The BOOK about 2 way radios - Good Reading!

What area does two way radio mainly use for?

Two way radio is mainly used in public security, civil aviation, transportation, water conservancy, railway, manufacturing, construction and service industries. It is used for communication and command dispatch among group members to improve the efficiency of communication and improve the rapid response ability of dealing with emergencies. More and more people begin to use two way radio in travel, shopping after two way radio used in the civilian market.

Regular maintenance of two way radio

1.      Your two way radio maybe dirty after long-term used, especially the keypad, knob and radio body. Please remove the knob and clean with a mild detergent (Do not use strong corrosive chemicals). Clean the cabinet with a damp cloth. The use of chemicals such as detergents, alcohol, sprays or petroleum preparations may cause damage to the surface and enclosure of the two way radio.

2.      Handle gently, do not move the walkie-talkie by hand-held antenna.

3.      Please cover the radio with dust cover (if equipped) if you don’t use it.

Use safety precautions

1.      Do not put the radio on the airbag deployment may be involved in the range while you are in a car with airbags. If the radio is in the airbag deployment may involve the scope of the region, once the airbag to expand rapidly, walkie-talkie may be a great impact with the injury inside the car. If the radio is in the airbag deployment may involve the scope of the region, once the airbag to expand rapidly, walkie-talkie may be a great impact with the injury inside the car.

2.      Turn off the radio in a potentially explosive atmosphere or occasion, unless the walkie-talkie is through special authentication. In potentially explosive atmospheres, electrical sparks can cause an explosion or fire.

3.      Do not replace or charge the battery in potentially explosive atmospheres. Installation and removal of the battery may result in contact with the spark and cause an explosion.

4.      You must turn off the radio firstly, before near the blasting area and detonator in the area, so as not to cause a possible explosion.

Note on radio operation

1.      While the radio is transmitting, keep the radio in a vertical position, and keep the microphone 2.5-5 cm distance away from the mouth, at least 2.5 cm away from the head or body, at least 2.5 cm away from the human body.

2.      Do not switch off/on quite often while using, while adjusting the volume to fit your listening volume.

Precautions for battery use

1.      Use the original or approved battery.

2.      If the metal conductor such as jewelry, keys or beads touched the exposed electrodes of the battery, all batteries may cause damage or personal injury. Use caution when handling a charged battery, especially when handling it in a pocket, wallet, or other metal container.

3.      The charge should be 5 to 40 degrees in the environment. If this temperature range is exceeded, the battery life is affected, and it is possible to charge less than the rated capacity.

Precautions for Antenna Use

1.      Only use the original or approved antenna. Unauthorized antennas, modified or supplemented antennas may damage the radio or violate regulations of the Radio Regulatory Authority of the Ministry of Information Industry.

2.      Do not get the antenna by hand while using

3.      The radio antenna can’t be screwed off while using, or in the launch of the power tube is easy to burn out.

4.      Do not use the damaged antenna. While transmitting, if the damaged antenna touches the skin, it may cause minor burns.

Electromagnetic Interference / Electromagnetic Compatibility

To avoid problems caused by electromagnetic interference and / or electromagnetic compatibility, turn off the radio in the case of a "closed radio" logo. Such as hospitals or other occasions where health care medical equipment is used. In the plane, should also be required to turn off the radio.

