I. Introduction
With the promotion of China's "harmonious society construction" and radio and television "village-to-village" projects, after several decades of development of FM radio, basically every county has built FM radio stations to achieve coverage of broadcast signals in the region. But the number of radios owned by farmers is small, and the real broadcast signal to the home and the listening rate is very low. In the 1960s and 1970s, rural broadcasting had a good network foundation and management institutions. Basically, households had small speakers, and rural areas had “amplification stationsâ€. But then with the popularity of television, the broadcast gradually faded out of our horizons. Historically, broadcasting has a good mass base in rural areas, and even in today's society where information is highly developed, there is a great demand. At present, some places in China are gradually recovering rural broadcasting, as the assessment content of the new rural construction and the “village-to-village†project.
Under the current technical conditions, the method used to achieve the restoration of rural broadcasting is a problem faced by the government and the broadcasting and television authorities: whether to re-erect the barbed wire, or to use the existing cable TV network, telephone network, wireless FM network to achieve coverage of rural broadcasting? Let's take the SCA wireless FM broadcasting system of Beijing Hengxing Ketong Technology Development Co., Ltd. as an example to make a brief analysis on how to use the existing wireless FM broadcasting system to realize rural broadcasting.
Second, the introduction of frequency modulation subchannel (SCA) addressable technology
Wireless FM broadcasting is a method of adopting FM modulation of a broadcast signal, and modulating an audio signal onto an FM carrier of 87---108 MHz, converting a broadcast signal into a radio signal through an FM transmitter and a transmitting antenna, performing wireless transmission, and receiving A broadcast method that is listened to by an FM radio or a dedicated FM receiving device.
The SCA addressable control technology utilizes the SCA subchannel in the FM broadcast baseband (the 67KHz used as the subcarrier of the additional channel in China), and uses the FSK digital modulation method to implement the broadcast addressing function, that is, the addressing. The information is modulated by the frequency modulation method with a certain frequency offset (for the stereo broadcast, the maximum frequency offset of the modulation is 10% of the total frequency offset of the FM broadcast) to the primary carrier (ie, the FM broadcast frequency), and is transmitted along with the broadcast signal. The block diagram of the SCA addressable system control transmission part is shown in the figure below, and the reception is the inverse transform of the transmission.
figure 1
Third, the working principle of the system and the introduction of major equipment
1, the workflow: addressing information is through the computer serial port (RS-232) output digital signal, this digital stream is controlled by the intelligent broadcast master control software. The computer RS-232 serial port is connected with the HX-2500SCA digital encoder. The digital encoder uses the FSK digital modulation technology to modulate the signal to the 67KHz carrier. The 67KHz carrier is used as the FM broadcast subcarrier signal and is sent to the transmitter and audio. The signals are modulated together and amplified by the transmitter power amplifier and transmitted to space for propagation.
After receiving the RF carrier, the receiving end will automatically demodulate the SCA signal and the stereo audio signal. The audio signal is amplified to drive the speaker, and the SCA signal is sent to the decoding circuit and the relay to execute the switch command. Address function.
2. System composition: The system is mainly composed of HX-6000 main control software, HX-2500SCA subchannel encoder, FM70 FM sound column, FM4210 FM receiver controller, FM4310 FM receiver and other equipment, the following for each device The functions and technical parameters are described in detail.
==============
3. Introduction to major equipment
3.1, the system is mainly controlled by HX-6000
figure 2
HX-6000 digital multi-channel intelligent broadcasting system software is a new generation of intelligent broadcasting software independently developed by Beijing Hengxing Ketong Technology Development Co., Ltd. with independent intellectual property rights. Independently develop the playback engine, one computer can simultaneously output 1-6 channels of audio broadcast programs, and point-to-point addressing control. The software has obtained the "Computer Software Copyright Registration Certificate".
image 3
The software has terminal address and receive channel initialization, remote control terminal frequency and volume. Arbitrary partition grouping, addressing control function, multi-channel playback, emergency broadcast, external device timing switch, power timer switch, database backup and restore, automatic execution of playback tasks, automatic power on/off, etc. Play the software.
The software can be used for school language and teaching management activities such as foreign language teaching, music ringing, educational management, campus broadcasting, etc. It can also be applied to background music in rural radio, tourist attractions, industrial and mining enterprises, troops, institutions, communities and other places. Autoplay.
System hardware requirements: 586 or more computers, 32M or more memory
Operating system requirements: Windows95/98/2000/NT/XP or higher
=================
3.2, HX-2500SCA subchannel encoder
Figure 4
Features
The HX-2500SCA subchannel digital encoder is the key processing device for the control and data coding conversion and transmission of the intelligent frequency modulation system. It uses the frequency shift keying (FSK) method to change the digital control signal into an analog carrier, and mixes it into the SCA subchannel transmission of the FM broadcast. The control signal does not occupy the frequency point alone, which saves the frequency resources. The code modulator adopts DDS technology for direct frequency modulation, and has the characteristics of clean spectrum, accurate frequency without drift, occupying small bandwidth, and ensuring low error of the receiving end. The transmission channel is transparent and can be used with our intelligent FM system. It can also be used for medium and low speed data transmission. The main features are as follows:
ï¬ Support RS-485 and RS-232 control mode input;
ï¬ Data communication rate can reach 2400bit/s;
ï¬ Signal digital processing is strict, the waveform phase is accurate and error-free;
ï¬4th-order active filter to ensure no interference to the sound channel
ï¬ The signal transmission radius is basically equal to the broadcast coverage;
Technical indicators
Project technical parameter project technical parameter data modulation mode FSK carrier output amplitude 0-3VPP continuously adjustable carrier operating frequency 67K/70KHZ output impedance 600 ohm, Unbalanced
Carrier operating bandwidth PS working environment conditions -20 ~ +65 ° C
Out-of-band residual <45DB operating voltage AC220V/50Hz
Modulation data rate 2400bit power <5W
Data interface RS232, RS485 installation 1U cabinet
3.3, FM75 FM sound column
Features
FM75 outdoor FM sound column is a professional FM radio receiving equipment, which integrates FM receiving, power amplifier and speaker. It adopts aluminum alloy integrated structure, beautiful appearance, outdoor rainproof design, receiving circuit adopts SMT patch technology, PHILIPS Professional equipment I2C. The unique SCA anti-interpolation design automatically shuts down when there is no carrier transmission signal or wireless interference. Support HX-6000 software remote control switch machine, automatic fixed-point time broadcast, up to 2040 independent ID codes, support online address modification. It is the preferred equipment for rural broadcasting, scenic spot broadcasting, and campus broadcasting. It can be customized to carrier control type, SCA anti-interpolation type, point-to-point addressable type, or can be customized to double-point frequency priority switching.
