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1. Public network walkie-talkie


Also called card intercom, IP intercom, network intercom, 5000 km intercom, cluster intercom. It can be called 2G walkie-talkie, 3G walkie-talkie, and 4G walkie-talkie according to the corresponding operator signal.

Public network walkie-talkies refer to walkie-talkies that use the networks of operators (China Mobile, China Unicom, and China Telecom) to make calls. Similar to the principle of WeChat communication, the transmission distance of traditional walkie-talkies is generally from several hundred meters to several kilometers, and the communication distance is limited. Public network intercoms can realize national and global intercoms wherever operators have 4G/5G signals, wifi, and hotspots.

1. High cost performance

To realize long-distance communication for public network walkie-talkies, it does not need to set up related repeaters and lines, and can save a lot of manpower and material resources.

2 Shorter construction period and better timeliness

If the public network walkie-talkie is used to realize long-distance communication, it does not need to set up cables, and directly adopts the operator’s network, which can save a long period of construction and realize long-distance communication faster

3 Good adaptability

Due to the influence of external factors such as topography, weather, etc., some places are not suitable for erecting cables and repeaters, so traditional walkie-talkies may not be suitable at this time, and public network walkie-talkies do not have this concern

4 Good scalability

In our lives, we often need to add new equipment terminals on the basis of an existing communication network, and may need to destroy some of the original communication lines, but for public network walkie-talkies, we only need to regroup in the background It is easy to implement.

To achieve public network intercom, you must have the following factors at the same time.

1. Terminal-generally a handheld POC network walkie-talkie

The function of the terminal is to transmit and receive voice information, and some POC intercoms also have the function of a mobile phone

2. Platform

The wireless data network-based intercom voice service system realized by using VoIP technology is different from traditional walkie-talkies. There is no limitation on distance. As long as there is a wireless network, the service can be used, which is an extension and supplement to traditional trunking communication products; In addition, the system can also combine GPS, multimedia applications or other OA services to provide users with a multi-functional integrated dispatch system. The system easily realizes national real-time intercom, personnel positioning, patrol and attendance, video law enforcement and other scheduling functions. The system is powerful, easy to use, simple to install, and low in cost.

3. Flow Card

The main function of the flow card is the channel for the transmission of voice information.

Generally, there are WCDMA cards of China Telecom and GSM cards of China Unicom. Walkie-talkies applicable to WCDMA cards can not only realize intercom nationwide, but also realize global interconnection.

These three factors are indispensable for realizing public network intercom. If the national intercom is compared to railway transportation, the intercom is like a train, and the things on the train are our voice messages; the platform is a train dispatching system, which controls the whereabouts of the train, the distribution path, and the distribution time; the flow card is just It is like each station in the middle, responsible for tolls and tolls.


2. DMR digital walkie-talkie


DMR Digital Mobile Radio is a digital trunking communication standard that is an open standard designed and formulated by ETSI (European Communication Standards Institute) to meet the needs of mobile communication for low-end professional and commercial users in European countries. The digital mobile wireless system standard launched in April 2005. The latest version was announced in December 2007.


The DMR standard was drafted for low-end professional and commercial needs, and is applicable to industries such as public utilities, schools, hospitals, hotels, and property.


The DMR standard adopts TDMA (dual time slot) multiple access mode, 12.5KHz channel spacing, 4FSK modulation mode, and data transmission rate of 9.6Kb/s. This standard is divided into three stages. The first stage is a digital standard for free frequency bands, the second stage is a digital standard, and the third stage is a cluster stage.


DMR has the advantages of efficient use of spectrum resources, large-area networking mode, and compatibility with analog routines. Its business functions are rich, scalable, and backward compatible. At the same time, the system and terminal costs are lower, the network construction speed is faster, and the overall operation and maintenance cost is lower.


DMR walkie-talkies have the advantages of efficient use of spectrum resources and compatibility with analog routines. The DMR walkie-talkie has rich business functions, is scalable, and is backward compatible, while the maintenance cost is lower than other digital standards.


Three, analog walkie-talkie


The radio walkie-talkie has a wide coverage. Here we will collectively refer to radio communication equipment working in the ultra-short wave frequency band (VHF30~300MHZ, UHF300~3000MHZ) as radio walkie-talkies. In fact, according to the relevant national standards, it should be called an ultrashort wave FM radio telephone. People usually call a hand-held radio telephone with a small power and a small size as a "walkie-talkie". Someone used to call it a "walkie talkie" or "step". "Phone", and the high-power, large-scale wireless phone that can be installed in vehicles (ships) and other transportation or fixed use is also called "radio", such as vehicle-mounted station (vehicle-mounted station), marine station, fixed station, base station Station, transfer station, etc.


In terms of design technology, radio walkie-talkies can be divided into analog walkie-talkies designed with analog communication technology (also known as traditional walkie-talkies. Analog walkie-talkies modulate the stored signal to the transmission frequency of the walkie-talkie, and then send and transmit. The analog walkie-talkie mainly consists of 3 parts composition.


Launch part:


The phase-locked loop and voltage-controlled oscillator (VCO) generate the transmitted radio frequency carrier signal, which is buffered and amplified, stimulated and amplified, and power amplifier is used to generate rated radio frequency power. After passing through the antenna low-pass filter, the harmonic components are suppressed, and then transmitted through the antenna


Receiving part:


The receiving part is a double-conversion super-heterodyne method. The signal input from the antenna is amplified by the radio frequency after the transceiver conversion circuit and the band pass filter. After passing through the band pass filter, it enters a mixing frequency, and the amplified signal from the radio frequency is The first local oscillator signal of the phase-locked loop frequency synthesizer circuit is in the first mixer


Mix and generate the first intermediate frequency signal. The first intermediate frequency signal passes through the crystal filter to further eliminate the clutter signal of the adjacent channel. The filtered first intermediate frequency signal enters the intermediate frequency processing chip, and is mixed again with the second local oscillator signal to generate a second intermediate frequency signal. The second intermediate frequency signal is amplified and discriminated after filtering out unnecessary spurious signals through a ceramic filter. Generate audio signals. The audio signal passes through circuits such as amplification, band-pass filter, and de-emphasis, enters the volume control circuit and power amplifier for amplification, drives the speaker, and obtains the information people need. The signal processing human voice is converted into an audio electrical signal through a microphone, and the audio signal enters the voltage-controlled oscillator through an amplifier circuit, a pre-emphasis circuit and a band-pass filter for direct modulation. The CTCSS/DTCSS signal generated by the CPU is amplified and adjusted, and then enters the voltage-controlled oscillator for modulation. After receiving the low frequency signal obtained after frequency discrimination, part of it is amplified and sub-audio band-pass filter for filtering and shaping, enters the CPU, and compares with the preset value, and the result is used to control the output of the audio power amplifier and speaker. That is, if it is the same as the preset value, turn on the speaker, if it is different, turn off the speaker.


power control:


When the CPU controls in different states, it sends out different power sources. The receiving power supply is normally in intermittent working mode to ensure power saving; the transmitting power supply is only available during transmission; CPU power supply: stable power supply.


4. Broadband and Narrowband Converged Communication Terminal


As the name suggests, it combines the three-in-one DMR digital walkie-talkie, analog walkie-talkie, and mobile phone into one handheld terminal, also known as DMR digital-analog integrated walkie-talkie phone.


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