Introduction to Digital Clustering

Digital cluster mobile communication system is a new generation of advanced professional radio command and dispatch system developed in the early 90s of the 20th century. Based on the analog cluster mobile communication system, the digital cluster mobile communication system adopts the most advanced digital technology and communication technology, which has the characteristics of advanced technology, high spectrum utilization rate and high data transmission rate. It integrates command and dispatch, telephone Interconnection, data transmission and short message communication and other advantages in one of the new generation of cluster communication technology. Digital cluster communication system is a dedicated command and dispatch system, the system channel using dynamic allocation, work for the simple and half-duplex mode, the network coverage area coverage, business focused on short-term wireless to wireless calls, business Users with priority and special features for group users and special user groups, belonging to the private network communication system. Digital cluster communication is developed on the basis of analog cluster communication. Digital cluster communication adopts digital processing in various key technologies such as signaling, multiple access mode, speech coding, modulation and demodulation, and channel control. Meanwhile, based on digital system, Features Combined with synchronization technology, error detection and error correction technology and diversity technology, the digital trunk communication with anti-interference ability, high-quality long-distance transmission, high security, high reliability and highly flexible service adaptability and peripheral interface connection Capacity, and other special features, and the entire digital cluster communication system capacity larger, more convenient system networking. Compared with the public network of the cellular mobile communication system, the professional network of the digital trunked mobile communication system emphasizes such functions as group call, general call, emergency call, forced disarming and different call priority levels; more emphasis on shortening the call establishment Time, especially in emergencies, hoping that a pass that is (less than 0.5s), otherwise it will cause very serious consequences; scheduling command requirements concise, the general talk time of tens of seconds. With the development of mobile communication technology, TETRA digital cluster mobile communication system has been developed under the background of the development of professional mobile communication system which can meet the demands of many different professional departments as much as possible.

Introduction to TETRA Technology

TETRA digital cluster mobile communication system is a kind of digital time division multiple access (TDMA) technology based wireless cluster mobile communication system. The system is a joint system of the ETSI (European Telecommunications Standards Association), manufacturers, testing departments and government departments, in order to meet the professional needs of European countries, the design of mobile communications, the development of a unified standard open system. TETRA digital cluster communication system can provide command dispatch, data transmission and telephone service on the same technology platform, it not only provides multi-group scheduling function, but also can provide short data information service, packet data service and digital full-duplex mobile phone service. TETRA digital trunked mobile communication system also supports a powerful mobile off-line through (DMO) approach, enabling authentication, air interface encryption and end-to-end encryption. TETRA digital trunked mobile communication system also has a virtual private network VPN function, you can make a physical network for multiple organizations are not related to service. TETRA digital cluster mobile communication system has abundant service functions, higher frequency utilization, high communication quality and flexible networking mode. Many new applications (such as vehicle positioning, image transmission, mobile Internet, database query) In the TETRA be achieved.

TETRA business functions

Wireless interface features Traffic channel is busy, the signaling channel can be used as a business letter to the use of base station failure weakening function Virtual private network authentication Air interface encryption End-to-end encryption Direct work mode Fast call establishment

TETRA business type

Basic service Subscriber service (single call, group call, telephone interconnection service) Bearer service (circuit mode data service, short data service, packet data service) Basic supplementary service Call type selection (single call, group call, Call) Area selection Priority call Preemptive priority call Late entry Dynamic reassembly Automatic retransmission Time-out call Out-of-service area indication Call display Caller / called party Display caller identification Caller identification display Unconditional call forwarding Busy call forwarding User can’t answer in time Transfer Non-Acknowledgment Transfer Abbreviated Addressing Dialing to a busy subscriber Completing a call to an unanswered call Completing a call barring Optional supplementary service station Verification Call screening Intercepting control Transfer billing

Technical terms

MONITOR

A listening mode to accept the weak signal using. Press the dedicated key to force the receiver signal channel, the operator with the ear to identify the faint sound of the speaker, to listen to the purpose.

Scanning (SCAN)

In order to hear all the channels of the call, and used a listening mode. By pressing the dedicated key, the receiving circuit in a certain order by a channel to receive a period of time to listen to the signal in the channel. If the time for each channel to receive 100ms, you can scan ten channels per second, the scanning speed of 10ch / s.

Priority Channel Scan

The set priority channel is preferentially scanned during scanning.

Delete / Add Scan Channel

Remove a channel from the scan list or add it to the scan list.

Voice-activated (VOX)

When the function is activated, you do not have to press the PTT button to start the transmission directly through the voice.

Time Out Timer (TOT)

This feature is used to limit the user in a channel over time transmission, but also to avoid long-time radio launch and cause damage.