â— Modular design, easy to repair â— PLL digital frequency synthesis, frequency accuracy, no frequency drift â— Addressable control or carrier automatic switch control â— Beautiful sound quality, volume can be adjusted separately â— Ultra low energy design, small standby current â—Outdoor waterproof and anti-corrosion design, suitable for light pole and wall suspension installation â— Suitable for wired closed circuit transmission, or can be customized for wireless reception
Figure 5
Project technical parameters project technical parameters model outdoor type FM75 squelch turn-on level 30dBu
Frequency user specified 82.5-108MHZ, single point frequency receiving rated output power 10W/25W/35W/50W
Frequency long-term stability 15PPm Power supply mode 220V±20%/60V±10%
Frequency accuracy -30°C～+60°C<1KHz Function and structure Aluminum alloy integrated structure Rated input level (FM) 35±5dBu Dimensions 40×200×350
3.4, FM4210 FM Receiver Controller
Figure 6
Features
The FM4210 FM receiving controller is a terminal control device for FM intelligent broadcasting system. It adopts microcomputer-controlled frequency synthesis phase-locked PLL technology and PHILIPS latest I2C. It has the advantages of high frequency stability, high audio index and convenient operation. It can demodulate FM signal into standard audio signal, and realize local CD, deck audio input, MIC local sound reinforcement, etc., and has a set of 220V AC controlled power output for managing external devices such as audio amplifiers. Switch on and off. It can be widely used in rural radio, campus FM radio, shopping malls, supermarkets and other FM signal demodulation, and can also be used for broadcast radio room monitoring.
â— Carrier level automatic switch machine or SCA remote addressable switch machine
â— Output power automatic control function for use by modulator or amplifier
â— Panel touch switch control with LED level display, volume display, etc.
â— FM, AUX, MIC panel selection switch, using professional audio switching chip
â— 82.5~108MHz full-band demodulation, audio frequency stepping 0.1MHz continuously adjustable
â— With SCA independent output, RS-232 interface for transmitting digital signals (such as LED screen)
â— SCA subcarrier control signal demodulation, accurate and stable, low bit error rate (SCA type has)
â—Using a 19-inch standard chassis, 2U height, aluminum brushed panel, beautiful appearance
â— Built-in 1W monitor speaker, monitor volume can be monotonous, convenient for local audio or radio monitor
Technical indicators
Technical parameters of the project Technical parameters Frequency range 82.5-108MHz, continuous adjustable selectivity 400KHz >60dB
Frequency accuracy 1.5×10-6MHz RF input terminal metric F head, 75 ohm working level 40-50dBμ Audio output terminal unbalanced RCA mono 1 set 1.0V (adjustable)
Signal to noise ratio 55dB power supply mode AC 220V ± 15%
Harmonic distortion (1KHz) 1% power control power ≤500W
Frequency response 80Hz-10KHz (±1.5dB) RS-232 output definition See the manual stereo separation 40dB monitor speaker power 1W
==================================
3.5, FM4310 multi-function frequency modulation and expansion machine
Features
FM4310 frequency modulation and expansion machine adopts PLL microcomputer to control frequency synthesis phase-locked loop technology, combined with PHILIPS latest demodulation IC, which has the advantages of high frequency stability, good audio index and convenient operation. It has carrier control type and SCA digital code addressable type, and supports remote software switch machine management control. Light touch panel control, with FM, LINE, MIC three input options, two-channel LED column level dynamic display, can be used for village broadcast room FM radio signal receiving amplification, direct drive tweeter. â— PLL phase-locking technology, 82.5-108MHz automatic electric tuning, manual automatic search â— LED digital frequency, volume, ID address display, column level dynamic display â— Light touch panel button switch, LED status display, easy to operate, user-friendly Design â— With remote superior broadcast priority function, remote lock interactive operation â— fixed resistance, constant pressure multi-mode output, suitable for matching constant pressure fixed-resistance speaker type tweeter
Technical indicators
Project technical parameters Project technical parameters Output impedance 4-16 ohms/70V/110V Constant voltage frequency range 82.5-108 MHz, frequency synthesis rated output power 50W/100W/150W (RMS, 8Ω) Frequency accuracy 1.5×10-6<1KHZ
Frequency response 50Hz-15KHz FM input level 35dBμ-60dBμ/75 ohm RF input terminal metric F head, 75 ohm line input 47K/0dBm
Power supply mode AC 220V ± 15% microphone input 600 ohms
Fourth, the technical points of installation and commissioning
At present, the FM transmitters (FM exciters) produced by FM transmitter manufacturers at home and abroad all have SCA subchannel interfaces (such as: RVR, Beiguang, Chengguang, Zhongchuan, Kaiteng Sifang, Tsinghua Yoshizhao, etc.). Under the existing radio transmitter, the SCA signal can be transmitted without any modification. The specific connection block diagram is as follows:
Figure 7
Key technology of installation and debugging: After the SCA signal is sent to the exciter, the modulation degree cannot be greater than 10% of the total frequency offset. If the SCA modulation is too large, it will interfere with the audio signal of the primary channel, resulting in degradation of the audio signal; if the SCA modulation is too small, the SCA decoding error rate will be high. Therefore, we must pay attention to the debugging of modulation degree in debugging.
==========
Five, engineering examples
The Chengde County Broadcasting and Television Bureau of Hebei Province resumed the FM radio transmission in May 2009. At the same time as the FM radio broadcast was resumed, the FM sound column was installed in the main trunk roads and squares of the county, and the broadcasting of the county town was realized at a fixed time. The specific implementation method is as follows:
The predecessor of Chengde County People's Broadcasting Station was the Chengde County Broadcasting Station. On November 8, 1988, the station was officially established. Two broadcast transmission points were set up in the county towns of Nanshan and Daheishan, with a transmission frequency of 98.5 MHz. The county Nanshan signal mainly covers the surrounding areas of the county and the southern villages. The Daheishan signal mainly covers the middle and northern villages of the county, as well as some areas such as Chengde urban area, paddock, Fengning and Longhua.
