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Let's learn about the walkie-talkie.

2025-01-19 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > IT Information >

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Shulou(Shulou.com)11/24 Report--

After 3202 years, mobile phones are so easy to use, why are people still using walkie-talkies?

That is because walkie-talkies do not rely on the network, do not generate phone fees, and are connected as soon as a dozen, so there is always a place for walkie-talkies in the world of communication equipment.

Today, learn about the "walkie-talkie" with the document gentleman.

What is walkie-talkie? Communication signals are invisible radio waves that are constantly sent and received in the air. The old radio is a device that can only receive radio waves. Walkie-talkie (two way radio) is a device that can both receive and transmit radio waves. Walkie-talkies with high power, large volume and fixed installation in a certain place (car, ship) are called radio stations. The walkie-talkie, which is small in power, small in size and can move around in your hand, is called a handheld walkie-talkie, and it is also the most common walkie-talkie we see.

From the outside, the walkie-talkie seems to be an old-fashioned "mobile phone". It is bulky without a beautiful screen. People can't help but wonder what such "antiques" can be used for in the 21st century. Despite its simple appearance and simple function, walkie-talkies work in much the same way as mobile phones.

The call process between a walkie-talkie and a mobile phone is similar: receiving input (which can be voice or text)-- > processing information (encoding the input into a signal)-> sending a signal (sent to another walkie-talkie or sent to an application server through the operator's network).

The process of speaking on a walkie-talkie (take common circuits as an example) is as follows:

Similar to the voice operation of Wechat, we have to keep pressing and holding down the PTT button (PUSH TO TALK) before we can speak. After the sound is picked up by the microphone, it is converted into an audio electrical signal.

The processor inside the walkie-talkie processes the electrical signal to generate the transmitted RF carrier signal, and uses buffer amplification, excitation amplification, power amplifier and other ways to form the rated RF power.

The transceiver bandpass filter suppresses the harmonic components in the electrical signal and transmits the signal through the antenna.

The process of answering incoming calls on walkie-talkies and mobile phones is similar: receiving a signal (from another walkie-talkie or application server)-- > processing information (decoding the signal into voice or multimedia)-> output display.

The process of answering a walkie-talkie (take common circuits as an example) is as follows:

After the walkie-talkie is turned on, it has been in the state of receiving signals.

Once the information is received from the antenna, the signal is processed:

The amplified signal from the radio frequency and the first local oscillator signal from the phase-locked loop frequency synthesizer circuit are mixed at the first mixer and a first intermediate frequency signal is generated.

The first intermediate frequency signal further eliminates the clutter signal of the adjacent channel through the crystal filter, and then enters the intermediate frequency processing chip, which is re-mixed with the second local oscillator signal from the phase-locked loop frequency synthesizer circuit to generate a second intermediate frequency signal.

After filtering the useless spurious signal through a ceramic filter, the second intermediate frequency signal is amplified and discriminated to generate an audio signal.

The audio signal is processed by amplifying, band-pass filter, de-emphasis and other circuits, and converted into audio.

The volume control circuit and power amplifier amplify the audio and drive the loudspeaker to play the audio.

Compared with mobile phones, the characteristics of walkie-talkies are very obvious:

Do not rely on the communication process of network mobile phones, need the support of various networks, including: wireless access network, bearer network, core network and external network. Only such a large and complex network can support smooth calls and a good Internet experience for hundreds of millions of mobile phones. Students who are interested in network support can read that it is not so easy to fall in love. Everyone has his mobile phone.

Communication between walkie-talkies does not require so much network. For two walkie-talkies that have established a call channel, you can talk to each other at will as long as you press the call button. If multiple walkie-talkies are on the same channel, one walkie-talkie starts to talk, and all the other walkie-talkies can receive sound.

Not generating a walkie-talkie is equivalent to an upgraded version of "talking basically depends on roaring", which converts people's sounds into invisible airwaves, which are free of charge. If frequent calls are needed, walkie-talkies can save a lot of money on calls. After all, there is no need to go through the communication network, which saves the "price difference" of many middlemen. Ps: the airwaves are free, but you still have to pay for the channels you occupy.

In the process of making a phone call, the signal needs to be processed by the communication network: find the other party's mobile phone and ring, and wait for the other party to answer before the two sides can make a formal call. Although the process is fast, walkie-talkies can be faster: as soon as the button is pressed, the two sides can talk, minimizing the waiting time before answering. In specific scenarios that require rapid response, walkie-talkies can greatly improve the efficiency of communication, so that some things that require teamwork can be well accomplished in a unified command and coordinated way.

The "seven weapons" of walkie-talkies, which are not handsome but have outstanding features, actually rely on these "seven weapons":

The working frequency band of the walkie-talkie is assigned and managed by the China Radio Administration Commission. According to the regulations, professional walkie-talkie VHF section 136 MHz~174 MHz and UHF section 400 MHz~470 MHz, outdoor hiking 433 MHz, mobile phone 900MHz / 180MHz, civil 409 MHz~410 MHz. Although there are many working frequency bands, the frequency band we use in our daily life is 409 MHz~410 MHz, so we must not exceed the regulations to use other frequency bands, so as not to interfere with other people in the dedicated frequency band.