Power saving function (Battery Save)

In order to save electricity, extend the standby time, the radio in a period of time without launch acceptance and key operation, will be shut down for some time, a period of time to start the work, this approach is called power saving. The switch-on time is approximately 1: 4. When receiving a signal or a key operation, the radio immediately exit the power-saving state, into the normal state.

High and low power select function (High / Low power)

This feature allows the user to select either high or low power depending on the situation.

Disable feature (Busy Channel Lockout)

When using this function, the user is prohibited from transmitting signals on a busy channel.

Squelch Level

The intensity of the noise in the received signal is corresponding to the strength of the signal, the stronger the signal is, the weaker the noise is. The maximum noise and minimum noise is divided into several files, each file is called a level. The files called squelch level. Users can choose according to the actual situation.

 

CTCSS / CDCSS functions

Use this feature to avoid receiving irrelevant calls.

2-TONE / DTMF selective call function

Use 2-TONE or DTMF signaling to select the appropriate intercom.

Reverse Frequency Function

When using the scrambling function, the transmission frequency and reception frequency of the radio are interchanged, and the set signaling is also interchanged.

Off-line function (Talk Around)

When the off-line function is used, the transmission frequency of the radio becomes the same as the reception frequency; the transmission signaling is also converted into the same as the reception signaling.

Auto-answer function (Auto-Transpond)

When the transceiver receives a correctly coded call, it sends a signal to the caller in response to the call.

Emergency Alarm (Emergency Alarm)

Press the special alarm key, the intercom to the maximum sound alarm or issue a predetermined alarm code to the other handset or base station.

Patrol Record

Patrol officers arrived at the patrol point, the radio will receive a patrol register issued by the query signal, and then automatically start the registration operation, the identity code and other information sent to the patrol register to be registered, indicating that a patrol has reached the place.

Key lock function

Use this function to prevent key error operation.

Battery Indicator

It shows the electric quantity.

Lighting function (Backlight)

For night or dim operation, you can see the LCD display and buttons.

Copy function (Cloning)

This feature allows data from one radio to be copied to other radios of the same model.

Modulation

Modulated signal with one or a few parameters to control the carrier parameters of the change, in accordance with the different control parameters, modulation can be divided into AM, FM and phase modulation.

Audio

Audio, refers to the human voice frequency, usually refers to 300Hz-3400Hz frequency band.

Carrier

Voice, digital signals and other useful signal carrier, easy to transmit high-frequency electromagnetic waves. Modulation signal with one or several parameters to control the carrier parameters of the change, in accordance with the different control parameters, modulation can be divided into AM, FM and phase modulation.

Channel and channel spacing

Channel refers to the frequency value occupied by transmitting and receiving. The frequency difference between adjacent channels is called the channel spacing. The prescribed channel spacing is 25 kHz (wide band), 20 kHz, 12.5 kHz (narrow band), and so on.

2-TONE

2-TONE, two tone signaling, composed of two audio signals, A Tone + B Tone. Start A Tone for a period of time, and then interval of time, then B Tone. The use of 2-TONE signaling can choose to call the corresponding walkie-talkie.

5-TONE

5-TONE, 5 tone signaling, the role of signaling with the same two, the difference is that the composition of the five frequencies.

CTCSS

CTCSS (Continuous Tone Controlled Squelch System), continuous voice control squelch system, commonly known as sub-audio, is a lower frequency than the audio frequency (67Hz-250.3Hz) attached to the audio signal transmission technology together. Because its frequency range below the standard audio, so called sub-audio. When the intercom for the received signal IF demodulation, the sub-audio signal through filtering, shaping, input to the CPU, and the machine set the CTCSS frequency to compare, to decide whether to turn on the mute.

CDCSS

CDCSS (Continuous Digital Controlled Squelch System), continuous digital control squelch system, its role and CTCSS the same, the difference is that it is a digital encoding as a mute is turned on condition.