In 1992, the Chengde County Broadcasting and Television Bureau began to build a cable TV network. In 1994, a cable television station was established. In 2002, radio stations were stopped due to various factors. In August 2007, the Chengde County Bureau set out to resume radio broadcast work, re-apply and get approved for use at frequencies of 91.3 MHz and 92.8 MHz. The official launch began on April 24, 2009, and the broadcast time is 15 hours and 30 minutes. The broadcast began at 6:30 in the morning and ended at 10 in the evening. In addition to broadcasting the news programs of the central, provincial and municipal radio stations, it also mainly runs the county's news programs, social news programs, information programs and audience hotline live programs. Make full use of the telephone platform, SMS platform and Internet platform to achieve interactive communication with the audience.
At the same time that the wireless FM radio signal was opened, Chengde County Radio and Television Bureau purchased 40 FM75-25W FM sound columns from Beijing Hengxing Ketong Technology Development Co., Ltd., and installed them in the main roads and squares of the county. Every day, in the morning, in the middle and in the evening, the FM sound column is turned on, and the broadcast signal covers the whole county, so that the long-lost broadcast sound returns to the people's side, greatly improving the cultural life level of the urban people, and is warmly welcomed and praised by the masses.
Chengde County People's Broadcasting Station will give full play to the advantages and characteristics of radio waves. It plans to use the wireless transmission method to install FM transmitters and tweeters in each administrative village of the county to realize the rural village "village ringing". The voice of the party and the government is transmitted to thousands of families. At the same time, we must gradually apply high-tech means, from a single audio media to multimedia, through multimedia to the TV, in the future will also be sent to the computer through the Internet, to achieve all-round publicity, to create mainstream, strong media in Chengde County, The county government and the people's government serve the people.
Sixth, the conclusion
The use of existing FM radio transmitters to implement addressable urban broadcasting and rural broadcasting is currently the best solution for achieving broadcast coverage. With wireless broadcasting, neither cumbersome wiring nor dedicated line maintenance is required, and point-to-point addressable broadcasting can be realized. In the event of an emergency, emergency evacuation, emergency command, etc. can be implemented and no secondary investment is required. The transmission of emergency broadcast signals can be realized on the basis of the original FM transmitter. Therefore, the extension based on existing FM transmitters is the preferred solution for rural broadcast coverage.
I. Introduction
With the promotion of China's "harmonious society construction" and radio and television "village-to-village" projects, after several decades of development of FM radio, basically every county has built FM radio stations to achieve coverage of broadcast signals in the region. But the number of radios owned by farmers is small, and the real broadcast signal to the home and the listening rate is very low. In the 1960s and 1970s, rural broadcasting had a good network foundation and management institutions. Basically, households had small speakers, and rural areas had “amplification stationsâ€. But then with the popularity of television, the broadcast gradually faded out of our horizons. Historically, broadcasting has a good mass base in rural areas, and even in today's society where information is highly developed, there is a great demand. At present, some places in China are gradually recovering rural broadcasting, as the assessment content of the new rural construction and the “village-to-village†project.
Under the current technical conditions, the method used to achieve the restoration of rural broadcasting is a problem faced by the government and the broadcasting and television authorities: whether to re-erect the barbed wire, or to use the existing cable TV network, telephone network, wireless FM network to achieve coverage of rural broadcasting? Let's take the SCA wireless FM broadcasting system of Beijing Hengxing Ketong Technology Development Co., Ltd. as an example to make a brief analysis on how to use the existing wireless FM broadcasting system to realize rural broadcasting.
Second, the introduction of frequency modulation subchannel (SCA) addressable technology
Wireless FM broadcasting is a method of adopting FM modulation of a broadcast signal, and modulating an audio signal onto an FM carrier of 87---108 MHz, converting a broadcast signal into a radio signal through an FM transmitter and a transmitting antenna, performing wireless transmission, and receiving A broadcast method that is listened to by an FM radio or a dedicated FM receiving device.
The SCA addressable control technology utilizes the SCA subchannel in the FM broadcast baseband (the 67KHz used as the subcarrier of the additional channel in China), and uses the FSK digital modulation method to implement the broadcast addressing function, that is, the addressing. The information is modulated by the frequency modulation method with a certain frequency offset (for the stereo broadcast, the maximum frequency offset of the modulation is 10% of the total frequency offset of the FM broadcast) to the primary carrier (ie, the FM broadcast frequency), and is transmitted along with the broadcast signal. The block diagram of the SCA addressable system control transmission part is shown in the figure below, and the reception is the inverse transform of the transmission.
figure 1
Third, the working principle of the system and the introduction of major equipment
1, the workflow: addressing information is through the computer serial port (RS-232) output digital signal, this digital stream is controlled by the intelligent broadcast master control software. The computer RS-232 serial port is connected with the HX-2500SCA digital encoder. The digital encoder uses the FSK digital modulation technology to modulate the signal to the 67KHz carrier. The 67KHz carrier is used as the FM broadcast subcarrier signal and is sent to the transmitter and audio. The signals are modulated together and amplified by the transmitter power amplifier and transmitted to space for propagation.
After receiving the RF carrier, the receiving end will automatically demodulate the SCA signal and the stereo audio signal. The audio signal is amplified to drive the speaker, and the SCA signal is sent to the decoding circuit and the relay to execute the switch command. Address function.
2. System composition: The system is mainly composed of HX-6000 main control software, HX-2500SCA subchannel encoder, FM70 FM sound column, FM4210 FM receiver controller, FM4310 FM receiver and other equipment, the following for each device The functions and technical parameters are described in detail.
==============
3. Introduction to major equipment
3.1, the system is mainly controlled by HX-6000
figure 2
HX-6000 digital multi-channel intelligent broadcasting system software is a new generation of intelligent broadcasting software independently developed by Beijing Hengxing Ketong Technology Development Co., Ltd. with independent intellectual property rights. Independently develop the playback engine, one computer can simultaneously output 1-6 channels of audio broadcast programs, and point-to-point addressing control. The software has obtained the "Computer Software Copyright Registration Certificate".
image 3
The software has terminal address and receive channel initialization, remote control terminal frequency and volume. Arbitrary partition grouping, addressing control function, multi-channel playback, emergency broadcast, external device timing switch, power timer switch, database backup and restore, automatic execution of playback tasks, automatic power on/off, etc. Play the software.
The software can be used for school language and teaching management activities such as foreign language teaching, music ringing, educational management, campus broadcasting, etc. It can also be applied to background music in rural radio, tourist attractions, industrial and mining enterprises, troops, institutions, communities and other places. Autoplay.
