Only two way radios which directly use digital signal processors can be called the real sense of digital two way radios, while those use the digital control signal (such as two way radios of the cluster system) can not be called digital two way radios.

Digital two way radios have many advantages. The biggest advantage is making better use of spectrum resources, which is similar to the cellular digital technology.
 
First, digital two way radios can load more users in a designated channel such as 25KHZ and improve the spectrum utilization, which is a solution to the crowded frequency, with long-term significance.
 
Second, digital two way radios can improve the quality of voice. Because digital communication technology has in-system error correction function, compared with analog-interphones, two way radios can be used in a wider range of signal environment and can achieve better voice and audio quality, with fewer received audio noises but clearer voice.
 
Third, digital two way radios can improve the voice and data integration and change the weaknesses that the control signal will be weakened as the communication distance is increased. Compared with similar integrated analog voice and data systems, digital two way radios can provide better data processing and interface functions so that more data applications can be integrated into the same two-way wireless communication base station structure for more perfect and convenient voice and data service integration. 

These three characteristics make digital two way radios become the future trend of the development of two way radios technology.

In the 1970s, Motorola introduced digital technology into the two way radios system design. In 1975, it produced a digital voice-encrypted DVP radio, and in 1980, it developed a digital data communication system. In the 1991 Desert Storm operation, 35,000 digital two way radios were used. Obviously, with the development of radio communication technology, people's improved demand for wireless communication quality and the increasing spectrum resources, digital two way radios will have a huge demand market. But no matter how extensive the applications of digital two way radios are, the very mature simulation technology in the radio technology will continue to serve for the design of the two way radios in a very long period of time, making two way radios have small sizes, low costs, powerful functions and become more commercial, to meet the different needs of communication users. Digital two way radios can not replace the analog-interphones in a short time. These two two way radios will play their own roles and develop together.
 
Until 2010, many manufacturers have launched their own definition of communication protocol digital two way radios, but the open standards for digital radio are dPMR and DMR these two protocols. The standards for the dPMR protocol is "ETSI TS 102 490", "ETSI TS 102 658". The standard for the DMR protocol is "ETSI TS 102 361-1, 2, 3, 4". These two communication protocols have relatively low starting points, far from the current (2010) wireless public network communication protocol. As the digital process of the two way radio industry is very slow, some people jokingly talk about the field that it is the last digital electronics industry.

Why do we use two way radios?
Why do people choose to use two way radios nowadays when mobile phones are so popular? The reason is that compared with mobile phones, two way radios have their own features.
1. Two way radios are not restricted by the network, thus they can provide easy communication for users in the places where the network is not covered.
2. Two way radios provide talking service in one-to-one and one-to-many ways. We can talk by the simple operation of one click, which makes communication freer. These features are very important especially in the case of emergency scheduling and collaboration.
3. Two way radios have very low communication costs.

How long is the communication distance of two way radios?
Radio communication does not have the "distance" indicator, because the ultra-short wave communication belongs to the line-of-sight propagation, and the signal can be blocked and disturbed by buildings, hills, woods, electromagnetic fields, etc., affecting the actual communication distance and quality. In the ideal state (without any obstruction and interference), the communication distance of professional two way radios can reach 10 kilometers or farther, while the actual communication distance generally is only 3 to 5 kilometers. If there is interference of tall buildings, high mountain blocking or space electromagnetic fields, the communication distance sometimes can be so short that the communication is failed.
 
Can common consumers buy two way radios?
Common consumers can also buy two way radios, but in the past, before purchasing and using two way radios, people had to apply for a radio license from the local radio management committee and paid the frequency occupancy fee. Since December 6, 2001, China's civilian two way radio market has been open. People do not have to fulfill any formalities if they use the 400MHz civilian two way radios whose transmission power is less than 0.5 watts.
 
Can we make phone calls with two way radios?
With the support of internet, two way radios can be used to make phone calls, which can not be realized if it is just a common call between two way radios without internet.
 
Need we pay for the communication with two way radios?
We do not have to pay any fees if we communicate with the common two way radios. No matter how frequently we use two way radios, we only need to pay a few dozen yuan for the frequency occupancy and we needn't pay any fees if we use the public two way radios.

All of us may have heard about 4G network, 5G network and WIFI. Now it is time to welcome MMW. MMW is the abbreviation of millimeter-wave. It refers to a kind of radio transmission technology realized by millimeter spectrum. This is the technology what Facebook now is trying to work with the technology. Last year, this company begin the initial test of this technology with the help of the UAV Aquila. However, it ended with a failure.

But now, Facebook seems to have enough sufficient preparations. Earlier this month, Facebook announced that their MMW radio technology set a new record in speed , which quadrupled the download speed. Previously, the best record of MMW is to support the play of 1000 high-definition movies at the same time, while this digital can be increased to 4000 movies now.