DTMF

DTMF (Dual Tone Multiple Frequency), dual tone multi-frequency, by the high frequency group and low frequency group, high and low frequency group contains four frequencies. A high-frequency signal and a low-frequency signal superimposed to form a combined signal, representing a number. DTMF signaling has 16 codes. DTMF signaling can be used to select the appropriate call radio.


Economic: for mobile users, the use of walkie-talkie, the annual need to pay is the Frequency usage fee; the use of mobile phones, you need to pay is a call charge for each call. For the more frequent users, the comparison of the two costs, you can draw the conclusion of what is affordable . In addition, the world have set aside a free public band, the use of free public band radio, without the application, without paying royalties, making the use of walkie-talkie more economical.
Convenient: In the communication range, according to the frequency set by the radio, press the launch button to call, Set up Group Call as required, while achieving one or several people or more intercom, ideal for factory \ Property management \ construction and other aspects of use.
Suitable for the environment: the current mobile communication network and fixed telephone network, there are many areas that have not yet been covered, such as remote rural \ forest \ pastoral \ waters, need to add a walkie-talkie.

 


How the intercom works


For a radio to operate, a transmitter is required to transmit a signal and a receiver to receive the signal. In the transmitter, the microphone converts a voice signal into an electrical signal, because the electric signal is very weak, too low frequency, can not be sent too far. The transmitter processes and amplifies these audio signals into radio signals that are transmitted through the antenna into the air. Antennas receive radio signals, and then sent to the receiver, the receiver will convert these radio signals into the original audio signal, and then passed to the speaker, and then you can hear the original sound information. The transmitted signal and the received signal are converted by the antenna changeover switch. Both the transmitter and the receiver are powered.


Hand-held radio products


Hand-held radio is a small, portable walkie-talkie allows users to carry . In the machine's packaging generally include: Host: including transmitter \ receiver \ built-in microphone and speaker; Battery: provide walkie-talkie power, can generally provide Different capacity and specifications of the options; Antenna: receive and transmit radio signals, the antenna for the frequency band and host the same frequency band;


External ear microphone: Optional accessories, ear hanging or earplugs.

 


l  Antenna

l  Band switch knob

l  Indicator

l  Power switch and volume control knob

l  Speaker

l  Microphone

l  PTT button

l  Monitor button

l  External MIC / SP waterproof cover (with MIC / SP jack)

l  Belt clip

l  Battery

l  Battery clip

There are many antennas, such as rubber antenna, hand-held rod antenna, car sucker antenna, fiberglass omnidirectional antenna, Yagi directional antenna, ceiling antenna.

Now a lot of radio frequencies are the whole paragraph. There are 136-174M, 400-470M. Although some manufacturers claim that they antenna is the whole paragraph, but it is better to distinguish the frequency of the antenna.

It’s better to use 400 high antenna for the whole paragraph radio, the frequency is above 450Mhz; It’s better to use the 400 low antenna while the radio frequency is below 420Mhz. Pay more attention on it when the users need a larger communication distance range.

Ordinary rod antenna not works well, The length of the  rubber antenna is very important, is not the longer the better.

The price between high and low quality car sucker antenna is big. The former’s price is hundreds of yuan or even one thousand yuan, but the latter just cost 40 yuan. We suggest you to sell good quality, high sensitive antenna, it cost one hundred yuan about.

 

 Channel value

There are some walkie talkies with a display, while some ones not.

Normally the radios without display have 16 channels. For example, Motorola GP3188 is 4 channels, included 15 regular channels and one scanning channel.

There is 99 or 128 channels in the walkie talkie with display it means the walkie talkie can storage 99 or 128 groups frequencies max. Marine radio is 128 channels normally.

Indicator

The indicator light is different while the radio is  transmitting or receive. Generally, When the radio is not working, the indicator light is off. The light is red when it is transmitting and the light is green when receiving. While the received signal is not good, the green light is not always lit, but irregular jitter.

If the battery power is low, the red indicator light flashes to indicate that the battery is low, you should replace the battery, even though the radio is in standby mode. If you do not replace the battery in time, press the radio button will be "beep" long sound, and can not be used normally.