System hardware requirements: 586 or more computers, 32M or more memory
Operating system requirements: Windows95/98/2000/NT/XP or higher
=================
3.2, HX-2500SCA subchannel encoder
Figure 4
Features
The HX-2500SCA subchannel digital encoder is the key processing device for the control and data coding conversion and transmission of the intelligent frequency modulation system. It uses the frequency shift keying (FSK) method to change the digital control signal into an analog carrier, and mixes it into the SCA subchannel transmission of the FM broadcast. The control signal does not occupy the frequency point alone, which saves the frequency resources. The code modulator adopts DDS technology for direct frequency modulation, and has the characteristics of clean spectrum, accurate frequency without drift, occupying small bandwidth, and ensuring low error of the receiving end. The transmission channel is transparent and can be used with our intelligent FM system. It can also be used for medium and low speed data transmission. The main features are as follows:
ï¬ Support RS-485 and RS-232 control mode input;
ï¬ Data communication rate can reach 2400bit/s;
ï¬ Signal digital processing is strict, the waveform phase is accurate and error-free;
ï¬ 4th-order active filter to ensure no interference to the sound channel
ï¬ The signal transmission radius is basically equal to the broadcast coverage;
Technical indicators
Project technical parameter project technical parameter data modulation mode FSK carrier output amplitude 0-3VPP continuously adjustable carrier operating frequency 67K/70KHZ output impedance 600 ohm, Unbalanced
Carrier operating bandwidth PS working environment conditions -20 ~ +65 ° C
Out-of-band residual <45DB operating voltage AC220V/50Hz
Modulation data rate 2400bit power <5W
Data interface RS232, RS485 installation 1U cabinet
3.3, FM75 FM sound column
Features
FM75 outdoor FM sound column is a professional FM radio receiving equipment, which integrates FM receiving, power amplifier and speaker. It adopts aluminum alloy integrated structure, beautiful appearance, outdoor rainproof design, receiving circuit adopts SMT patch technology, PHILIPS Professional equipment I2C. The unique SCA anti-interpolation design automatically shuts down when there is no carrier transmission signal or wireless interference. Support HX-6000 software remote control switch machine, automatic fixed-point time broadcast, up to 2040 independent ID codes, support online address modification. It is the preferred equipment for rural broadcasting, scenic spot broadcasting, and campus broadcasting. It can be customized to carrier control type, SCA anti-interpolation type, point-to-point addressable type, or can be customized to double-point frequency priority switching.
â— Modular design, easy to repair â— PLL digital frequency synthesis, frequency accuracy, no frequency drift â— Addressable control or carrier automatic switch control â— Beautiful sound quality, volume can be adjusted separately â— Ultra low energy design, small standby current â—Outdoor waterproof and anti-corrosion design, suitable for light pole and wall suspension installation â— Suitable for wired closed circuit transmission, or can be customized for wireless reception
Figure 5
Project technical parameters project technical parameters model outdoor type FM75 squelch turn-on level 30dBu
Frequency user specified 82.5-108MHZ, single point frequency receiving rated output power 10W/25W/35W/50W
Frequency long-term stability 15PPm Power supply mode 220V±20%/60V±10%
Frequency accuracy -30°C～+60°C<1KHz Function and structure Aluminum alloy integrated structure Rated input level (FM) 35±5dBu Dimensions 40×200×350
3.4, FM4210 FM Receiver Controller
Figure 6
Features
The FM4210 FM receiving controller is a terminal control device for FM intelligent broadcasting system. It adopts microcomputer-controlled frequency synthesis phase-locked PLL technology and PHILIPS latest I2C. It has the advantages of high frequency stability, high audio index and convenient operation. It can demodulate FM signal into standard audio signal, and realize local CD, deck audio input, MIC local sound reinforcement, etc., and has a set of 220V AC controlled power output for managing external devices such as audio amplifiers. Switch on and off. It can be widely used in rural radio, campus FM radio, shopping malls, supermarkets and other FM signal demodulation, and can also be used for broadcast radio room monitoring.
â— Carrier level automatic switch machine or SCA remote addressable switch machine
â— Output power automatic control function for use by modulator or amplifier
â— Panel touch switch control with LED level display, volume display, etc.
â— FM, AUX, MIC panel selection switch, using professional audio switching chip
â— 82.5~108MHz full-band demodulation, audio frequency stepping 0.1MHz continuously adjustable
â— With SCA independent output, RS-232 interface for transmitting digital signals (such as LED screen)
â— SCA subcarrier control signal demodulation, accurate and stable, low bit error rate (SCA type has)
â—Using a 19-inch standard chassis, 2U height, aluminum brushed panel, beautiful appearance
â— Built-in 1W monitor speaker, monitor volume can be monotonous, convenient for local audio or radio monitor
Technical indicators
Technical parameters of the project Technical parameters Frequency range 82.5-108MHz, continuous adjustable selectivity 400KHz >60dB
Frequency accuracy 1.5×10-6MHz RF input terminal metric F head, 75 ohm working level 40-50dBμ Audio output terminal unbalanced RCA mono 1 set 1.0V (adjustable)
Signal to noise ratio 55dB power supply mode AC 220V ± 15%
Harmonic distortion (1KHz) 1% power control power ≤500W
Frequency response 80Hz-10KHz (±1.5dB) RS-232 output definition See the manual stereo separation 40dB monitor speaker power 1W
==================================
3.5, FM4310 multi-function frequency modulation and expansion machine
Features
FM4310 frequency modulation and expansion machine adopts PLL microcomputer to control frequency synthesis phase-locked loop technology, combined with PHILIPS latest demodulation IC, which has the advantages of high frequency stability, good audio index and convenient operation. It has carrier control type and SCA digital code addressable type, and supports remote software switch machine management control. Light touch panel control, with FM, LINE, MIC three input options, two-channel LED column level dynamic display, can be used for village broadcast room FM radio signal receiving amplification, direct drive tweeter. â— PLL phase-locking technology, 82.5-108MHz automatic electric tuning, manual automatic search â— LED digital frequency, volume, ID address display, column level dynamic display â— Light touch panel button switch, LED status display, easy to operate, user-friendly Design â— With remote superior broadcast priority function, remote lock interactive operation â— fixed resistance, constant pressure multi-mode output, suitable for matching constant pressure fixed-resistance speaker type tweeter
Technical indicators
Project technical parameters Project technical parameters Output impedance 4-16 ohms/70V/110V Constant voltage frequency range 82.5-108 MHz, frequency synthesis rated output power 50W/100W/150W (RMS, 8Ω) Frequency accuracy 1.5×10-6<1KHZ
Frequency response 50Hz-15KHz FM input level 35dBμ-60dBμ/75 ohm RF input terminal metric F head, 75 ohm line input 47K/0dBm
Power supply mode AC 220V ± 15% microphone input 600 ohms
Fourth, the technical points of installation and commissioning
At present, the FM transmitters (FM exciters) produced by FM transmitter manufacturers at home and abroad all have SCA subchannel interfaces (such as: RVR, Beiguang, Chengguang, Zhongchuan, Kaiteng Sifang, Tsinghua Yoshizhao, etc.). Under the existing radio transmitter, the SCA signal can be transmitted without any modification. The specific connection block diagram is as follows:
Figure 7
Key technology of installation and debugging: After the SCA signal is sent to the exciter, the modulation degree cannot be greater than 10% of the total frequency offset. If the SCA modulation is too large, it will interfere with the audio signal of the primary channel, resulting in degradation of the audio signal; if the SCA modulation is too small, the SCA decoding error rate will be high. Therefore, we must pay attention to the debugging of modulation degree in debugging.