However, Facebook now still test the latest technology by the Aquila. Mike Schroepfer, the CTO of Facebook has pointed out that the final goal of Aquila is to bring the network to 4.1 billion people who still have not connected with internet yet.

We can always hear the sound of sirens of ambulance on the road. According to the report by foreign media, a student team from Swedish Royal Institute of Technology(KTH) has developed a system called EVAM. This kind of system allows the car stereo to remind other drivers that the ambulance is close. The ambulance needn’t sound the sirens. EVAM system will allow the ambulance sending FM radio signal to the car in front of it. The fast traffic moving is, the far conveyance will be.

As is known, the radio digit system on the car itself can receive these signals. This will lead to a stop of the audio presentation-no matter the radio, CD or other resources. At the same time the EVAM system can make a sound of voice notice that the ambulance is closing and the relative text message will show on the screen.

The researchers predict that the EVAM system should sound the sirens to at least two thirds of the cars on the road. They will proceed the first pilot project in the first season of this year in the Stockholm.
 

According to the report by Russian Message dated Dec 5, 2016, the Russian Ministry of the National Defense has ever tested on the radio station which conveys the message by microwave radiation. This technology is unique in the world. According to the report, the new type “Emerald” Piecemeal can not only convey the voice message and digital, but also can control drone, robot and air defense. But electronic detecting equipment till now have no ability to detect the banner signal of “the Emerald” and distinguish the signal from the natural music sound.

It is said by Zaitsev, a professor of Russian Air Defense Military College, said to Message: the Emerald Piecemeal prototype has ever stopped exhibiting to Shoigu, the Minister of National Defense. According to his request, the test is stopped when the General Consultant Representive is presented. The test result indicates the invisible ability of the equipment.“The emerald”has an applied area of one to 10 kilometers. Its wave length is from 200 to 1000 Hz. The digital convey speed is neal 3000 digits/second. These ability digits can guarantee to stop the several thousand times of conveyance among the equipments at the same time.

As reported, today’ s manufacturing has used the microwave radiation technology for contacting equipment which is the priority category for all the prosperous countries to grasp “the Piecemeal”.

Message cites Mr Kejulin’s saying, the professor of the Military Superstition College: “As long as Russia can create the entity, then we can stop testing successfully. If the common radio station banner signal can be detected within 15 kilometers, then the ‘Emerald’ can stop location 30 kilometers away from the Piecemeal. Recently we build up the invisible contact equipment on the base of the‘Emerald’, which is from the single soldier used mini station to the complex short-range communication”.

In the wireless intercom systems, there are a variety of antenna output signal need to be calculated according to construction structures, on that condition, the two way radio power splitter play its role.

Power splitter is a kind of devices that divide one way input signal energy into two or a plurality of equal or not equal energy, it can also combine the multipath signal energy into one to output, at this point, power splitter also known as a combiner. The output ports of power splitter should keep a certain degree of isolation. According to the output, Power splitter is usually divided into two parts (one input and two outputs), or it is divided into three parts (one input and three outputs), etc. Main technical parameters of the power splitter are power loss (including insertion loss, distribution loss and reflection loss), the voltage standing wave ratio in different ports(VSWR), isolation between power allocation ports and amplitude balance, phase equilibrium, power capacity, and the band width.

Effect: Power splitter is to proportionally allocate the signal of two way radio system.

Specifications: two power splitter, three power splitter, four power splitter.

The power splitter is a device which is divided one way radio frequency input signal into two equal parts, the output ports of the power splitter should ensure a certain of isolation.

The technical index of the power splitter include frequency range, bearing power, the allocation loss of the main path to the branch, the insertion loss between input and output, the isolation between the branch ports, the voltage standing wave ratio of each port and so on.

Function of power splitter:

A. Frequency range: This is the premise of all kinds of RF / microwave circuit, the design structure of power splitter is closely related to the working frequency.

B. Bearing power: the maximum power, high power signal splitter and circuit components can withstand, is the core indicators, which determines what kind of transmission line to achieve the design task.

C. Coupling loss: the distribution loss of the main road to the branch is essentially related to the specification of the power splitter.

D. Insertion loss: the insertion loss between the input and output is due to the medium or conductor of the transmission line is not ideal and other factors.

E. Isolation degree: the isolation degree between the branch ports is another important index of the coupling splitter.

F. Standing wave ratio:  The voltage standing wave ratio in each port is the smaller, the better.
 

There are use methods and attentions that need to be noticed when using a two way radio.