Speaker

There are some different caliber on walkie talkie speakers.

Normally the bigger walkie talkie sound is better than the smaller one, as the audio output power is higher.

Battery

The battery is an important part of the walkie talkie. The battery can be divided into: nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries by different properties. These batteries are explosion-proof battery. The ordinary batteries can not be used in flammable and explosive gas environment.

The battery above have their own strengths, The nickel-cadmium battery performance the strongest resistance to high and low temperature, lithium battery is the weakest.

In the part of toxicity, the most toxic is nickel-cadmium battery while lithium battery is relatively light.

In natural discharge, the battery self-discharge is about 15%, the general self-discharge of lithium batteries is least. The battery should be fully charged before storage, charge before the end of time, otherwise it will affect battery life.

Memory: nickel-cadmium battery is the strongest, it is best to use up and then recharge. Nickel-metal hydride batteries is second and the lithium-ion battery memory of the smallest. But it should also run out before charge, that’s mean it can not be reused when red light flashing, excessive use can damage the battery.

In the number of charge: nickel battery charge and discharge the least number of times and the lithium-ion battery is the most, generally up to 1000 times. In the sales of the walkie talkie, it is recommended that users should pay attention to the details of the charge, preferably with two batteries, a reasonable use of battery life of up to three years.

Charger

There are desktop charger and portable charging, there are many low-end 3.6V battery walkie talkie with a portable charger, but professional walkie talkie are equipped with a desktop charger. Many low-end factory do not use AC adapters to reduce costs, BAOFENG walkie talkie are equipped with AC adapters.

Charger can be set fast charge and slow charge, I suggest to use slow charge. Because the fast charge have fast damage to battery, charging the current fast charge but the charge of poor saturation dissatisfaction. Slow charge current is small, full of time to be longer but the saturation of the charge is higher.

Some walkie talkie can also be equipped with car charger, but it is not just plug in the car cigarette lighter to take power only. Such as Motorola and Kenwood and other brands also have a row of charge, while the battery can charge six simultaneously.

Headset and microphone

In general, walkie talkie external microphone have headphones, hand microphone, shoulder microphone. Headphones is divided from the way into wearing, ear-bud headphones, ear hanging headphones, headband headphones.

Headphones from the way with the intercom connection is divided into column and row type, column type is divided into single and double column, double column is divided into wide and narrow hole.

Headphones from call initiation mode is divided into air vibration type, skull vibration type, throat vibration type, ear bone vibration type.

The biggest difference between hand microphone and shoulder microphone  is that the former itself generally did not bring the speaker microphone but the shoulder microphone built-in speaker. Hand microphone and shoulder microphone is not only a call tool, sometimes built-in GPS and other peripherals.

The Operation Principle of Two Way Radio

 

1、Transmitter:

Phase-locked loop and voltage-controlled oscillator (VCO) generate the      transmitted RF carrier signal, after buffer amplification, excitation amplification and power amplifier will generate the rated radio-frequency power, which using the antenna low-pass filter to suppress harmonic components, then transit through the antenna.

2、Receiver:

Receiving part is the dual frequency conversion super-heterodyne mode. The signal inputted from antenna will magnify radio frequency through the transceiver conversion circuit and the band-pass filter, then through a band-pass filter into a mixing frequency, which mix the amplified signal from the radio frequency with the first local oscillator signal from the phase-locked loop frequency synthesizer circuit at the first mixer and generate a first intermediate frequency signal. The first intermediate frequency signal further eliminates the clutter signal of the adjacent channel through the crystal filter. The filtered first intermediate frequency signal enter into the intermediate frequency processing chip, then mix again with the second local oscillator signal to generate the second intermediate frequency signal, which filter unwanted spurious signals through a ceramic filter, then it was amplified and frequency discrimination to generate audio signal. Audio signal go through the amplification, band-pass filter, de-emphasis circuit, enter into the volume control circuit and magnify by power amplifier and drive speakers, then get the information people need.