==========
Five, engineering examples
The Chengde County Broadcasting and Television Bureau of Hebei Province resumed the FM radio transmission in May 2009. At the same time as the FM radio broadcast was resumed, the FM sound column was installed in the main trunk roads and squares of the county, and the broadcasting of the county town was realized at a fixed time. The specific implementation method is as follows:
The predecessor of Chengde County People's Broadcasting Station was the Chengde County Broadcasting Station. On November 8, 1988, the station was officially established. Two broadcast transmission points were set up in the county towns of Nanshan and Daheishan, with a transmission frequency of 98.5 MHz. The county Nanshan signal mainly covers the surrounding areas of the county and the southern villages. The Daheishan signal mainly covers the middle and northern villages of the county, as well as some areas such as Chengde urban area, paddock, Fengning and Longhua.
In 1992, the Chengde County Broadcasting and Television Bureau began to build a cable TV network. In 1994, a cable television station was established. In 2002, radio stations were stopped due to various factors. In August 2007, the Chengde County Bureau set out to resume radio broadcast work, re-apply and get approved for use at frequencies of 91.3 MHz and 92.8 MHz. The official launch began on April 24, 2009, and the broadcast time is 15 hours and 30 minutes. The broadcast began at 6:30 in the morning and ended at 10 in the evening. In addition to broadcasting the news programs of the central, provincial and municipal radio stations, it also mainly runs the county's news programs, social news programs, information programs and audience hotline live programs. Make full use of the telephone platform, SMS platform and Internet platform to achieve interactive communication with the audience.
At the same time that the wireless FM radio signal was opened, Chengde County Radio and Television Bureau purchased 40 FM75-25W FM sound columns from Beijing Hengxing Ketong Technology Development Co., Ltd., and installed them in the main roads and squares of the county. Every day, in the morning, in the middle and in the evening, the FM sound column is turned on, and the broadcast signal covers the whole county, so that the long-lost broadcast sound returns to the people's side, greatly improving the cultural life level of the urban people, and is warmly welcomed and praised by the masses.
Chengde County People's Broadcasting Station will give full play to the advantages and characteristics of radio waves. It plans to use the wireless transmission method to install FM transmitters and tweeters in each administrative village of the county to realize the rural village "village ringing". The voice of the party and the government is transmitted to thousands of families. At the same time, we must gradually apply high-tech means, from a single audio media to multimedia, through multimedia to the TV, in the future will also be sent to the computer through the Internet, to achieve all-round publicity, to create mainstream, strong media in Chengde County, The county government and the people's government serve the people.
Sixth, the conclusion
The use of existing FM radio transmitters to implement addressable urban broadcasting and rural broadcasting is currently the best solution for achieving broadcast coverage. With wireless broadcasting, neither cumbersome wiring nor dedicated line maintenance is required, and point-to-point addressable broadcasting can be realized. In the event of an emergency, emergency evacuation, emergency command, etc. can be implemented and no secondary investment is required. The transmission of emergency broadcast signals can be realized on the basis of the original FM transmitter. Therefore, the extension based on existing FM transmitters is the preferred solution for rural broadcast coverage.
I. Introduction
With the promotion of China's "harmonious society construction" and radio and television "village-to-village" projects, after several decades of development of FM radio, basically every county has built FM radio stations to achieve coverage of broadcast signals in the region. But the number of radios owned by farmers is small, and the real broadcast signal to the home and the listening rate is very low. In the 1960s and 1970s, rural broadcasting had a good network foundation and management institutions. Basically, households had small speakers, and rural areas had “amplification stationsâ€. But then with the popularity of television, the broadcast gradually faded out of our horizons. Historically, broadcasting has a good mass base in rural areas, and even in today's society where information is highly developed, there is a great demand. At present, some places in China are gradually recovering rural broadcasting, as the assessment content of the new rural construction and the “village-to-village†project.
Under the current technical conditions, the method used to achieve the restoration of rural broadcasting is a problem faced by the government and the broadcasting and television authorities: whether to re-erect the barbed wire, or to use the existing cable TV network, telephone network, wireless FM network to achieve coverage of rural broadcasting? Let's take the SCA wireless FM broadcasting system of Beijing Hengxing Ketong Technology Development Co., Ltd. as an example to make a brief analysis on how to use the existing wireless FM broadcasting system to realize rural broadcasting.
Second, the introduction of frequency modulation subchannel (SCA) addressable technology
Wireless FM broadcasting is a method of adopting FM modulation of a broadcast signal, and modulating an audio signal onto an FM carrier of 87---108 MHz, converting a broadcast signal into a radio signal through an FM transmitter and a transmitting antenna, performing wireless transmission, and receiving A broadcast method that is listened to by an FM radio or a dedicated FM receiving device.
The SCA addressable control technology utilizes the SCA subchannel in the FM broadcast baseband (the 67KHz used as the subcarrier of the additional channel in China), and uses the FSK digital modulation method to implement the broadcast addressing function, that is, the addressing. The information is modulated by the frequency modulation method with a certain frequency offset (for the stereo broadcast, the maximum frequency offset of the modulation is 10% of the total frequency offset of the FM broadcast) to the primary carrier (ie, the FM broadcast frequency), and is transmitted along with the broadcast signal. The block diagram of the SCA addressable system control transmission part is shown in the figure below, and the reception is the inverse transform of the transmission.
figure 1
Third, the working principle of the system and the introduction of major equipment
1, the workflow: addressing information is through the computer serial port (RS-232) output digital signal, this digital stream is controlled by the intelligent broadcast master control software. The computer RS-232 serial port is connected with the HX-2500SCA digital encoder. The digital encoder uses the FSK digital modulation technology to modulate the signal to the 67KHz carrier. The 67KHz carrier is used as the FM broadcast subcarrier signal and is sent to the transmitter and audio. The signals are modulated together and amplified by the transmitter power amplifier and transmitted to space for propagation.
