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, which not only consumes power and affects the life of power amplifier components, but also has strong interference, which affects the communication effect of others and will also produce radiation pollution. Radio regulatory agencies in various countries have clear regulations on the transmission power of communication equipment.
2) The higher the receiving sensitivity of the communicator, the farther the communication distance.
3) the gain of the antenna. When the antenna is matched with the machine, the height of the antenna is usually increased and the receiving or transmitting ability is enhanced. The antenna used in hand-held walkie-talkies is generally a spiral antenna, which has smaller bandwidth and gain than other kinds of antennas and is more easily influenced by human body.
2. Environmental factors:
Environmental factors mainly include path, tree density, electromagnetic interference of environment, buildings, weather conditions and terrain differences. These factors and other parameters directly affect the signal field strength and coverage.
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, which will affect the normal call.
2) Antenna matching: the frequency band of the antenna is inconsistent with the machine frequency band, and the antenna impedance is mismatched, which will seriously affect the call distance. For users, pay attention to tighten the antenna when replacing it. In addition, you can't use antennas provided by non-manufacturers casually, and you can't use antennas that don't meet the machine frequency.
4. Sound quality mainly depends on pre-emphasis and de-emphasis circuits. At present, there is a relatively advanced speech processing circuit "the application of speech companding circuit and low-level expansion circuit", which has a good effect on fidelity speech.
* What is the main component of intercom host?
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, 800 mAh, 1 100 mAh and 1500 mAh. 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.
* What are the procedures for purchasing walkie-talkies?
The use of walkie-talkies to occupy frequency resources must be applied to the local radio management Committee and approved by the Committee before they can be purchased and used. The specific procedures are as follows:
1. Ask the CSRC or the designated dealer for the Application Form for Setting up a Radio Station;
2. When filling in the form, the use area, purchase quantity and purpose must be clearly filled in and stamped with the official seal of the unit;
3, with the declaration form to the District Secrecy Bureau (generally in the district government organs) for the record, the District Secrecy Bureau for examination and approval, sign an opinion on the application form, and return the form to the applicant;
4. Report to the Committee with the Application Form. No committee for examination and approval and approved the frequency of use, to the applicant issued a "quasi purchase card",
5. Buy walkie-talkies with a "quasi-purchase certificate";
6. Pay the frequency occupation fee (per set 100.00 yuan per year) to the inspection committee with the walkie-talkie and the quasi-purchase certificate receipt. No "Radio Station License" was issued.
The use of public walkie-talkies does not require a license, and the frequency occupation fee is free. Users (or units) only need to fill in the registration card provided by the manufacturer to purchase public walkie-talkies.
* Why is there a frequency limit when using walkie-talkies?
In order to ensure that most users' calls are not disturbed and make rational use of frequency resources, the National Radio Regulatory Commission has divided the use of frequencies and stipulated that different industries should use corresponding frequency ranges. When purchasing walkie-talkies, users should apply to the local radio management committee for frequency points.
* What is a public intercom?
Public walkie-talkie refers to the wireless walkie-talkie with emission power not more than 0.5W and working at the specified frequency. Its radio frequency, power and other radio frequency technical indicators must meet the following requirements:
1, working frequency (.9000; 409. MHz): 409.7500, 409.7625, 409.7750, 409.7875, 409.8000, 409.8 125, 409.8250, 409.8375, 409.8500. 4099 125、 409.9250、 409.9375、 409.9500、 409.9625、 409.9750、409.9875;
2. Modulation mode: F3E；;
3. Effective transmit power (EIRP):
4. Emission frequency tolerance:
5. Transmitter stray radiation: < 50uW
6. Stray radiation of the receiver:
7. Channel spacing:12.50khz.
* Is there a charge for talking on the intercom?
No matter how often you use regular walkie-talkies, there is no charge, and each walkie-talkie only needs to pay a frequency occupation fee of tens of yuan every year. If you use the public walkie-talkie, you don't need to pay any fees.
* Can mass consumers buy walkie-talkies?
The communication distance of conventional walkie-talkies is generally 3~5 kilometers, but it will be relatively short when there are tall buildings or mountains blocking it. With network support, intercom can reach tens of kilometers.
Why do people choose to use walkie-talkies today when mobile phones are very popular?
This is because compared with mobile phones, walkie-talkies have many unique functions:
1, intercom is not restricted by the network, and intercom allows users to communicate easily in places not covered by the network;
2. The walkie-talkie provides one-to-one and one-to-many calls, which is simple to operate and makes communication more free, especially in the case of emergency dispatch and collective cooperation.
3. The call fee is low.
* What fields are walkie-talkies mainly used for?
Walkie-talkies are mainly used in public security, civil aviation, transportation, water conservancy, railway, manufacturing, construction, service and other industries, and are used for communication and command and dispatch among group members, so as to improve communication efficiency and quick response ability in dealing with emergencies. With the introduction of walkie-talkies into the civilian market, people began to use walkie-talkies more and more when they went out to travel and shop.
* Daily maintenance of interphone
1. The walkie-talkie has been used for a long time, and it is easy to get dirty when the button, control knob and casing are pressed. Please remove the control knob from the walkie-talkie and clean the casing with neutral lotion (do not use strong corrosive chemicals) and wet cloth. The use of chemicals such as cleaning agents, alcohol, sprays or petroleum preparations may damage the surface and casing of the walkie-talkie.
2. Use the walkie-talkie carefully. Never move a walkie-talkie with a portable antenna.
3. When the accessories are not applicable, please cover the dust cover (if equipped).
* interphone use safety precautions
1, in a car with an airbag, don't put the walkie-talkie in the range that may be involved when the airbag is deployed. If the walkie-talkie is in the area that may be involved when the airbag is deployed, once the airbag is deployed rapidly, the walkie-talkie may hurt people in the car with great impact.
2. In a potentially explosive atmosphere or occasion, unless the walkie-talkie is specially certified, it must be turned off. In a potentially explosive environment, electric sparks can lead to explosion or fire.
3. Do not replace or charge the battery in an environment with potential explosion danger. When installing and removing batteries, contact sparks may occur and lead to explosion.
4, before near the blasting area and detonator area, must first turn off the intercom, so as not to cause possible explosion.
* Matters needing attention in interphone operation
1. When the walkie-talkie is transmitting, keep the walkie-talkie in a vertical position and keep the distance between the microphone and the mouth 2.5-5cm. When launching, the walkie-talkie should be at least 2.5 cm away from the head or body. If the hand-held walkie-talkie is carried with you, the antenna should be at least 2.5 cm away from the human body when transmitting.
2. Don't switch it on and off many times during use, and adjust the volume to the volume suitable for your hearing.
* battery use precautions
1. Use original or approved batteries.
2. If metal conductors such as jewelry, keys or beads come into contact with the exposed electrodes of batteries, all batteries may cause damage or personal injury. Please use the charged battery carefully, especially when you put it in your pocket, wallet or other metal container.
3, charging must be carried out in the environment of 5~40 degrees. If it exceeds this temperature range, it will affect the battery life, and it may not be enough to charge to the rated capacity.
* Precautions for antenna use
1. Only original or approved antennas can be used. Unauthorized antennas, antennas modified or added with accessories may damage walkie-talkies or violate the regulations of the Radio Administration Bureau of the Ministry of Information Industry.
2. Do not hold the antenna by hand when using it.
3. The walkie-talkie antenna can't be unscrewed, otherwise the power tube will be easily burned when launching.
4. Don't use the damaged antenna. When launching, if the damaged antenna touches the skin, it may cause minor burns.