3.Modulating Signal and Circuit:

The human voice convert to the audio signal by microphone, which enter into the voltage-controlled oscillator and modulate directly through amplifying circuit, pre-emphasis circuit and band-pass filter

4、Signaling Processing:

CPU generates CTCSS / DTCSS signal that was magnified and adjusted then, and enter into the voltage-controlled oscillator for modulation. After receiving the low frequency signal obtained by frequency discrimination, part of them process filter shaping through the amplification and band-pass filter of sub-band, then enter into the CPU, compared with the preset value, and the results will control the audio power amplifier and speaker output. That is, if same as the preset value, the speaker will turn on, and if it is different, the speaker is will turn off.

Using radio will have radiation problem or not

Radio design conforms with the relevant provisions of the [2001] 869 document issued by the Ministry of Information Industry , which will not harm the human body. Moreover, when using radio, it is not close to the human body, but away from the human body 5 to 7 cm.

Belows are several factors of affect radio’s conversation distance and effect

1、System Parameter:

1)The stronger the transmitter output power, the greater the coverage of the transmitted signal, the farther the communication distance. But the transmission power can not be too large, if it is too large, not only consuming electricity and impacting life of power amplifier components,also the interference is stronger, which will affect others communication effect. The larger transmission power also can produce radiation pollution. The regulation and administration of radio-services agency of every country has clear stipulation on the transmission power of communication device.

2)The higher the receiver sensitivity of the communication device, the farther the communication distance.

3)Antenna gain, when antenna match with radio , usually, the antenna height increases, the receiving or transmitting power enhance. Hand-held radio’s antenna always is helical, the bandwidth and gain is smaller than other types of antennas, and is more likely to influence by human impact.

2、Environmental Factor:

Environmental factors mainly have path, the density of trees, the environmental electromagnetic interference, buildings, weather conditions and terrain differences and so on. These factors and other parameters directly affect the electric field intensity and coverage area of signal.

3、Other Influence Factors:

1)Low battery power. When battery power is low, the conversation quality will get worse. When the problem gets more serious, it will make noise and affect the normal conversation.

2)Matched antenna. When antenna frequency band is inconsistent with radio band and antenna impedance not match, they will seriously affect the conversation distance. For users, the antenna should be tightened when using it. Besides,users can not freely use the antenna that provided by non-manufacturers,or antenna frequency is different with radio.

3)Tone quality is mainly determined by the pre-emphasis and de-emphasis circuit, there are more advanced voice processing circuit "applications of voice companding circuit and low-level expanding circuit", which have high fidelity effect on voice.

4) Factor of affecting the distance and effect of two way radio is also related to the season, summer is better than winter.

 


1、Housing:

Professional radio generally use a very good performance of the plastic material PC + ABS, which have good luster appearance and not easy to aging and wear, so make the products durable ; commercial radio always choose engineering plastics ABS, which can perfectly satisfy the requirements in appearance, strength, wear resistance and aging; keypad with silica gel have characteristics of wear resistance, non-aging and good hand feeling; aluminum housing with lightweight aluminum alloy ADC12, is easy to shape and subsequent processing.

2、Host:

Generally include housing,PTT button, headphone and power jack plug, PCB components, LCD parts, volume / switch button, coding knob, indicator, MIC and so on. Function of PTT button is to transmit switch, generally on the side.Indicators indicate the operating status, usually at the top. The top of radio also has volume / switch button and coding knob (select channel). LCD parts visually display the working status of radio. PCB components are the core of radio, the important components are on the PCB, non-professionals not allow to disassemble. Due to the requirements of technical performance and anti-drop , most of the radios have special shield, aluminum (fixed PCB) and so on. Besides, Professional radio have waterproof requirements and more complex structure.