After receiving the RF carrier, the receiving end will automatically demodulate the SCA signal and the stereo audio signal. The audio signal is amplified to drive the speaker, and the SCA signal is sent to the decoding circuit and the relay to execute the switch command. Address function.
2. System composition: The system is mainly composed of HX-6000 main control software, HX-2500SCA subchannel encoder, FM70 FM sound column, FM4210 FM receiver controller, FM4310 FM receiver and other equipment, the following for each device The functions and technical parameters are described in detail.
==============
3. Introduction to major equipment
3.1, the system is mainly controlled by HX-6000
figure 2
HX-6000 digital multi-channel intelligent broadcasting system software is a new generation of intelligent broadcasting software independently developed by Beijing Hengxing Ketong Technology Development Co., Ltd. with independent intellectual property rights. Independently develop the playback engine, one computer can simultaneously output 1-6 channels of audio broadcast programs, and point-to-point addressing control. The software has obtained the "Computer Software Copyright Registration Certificate".
image 3
The software has terminal address and receive channel initialization, remote control terminal frequency and volume. Arbitrary partition grouping, addressing control function, multi-channel playback, emergency broadcast, external device timing switch, power timer switch, database backup and restore, automatic execution of playback tasks, automatic power on/off, etc. Play the software.
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系统硬件è¦æ±‚：586以上电脑，32M以上内å˜
æ“作系统è¦æ±‚：Windows95/98/2000/NT/XP或更高版本
=================
3.2ã€HX-2500SCA副信é“ç¼–ç 器
Figure 4
功能特点
HX-2500SCA副信é“æ•°å—ç¼–ç 器是智能调频系统的控制与数æ®ç¼–ç å˜æ¢ã€ä¼ 输的关键处ç†è®¾å¤‡ã€‚它利用频移键控（FSK）方å¼å°†æ•°å—é‡çš„控制信å·æ”¹å˜ä¸ºæ¨¡æ‹Ÿè½½æ³¢ï¼Œæ··å…¥è°ƒé¢‘广æ’çš„SCA副信é“ä¼ è¾“ï¼ŒæŽ§åˆ¶ä¿¡å·ä¸å•ç‹¬å 用频点，节约了频率资æºã€‚本编ç 调制器采用DDSæŠ€æœ¯è¿›è¡Œç›´æŽ¥è°ƒé¢‘ï¼Œå…·æœ‰é¢‘è°±å¹²å‡€ï¼Œé¢‘çŽ‡å‡†ç¡®æ— æ¼‚ç§»ï¼Œå 用带宽å°çš„特点，ä¿è¯äº†æŽ¥æ”¶ç«¯çš„低误ç ã€‚ä¼ è¾“é€šé“é€æ˜Žï¼Œå³å¯ç”¨ä¸Žæœ¬å…¬å¸çš„智能调频系统，也å¯å•ç‹¬ç”¨äºŽä¸ä½Žé€Ÿæ•°æ®ä¼ 输，主è¦ç‰¹ç‚¹å¦‚下：
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功能特点
FM75室外调频音柱是专业调频广æ’接收设备，集调频接收ã€åŠŸæ”¾ã€éŸ³ç®±ä¸ºä¸€ä½“的广æ’设备，采用é“åˆé‡‘一体化结构，外观美观大方，室外防雨设计，接收电路采用SMT贴片工艺，PHILIPS专业设备I2C。独特的SCA防æ’æ’è®¾è®¡ï¼Œåœ¨æ— è½½æ³¢å‘å°„ä¿¡å·æˆ–å—åˆ°æ— çº¿å¹²æ‰°æ—¶ï¼Œè‡ªåŠ¨å…³æœºã€‚æ”¯æŒHX-6000软件远程é¥æŽ§å¼€å…³æœºï¼Œè‡ªåŠ¨å®šç‚¹å®šæ—¶æ’音，最多å¯æ”¯æŒ2040个独立IDç¼–ç ，支æŒåœ¨çº¿åœ°å€ä¿®æ”¹ã€‚是农æ‘广æ’ã€æ™¯åŒºå¹¿æ’ã€æ ¡å›å¹¿æ’首选设备。å¯æ ¹æ®ç”¨æˆ·è¦æ±‚定制æˆè½½æ³¢æŽ§åˆ¶åž‹ã€SCA防æ’æ’型，点对点å¯å¯»å€åž‹ï¼Œä¹Ÿå¯å®šåˆ¶ä¸ºåŒç‚¹é¢‘优先切æ¢ã€‚
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频率用户指定82.5-108MHZ,å•ç‚¹é¢‘接收é¢å®šè¾“出功率10W/25W/35W/50W
频率长期稳定度15PPm 供电方å¼220V±20%/60V±10%
频率准确度-30°C～+60°C＜1KHz 功能åŠç»“æž„é“åˆé‡‘一体化结构é¢å®šè¾“入电平（FM）35±5dBu 外形尺寸40×200×350
3.4ã€FM4210调频接收控制器
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功能特点
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频率准确度1.5×10-6MHz 射频输入端å公制F头，75欧工作电平40-50dBµ 音频输出端åä¸å¹³è¡¡RCAå•å£°é“1组1.0V(å¯è°ƒ)
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=================================
3.5ã€FM4310多功能调频收扩机
功能特点