Use methods :

1. Press the button, users can speak. Loosen the button, and users can answer.

2. When there is no antenna installed, wireless communication equipment is banned from launching.

3. The hand-held radio cannot launch when charging, users should turn off the power switch and then charge.

4. When users did not receive call signals, they should not ask or bark easily or do horizontal contact.

5. When the transmitter is not clear, users can change their own location, moving around and looking for the best communication position; the vehicle radio station in driving can enhance the sensitivity and improve the communication effect by slowing down the vehicle speed or stopping driving.

6. The hand-held radio is prohibited from using when it is within one meter away from the power stations to prevent it burn out the speaker; using a handheld radio should stay away from the computer, so as to avoid interference.

7. The voltage range of radio, the handheld radio’s direct current is 7.2V, while the direct current of the fixed radio and the vehicle radio are 12V. In the use of external power supply, the voltage which is beyond voltage range must not be used, otherwise it will damage the radio.

8. The handheld radio charger cannot be used for charging for other battery. Radio users cannot equip radio with ordinary battery to prevent the electric water entry into the radio and rotten radio. Besides, users shall not change the function of the battery of radio.

9. Users should pay attention to the position of radio microphone, so as to avoid the radio in a launching station, and interfere with communication.

Attentions:

1. In the car with airbags, users do not put the radio on the scope that airbag deployment may involve. If the radio is in the scope of the area that the airbag deployment may involve, once the airbag quickly expanded, the radio may hurt people in the car.

2. In a potential explosive atmosphere environment or occasion, the radio must be closed unless the radio is through a special certification. In a potential explosive atmosphere, electrical sparks can cause explosion or fire.

3. Do not replace or charge the battery in the potential explosive atmosphere environment. When installing and removing the battery, it may cause the electric spark and lead to explosion.

4. In a place where is close to the blasting area or detonator area, users must first close the radio to avoid possible explosion.
5. Using the original or approved batteries.

6 if metal conductor such as jewelry, key or bead chain touches the exposed electrode of the battery, all batteries may cause damage or personal injury. Be careful with the battery that has been fully charged, especially when it is loaded into a pocket, wallet, or other metal container.

7 charging should be carried out in the environment of 5~40℃. If it is beyond the temperature range, the battery service life will be affected, at the same time it may be filled with under rated capacity.

8. To avoid problems caused by electromagnetic interference or electromagnetic compatibility, user should turn off the radio in the occasion with logo “intercom off”. Such as in hospitals or other places where using of health care equipment. When taking a plane, users should also close the radio according to the requirements.

 

From the communication service aspects, marine radio can be divided into public digital radio, the police radio, aviation radio, marine radio.

Marine radio, which is specially used for the communication on maritime navigation, is also called ship radio. Marine radio is particularly strong in profession, which can adapt to the harsh environment, wide range ship activity, large temperature vibration and the needs of global maritime safe navigation. The design of marine radio is very professional, and the working frequency is uniform. In accordance with the unified provisions of the international maritime communications, marine radio operating frequency TX ranges from 156.025MHz to 157.425MHz, RX ranging from 156.025MHz to 163.275MHz. Channel is divided into international channels, the United States channels, Canada channels, and 10 weather channels. The three kind of working channel is the standard of the three channels, each kind of marine radio is equipped with three standard versions. Users, according to the requirements of use, need to choose the different frequency while purchasing the marine radio. Some marine radio, in addition to the above frequency point, also kept 10 frequency points, which can be defined by the users themselves. It is easy for users to use within themselves. There are same frequency points different frequency points in marine radio. 

In order to meet the marine communication requirements, the structure design of marine radio should take the following factors fully into consideration, such as waterproof, anti salt fog, anti solar radiation and other factors. Excellent water resistance is the main indicator of marine radio. Some marine radio, also equipped with good and waterproof speaker, microphone battery. What’s more, good heat dissipation of marine radio is also a guarantee of long-term reliable work. In order to facilitate the operation, the marine radio panel control buttons and knob are not only with small number, but also have relatively large volume. The display is large, and the character display is clear, intuitive. Generally, marine radio’s function is relatively simple, practical, only to retain its original function. Excellent water resistance, salt fog resistance, strong and durable, high reliability, much working frequency are the characteristics of the machine radio. In accordance with the relevant provisions, the use right of marine radio on the ship must obtain the China Classification Society issued the "Certificate of Approval for Marine Products of China Classification Society". In addition, according to the provisions of the global maritime safety and security system standards (GMDSS). Ships sailing on the sea must be equipped with marine radio, which is based on the GMDSS standards, the quantity of marine radio according to the tonnage of the ship. The main purpose is to ensure the ship in emergency situations to be contacted. The marine radio, according to the GMDSS standards for the production, is orange, and the battery is lithium, which can support eight hours, to meet the requirements in the maritime distress for a long time work.