3、Battery:

The battery is divided into Ni-Cd, Ni-MH and Li-ion batteries with capacities of 600mAh, 800mAh, 1100mAh, 1500mAh and so on. Li-ion battery costs are more expensive,so is still under the development stage. Ni-Cd and Ni-MH battery is more common, generally the large-capacity battery is recommend to using Ni-MH battery . Surface and the bottom shell are used ultrasonic welding, so they are solid and reliable.

4. Belt Clip:

The function is to fasten radio on the leather belt. To make it easier for consumers, belt clip can be detachable.

5、Antenna:

Divided into two parts of the antenna jacket and antenna core. Antenna jacket uses the high-performance TPU material, which have good performance of anti-bending and anti-aging ; antenna core generally uses thread construction and connects with the host, which is easy to disassemble.

6.  Desktop Charger:

Together with AC adapter to charge the battery or the whole radio. It’s Structure generally include DC socket, charging shrapnel, indicator light, keypad and so on. DC socket connects with the AC adapter, shrapnel connects with battery pole piece, indicator light indicates the charge status, the keypad is played the role of discharge. Desktop Charger generally can charge the battery and the whole radio.

In addition,the two way radio also have leather case and headphone and other accessories.

 

 

Interphone operate principle and function introduction


Frequency and Spectrum:

 The electromagnetic spectrum is the sum of all frequencies of electromagnetic radiation, ranging from the longest radio waves to the shortest cosmic rays. The spectrum can be divided into parts, called frequency bands. The electromagnetic spectrum is divided into the following frequency bands:


 100Hz 300KHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz


 AM  Amplitude Broadcasting  MW  medium wave    SW Shortwave   HF high frequency


 VHF Very High Frequency  UHF Ultra High Frequency  SHF Super High Frequency          EHF  Extremely High Frequency


 Interphone use of the band:


 VHF 136-174MHz, is divided into two sections: 136-150MHz, 150-174MHz

 UHF 350-370MHz  & 370-400MHz &  400-470MHz  450-520MHz


 Radio frequency band characteristics:


 The atmosphere around the earth will attenuate and refract radio signals, as it attenuates and refracts light. The usual rule is that the lower the frequency, the smaller the attenuation loss is: Ground wave propagation (radio below 300KHz (30MHz-900MHz most suitable for wireless walkie-talkie communication) Noise: electromagnetic noise from the machine and the engine, because the noise signal (the frequency range of the radio frequency of the radio frequency) The frequency of low-frequency signals, therefore, the low-frequency signal is more sensitive to noise.Transfer distance: in rural and suburban VHF transmission distance of the largest urban UHF transmission distance in the largest.


Principle Overview:

 1、Transmitter:

Phase-locked loop and voltage-controlled oscillator (VCO) generate the transmitted RF carrier signal, after buffer amplification, excitation amplification and power amplifier will generate the rated radio-frequency power, which using the antenna low-pass filter to suppress harmonic components, then transit through the antenna.

2、Receiver:

Receiving part is the dual frequency conversion super-heterodyne mode. The signal inputted from antenna will magnify radio frequency through the transceiver conversion circuit and the band-pass filter, then through a band-pass filter into a mixing frequency, which mix the amplified signal from the radio frequency with the first local oscillator signal from the phase-locked loop frequency synthesizer circuit at the first mixer and generate a first intermediate frequency signal. The first intermediate frequency signal further eliminates the clutter signal of the adjacent channel through the crystal filter. The filtered first intermediate frequency signal enter into the intermediate frequency processing chip, then mix again with the second local oscillator signal to generate the second intermediate frequency signal, which filter unwanted spurious signals through a ceramic filter, then it was amplified and frequency discrimination to generate audio signal. Audio signal go through the amplification, band-pass filter, de-emphasis circuit, enter into the volume control circuit and magnify by power amplifier and drive speakers, then get the information people need.