FM4310调频收扩机采用PLL微电脑控制频率åˆæˆé”相环技术，结åˆPHILIPS最新解调ICï¼Œå…·æœ‰é¢‘çŽ‡ç¨³å®šåº¦é«˜ï¼ŒéŸ³é¢‘æŒ‡æ ‡ä½³ã€æ“作方便ç‰ä¼˜ç‚¹ã€‚具有载波控制型和SCAæ•°å—ç¼–ç å¯å¯»å€åž‹ï¼Œæ”¯æŒè¿œç¨‹è½¯ä»¶å¼€å…³æœºç®¡ç†æŽ§åˆ¶ã€‚轻触å¼é¢æ¿æŽ§åˆ¶ï¼Œå…·æœ‰FMã€LINEã€MIC三ç§è¾“入选择，åŒå£°é“LED柱状电平动æ€æ˜¾ç¤ºï¼Œå¯ç”¨äºŽæ‘广æ’室调频广æ’ä¿¡å·æŽ¥æ”¶æ”¾å¤§ï¼Œç›´æŽ¥é©±åŠ¨é«˜éŸ³å–‡å。â—PLLé”相技术，82.5-108MHz全自动电调è°ã€æ‰‹åŠ¨è‡ªåŠ¨æœç´¢â—LEDæ•°å—频率，音é‡ã€ID地å€æ˜¾ç¤ºï¼ŒæŸ±çŠ¶ç”µå¹³åŠ¨æ€æ˜¾ç¤ºâ—轻触å¼é¢æ¿æŒ‰é”®å¼€å…³ï¼ŒLED状æ€æ˜¾ç¤ºï¼Œæ“作方便，人性化设计â—具有远程上级广æ’优先功能，远程é”定交互地æ“作â—定阻ã€å®šåŽ‹å¤šæ¨¡å¼è¾“出，适åˆåŒ¹é…定压定阻音箱å¼é«˜éŸ³å–‡å
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频率å“应50Hz-15KHz FM输入电平35dBμ-60dBμ/75欧姆射频输入端å公制F头,75欧线路输入47K/0dBm
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河北çœæ‰¿å¾·åŽ¿å¹¿æ’电视局于2009å¹´5月æ¢å¤äº†è°ƒé¢‘广æ’，在æ¢å¤è°ƒé¢‘广æ’çš„åŒæ—¶ï¼Œåœ¨åŽ¿åŸŽä¸»è¦å¹²é“ã€å¹¿åœºå®‰è£…了调频音柱，定点定时实现对县城的广æ’。具体实施方法如下：
承德县人民广æ’电å°çš„å‰èº«æ˜¯æ‰¿å¾·åŽ¿å¹¿æ’站，1988å¹´11月8æ—¥æ£å¼å»ºå°ï¼Œåœ¨åŽ¿åŸŽå—山和大黑山设立两个转æ’å‘射点，å‘射频率为98.5兆赫。县城å—山信å·ä¸»è¦è¦†ç›–县城周围åŠå—部乡æ‘，大黑山信å·ä¸»è¦è¦†ç›–全县ä¸åŒ—部乡æ‘，以åŠæ‰¿å¾·å¸‚区ã€å›´åœºã€ä¸°å®å’Œéš†åŒ–ç‰éƒ¨åˆ†åœ°åŒºã€‚
1992年，承德县广æ’电视局开始ç¹å»ºæœ‰çº¿ç”µè§†ç½‘络，1994å¹´æˆç«‹æœ‰çº¿ç”µè§†å°ï¼Œ2002å¹´ï¼Œå› å¤šç§å› ç´ çš„åˆ¶çº¦å¯¼è‡´å¹¿æ’电å°èŠ‚ç›®åœæ’。2007å¹´8月，承德县局ç€æ‰‹æ¢å¤ç”µå°æ’出工作，é‡æ–°ç”³è¯·å¹¶å¾—到批准使用频率为调频91.3兆赫和92.8兆赫。2009å¹´4月24日开始æ£å¼å¼€æ’，全天æ’出时间为15å°æ—¶30分钟。早上6点30分开始æ’音，晚上10点结æŸã€‚除转æ’ä¸å¤®ã€çœã€å¸‚广æ’电å°æ–°é—»èŠ‚目外，还主è¦å¼€åŠžæœ¬åŽ¿æ–°é—»èŠ‚ç›®ã€ç¤¾ä¼šæ–°é—»èŠ‚ç›®ã€èµ„讯节目和å¬ä¼—çƒçº¿ç›´æ’节目。充分利用电è¯å¹³å°ã€çŸä¿¡å¹³å°å’Œäº’è”网平å°ï¼Œä¸Žå¬ä¼—实现互动沟通。
æ¤æ¬¡åœ¨æ— 线调频广æ’ä¿¡å·å¼€é€šçš„åŒæ—¶ï¼Œæ‰¿å¾·åŽ¿å¹¿ç”µå±€å‘北京æ’星科通科技å‘展有é™å…¬å¸è´ä¹°äº†40åªFM75-25W调频音柱，安装在县城主è¦å¹²é“和广场。æ¯å¤©æ—©ã€ä¸ã€æ™šå®šæ—¶å¼€å¯è°ƒé¢‘音柱，广æ’ä¿¡å·è¦†ç›–全县，使久è¿çš„广æ’声音åˆå›žåˆ°ç™¾å§“的身边，大大æ高城区百姓的文化生活水平，å—到群众的çƒçƒˆæ¬¢è¿Žä¸Žå¥½è¯„。
承德县人民广æ’电å°å°†å……分å‘æŒ¥æ— çº¿ç”µæ³¢ä¼˜åŠ¿å’Œç‰¹ç‚¹ï¼Œè®¡åˆ’ä¸‹ä¸€æ¥é€šè¿‡æ— çº¿ä¼ è¾“æ–¹å¼ï¼Œè¦å°†å…¨åŽ¿æ¯ä¸ªè¡Œæ”¿æ‘都安装调频收扩机ã€é«˜éŸ³å–‡å，实现农æ‘广æ’“æ‘æ‘å“â€ï¼Œå°†å…šå’Œæ”¿åºœçš„å£°éŸ³ä¼ é€åˆ°åƒå®¶ä¸‡æˆ·ã€‚åŒæ—¶è¿˜è¦é€æ¥åº”用高科技手段，从å•ä¸€çš„音频媒体å‘多媒体é 拢，通过多媒体é€è¿›ç”µè§†æœºï¼Œå°†æ¥è¿˜è¦é€šè¿‡äº’è”网é€åˆ°è®¡ç®—机，实现全方ä½çš„å®£ä¼ ï¼Œæ‰“é€ æ‰¿å¾·åŽ¿çš„ä¸»æµã€å¼ºåŠ¿åª’体，为县委县政府和人民群众æœåŠ¡ã€‚
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利用现有调频广æ’å‘射机æ¥å®žçŽ°å¯å¯»å€åŸŽå¸‚广æ’ã€å†œæ‘广æ’，是当å‰å®žçŽ°å¹¿æ’覆盖的一ç§æœ€ä½³æ–¹æ¡ˆã€‚é‡‡ç”¨æ— çº¿å¹¿æ’，既ä¸éœ€è¦ç¹ç的布线，也ä¸éœ€è¦ä¸“门派人进行线路维护，åŒæ—¶å¯ä»¥å®žçŽ°ç‚¹å¯¹ç‚¹å¯å¯»å€å¹¿æ’。在å‘生紧急情况åŽï¼Œå¯ä»¥å®žçŽ°ç´§æ€¥ç–æ•£ã€ç´§æ€¥æŒ‡æŒ¥ç‰åŠŸèƒ½ï¼Œå¹¶ä¸”ä¸éœ€è¦äºŒæ¬¡æŠ•èµ„。在原有调频å‘射机的的基础上就å¯ä»¥å®žçŽ°ç´§æ€¥å¹¿æ’ä¿¡å·çš„ä¼ è¾“ã€‚æ‰€ä»¥ï¼Œåˆ©ç”¨çŽ°æœ‰è°ƒé¢‘å‘射机为基础进行扩展是农æ‘广æ’覆盖的首选方案。
With the promotion of China's "harmonious society construction" and radio and television "village-to-village" projects, after several decades of development of FM radio, basically every county has built FM radio stations to achieve coverage of broadcast signals in the region. But the number of radios owned by farmers is small, and the real broadcast signal to the home and the listening rate is very low. In the 1960s and 1970s, rural broadcasting had a good network foundation and management institutions. Basically, households had small speakers, and rural areas had “amplification stationsâ€. But then with the popularity of television, the broadcast gradually faded out of our horizons. Historically, broadcasting has a good mass base in rural areas, and even in today's society where information is highly developed, there is a great demand. At present, some places in China are gradually recovering rural broadcasting, as the assessment content of the new rural construction and the “village-to-village†project.