According to the fixed step size (for example, 25 KHz (broadband), 20 KHz, 12.5 KHz (narrowband)), the working frequency band can be divided into multiple communication channels, such as 409.7500 MHz, 409.7625 MHz, 409.7750MHz, 409.7875 MHz, 409.8000 MHz. The most commonly used walkie-talkies are 20 channels between 409.7500 MHz~409.9875 MHz.

With so many communication channels, do we still need to try one by one? Of course not, the walkie-talkie provides channel scanning function: there is a dedicated button, after pressing, the walkie-talkie will try to receive signals one by one according to a certain order of communication channels. If you try 100 ms per channel, you can try to scan 10 communication channels in a second, then the scanning speed is 10 ch / s.

Transmission power is an important index of walkie-talkie, the greater the power, the greater the distance between the two walkie-talkies. The power of civil walkie-talkies is less than 0.5 watts, and walkie-talkies with more than 0.5 watts need to apply for a radio license to use. The power of hand-held walkie-talkies is generally less than 5 watts, while the power of vehicle-borne ship radios is relatively large, ranging from 25 watts to 50 watts, or even 100 watts.

Under the condition that the call range depends entirely on the walkie-talkie to send and receive radio waves, the distance between the two walkie-talkies is affected by power, obstacles and other factors. In an open environment, a handheld walkie-talkie can maintain clear call quality within 03km. In the environment of many high-rise buildings in the city, the best range of handheld walkie-talkies is within 1-2 kilometers.

Antenna We know that the higher the frequency of the radio wave, the shorter the wavelength, and the shorter the antenna that receives the radio wave. Because the walkie-talkie uses a lower working frequency band, if you want to receive radio waves, the length of the antenna is relatively long. So when you see a "long-eared" handheld device, it's likely to be a walkie-talkie.

In order to have a longer battery life, the walkie-talkie is not only equipped with large-capacity batteries, but also provides automatic power-saving function. If a walkie-talkie does not send a signal for a long time, it will automatically "sleep" for a period of time and will not "wake up" until it receives a new signal or press the key to operate.

The structure of the walkie-talkie is simple, and in order to use in the complex outdoor environment, but also designed waterproof, dustproof, anti-seismic and other functions, strong and durable.

The application scene of the walkie-talkie looks very good, but there is still a big gap between the walkie-talkie and the mobile phone in function and appearance. With a cell phone, is it necessary to use a walkie-talkie?

Mr. documentation feels that it is necessary because the walkie-talkie has its own unique application scenarios, including:

Emergency communication is at risk of network interruption in some extreme weather conditions. when the mobile phone cannot make a call due to network interruption, the independent network characteristics of the walkie-talkie ensure that it can still communicate with other walkie-talkies in this case. Establish contact with the outside world. Walkie-talkie is a very practical and powerful emergency communication equipment. For more information on emergency communications, you can see how to ensure emergency communications after a major earthquake or disaster.

Field, basement, tunnel although the communicator has covered a large area of the earth, but in the field, basement, tunnel and other environment, the base station may not be covered, and the walkie-talkie can play a role.

Medical places, business supermarkets, large-scale event sites in these need to race against the clock, efficiency first environment, walkie-talkie simple, direct, so that communication becomes more rapid and effective.

The development of walkie-talkies walkie-talkies have undergone many changes since their invention. the current types of walkie-talkies include:

The traditional walkie-talkie is the earliest and most widely used walkie-talkie, which uses the analog signal to modulate the signal to the communication frequency band of the walkie-talkie. Two walkie-talkies need to use the same communication channel within the call range in order to make a successful call.

Digital walkie-talkie uses digital signal, which converts voice into digital coding and propagates between different walkie-talkies, which can effectively avoid noise, distortion and other problems in the process of communication. Time division multiple access (TDMA) is adopted, which allows multiple users to use the same frequency band at the same time, thus increasing the communication capacity and making one walkie-talkie talk with more walkie-talkies.

IP walkie-talkie (public network walkie-talkie) is to connect the walkie-talkie to our existing communication network to achieve the expansion of communication distance. For this type of walkie-talkie, after the Internet of things card is installed, the maximum distance can be more than 5000 kilometers. In addition to the original long antenna, the public network walkie-talkie has also added an antenna, which is specially responsible for establishing communication with the base station. However, because the communication frequency of the mobile phone is much higher than that of the walkie-talkie, the new antenna is relatively short and can be hidden inside the walkie-talkie. IP walkie-talkie uses the existing communication network to make calls, which is essentially no different from mobile phones.

How's the conclusion? Do you know more about a communication device today?!

Like his fans, Mr. documentation has learned something new:

The working principle of walkie-talkie and mobile phone is similar. The core of technology is the same, and the same seed can produce different flowers.

In certain situations, the advantages of walkie-talkies are obvious. Heaven does not give birth to useless people, find the right field, everyone can be glowing gold.

From analog to digital to IP (public network) development, walkie-talkies are also in constant evolution. Moving forward is a never-ending road, but fortunately there are a lot of people traveling with it.

This article comes from the official account of Wechat: ZTE documents (ID:ztedoc)

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