3、Modulating Signal and Circuit:

The human voice convert to the audio signal by microphone, which enter into the voltage-controlled oscillator and modulate directly through amplifying circuit, pre-emphasis circuit and band-pass filter

4、Signaling Processing:

CPU generates CTCSS / DTCSS signal that was magnified and adjusted then, and enter into the voltage-controlled oscillator for modulation. After receiving the low frequency signal obtained by frequency discrimination, part of them process filter shaping through the amplification and band-pass filter of sub-band, then enter into the CPU, compared with the preset value, and the results will control the audio power amplifier and speaker output. That is, if same as the preset value, the speaker will turn on, and if it is different, the speaker is will turn off.


 Commonly used to explain:


Carrier: voice, digital signals, signaling and other useful signal carrier, easy to transmit high-frequency electromagnetic waves.

Frequency: The total number of cycles per second, such as alternating current or radio waves, usually measured in Hertz.

Channel: Channel refers to the frequency value occupied when transmitting and receiving.

Channel spacing: refers to the frequency difference between adjacent channels is called channel spacing. There are 25KHz (wide band), 20KHz, 12.5KHz (narrowband) among the prescribed channels.

Simplex: At the same time, only in one direction to send information, can be divided into the same frequency and simplex simplex two ways.

PTT: Push To Talk abbreviation, press the call, then enter the radio-like radio.

Audio: Audio, refers to the human voice frequency, usually refers to 300Hz-3400Hz frequency band.

Modulation: Modulate the signal of one or several parameters to control the carrier parameters of the change, in accordance with the different control parameters, modulation can be divided into amplitude modulation, frequency modulation and phase modulation.

Coverage: refers to the degree of confidence we have in estimating the state of communication in a given area. A certain radio can talk within 90% of the time and 90% of the coverage within the coverage area.

Squelch: The squelch circuit is used to reduce or eliminate unwanted signals and noise before reaching the speaker. There are two types of squelch: carrier squelch and code squelch.

Carrier Squelch: Often referred to as noise-compensated squelch, it is used to prevent noise from being heard from the loudspeaker when no information is being transmitted.

Coding Squelch: allows the listener to receive only the information sent to them, only when the received information with a pre-determined code will open the speaker, there are two common squelch code: Tone encoding squelch (CTCSS , PL 38/42 group), digital coding squelch (DPL, DTCSS 84 group)

Antenna: A device specially designed to transmit radio signals and transmit such signals to the atmosphere. This signal can be transmitted much affected by many factors, including antenna plays a major role.

MONITOR: A listening mode used to hear weak signals. By pressing the dedicated key to force the receive signal channel, the operator recognizes the weak sound in the SPK with the ear to achieve the purpose of listening.

Scan (SCAN): In order to hear all the channels of the call, and used a listening mode. By pressing the dedicated key, the receiving circuit in a certain order by a channel to receive a period of time to listen to the signal in the channel. If the time for each channel to receive 100ms, you can scan ten channels per second, the scanning speed of 10ch / s.

Voice Control (VOX): voice control function, through the launch operation can start the voice, the sound transmission out. You do not have to press the PTT key. Stop talking, the launch also stops.

Low voltage alarm: When the battery voltage reaches the preset low voltage value, the intercom will have indicator light flashing and the alarm beep sounded to inform the user should replace the battery or charge the battery.

Power saving function: to save electricity, extend the standby time, the radio in a period of time without launch and key operation, will be shut down for some time, a period of time to boot the work, this approach is called power saving. The switch-on time is approximately 1: 4. When receiving a signal or a key operation, the radio immediately exit the power-saving state, into the normal state.

Squelch Series: the strength of the received signal noise and the strength of the signal was the corresponding relationship, the stronger the signal the stronger the noise. The maximum noise and minimum noise is divided into several files, each file is called a level. Divided into the number of files called squelch series.

Tone elimination: the call, the PTT button to launch the release of the launch, the receiving side will hear the harsh "Cha ..." sound, called the tail. To eliminate this sound, can use some special techniques for processing.

Other: lighting, lock keys, eliminate noise channels, and so on.

 

I hope you enjoyed today, reading up on this radio text information file on our web site, hoping it will educate and inform better choices when purchasing 2 way communication radios!!

 

 

 

 

 

 

 

 

 

 

 

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