Under the current technical conditions, the method used to achieve the restoration of rural broadcasting is a problem faced by the government and the broadcasting and television authorities: whether to re-erect the barbed wire, or to use the existing cable TV network, telephone network, wireless FM network to achieve coverage of rural broadcasting? Let's take the SCA wireless FM broadcasting system of Beijing Hengxing Ketong Technology Development Co., Ltd. as an example to make a brief analysis on how to use the existing wireless FM broadcasting system to realize rural broadcasting.
Second, the introduction of frequency modulation subchannel (SCA) addressable technology
Wireless FM broadcasting is a method of adopting FM modulation of a broadcast signal, and modulating an audio signal onto an FM carrier of 87---108 MHz, converting a broadcast signal into a radio signal through an FM transmitter and a transmitting antenna, performing wireless transmission, and receiving A broadcast method that is listened to by an FM radio or a dedicated FM receiving device.
The SCA addressable control technology utilizes the SCA subchannel in the FM broadcast baseband (the 67KHz used as the subcarrier of the additional channel in China), and uses the FSK digital modulation method to implement the broadcast addressing function, that is, the addressing. The information is modulated by the frequency modulation method with a certain frequency offset (for the stereo broadcast, the maximum frequency offset of the modulation is 10% of the total frequency offset of the FM broadcast) to the primary carrier (ie, the FM broadcast frequency), and is transmitted along with the broadcast signal. The block diagram of the SCA addressable system control transmission part is shown in the figure below, and the reception is the inverse transform of the transmission.
figure 1
Third, the working principle of the system and the introduction of major equipment
1, the workflow: addressing information is through the computer serial port (RS-232) output digital signal, this digital stream is controlled by the intelligent broadcast master control software. The computer RS-232 serial port is connected with the HX-2500SCA digital encoder. The digital encoder uses the FSK digital modulation technology to modulate the signal to the 67KHz carrier. The 67KHz carrier is used as the FM broadcast subcarrier signal and is sent to the transmitter and audio. The signals are modulated together and amplified by the transmitter power amplifier and transmitted to space for propagation.
After receiving the RF carrier, the receiving end will automatically demodulate the SCA signal and the stereo audio signal. The audio signal is amplified to drive the speaker, and the SCA signal is sent to the decoding circuit and the relay to execute the switch command. Address function.
2. System composition: The system is mainly composed of HX-6000 main control software, HX-2500SCA subchannel encoder, FM70 FM sound column, FM4210 FM receiver controller, FM4310 FM receiver and other equipment, the following for each device The functions and technical parameters are described in detail.
==============
3. Introduction to major equipment
3.1, the system is mainly controlled by HX-6000
figure 2
HX-6000 digital multi-channel intelligent broadcasting system software is a new generation of intelligent broadcasting software independently developed by Beijing Hengxing Ketong Technology Development Co., Ltd. with independent intellectual property rights. Independently develop the playback engine, one computer can simultaneously output 1-6 channels of audio broadcast programs, and point-to-point addressing control. The software has obtained the "Computer Software Copyright Registration Certificate".
image 3
The software has terminal address and receive channel initialization, remote control terminal frequency and volume. Arbitrary partition grouping, addressing control function, multi-channel playback, emergency broadcast, external device timing switch, power timer switch, database backup and restore, automatic execution of playback tasks, automatic power on/off, etc. Play the software.
The software can be used for school language and teaching management activities such as foreign language teaching, music ringing, educational management, campus broadcasting, etc. It can also be applied to background music in rural radio, tourist attractions, industrial and mining enterprises, troops, institutions, communities and other places. Autoplay.
System hardware requirements: 586 or more computers, 32M or more memory
Operating system requirements: Windows95/98/2000/NT/XP or higher
=================
3.2, HX-2500SCA subchannel encoder
Figure 4
Features
The HX-2500SCA subchannel digital encoder is the key processing device for the control and data coding conversion and transmission of the intelligent frequency modulation system. It uses the frequency shift keying (FSK) method to change the digital control signal into an analog carrier, and mixes it into the SCA subchannel transmission of the FM broadcast. The control signal does not occupy the frequency point alone, which saves the frequency resources. The code modulator adopts DDS technology for direct frequency modulation, and has the characteristics of clean spectrum, accurate frequency without drift, occupying small bandwidth, and ensuring low error of the receiving end. The transmission channel is transparent and can be used with our intelligent FM system. It can also be used for medium and low speed data transmission. The main features are as follows:
ï¬ Support RS-485 and RS-232 control mode input;
ï¬ Data communication rate can reach 2400bit/s;
ï¬ Signal digital processing is strict, the waveform phase is accurate and error-free;
ï¬4th-order active filter to ensure no interference to the sound channel
ï¬ The signal transmission radius is basically equal to the broadcast coverage;
Technical indicators
Project technical parameter project technical parameter data modulation mode FSK carrier output amplitude 0-3VPP continuously adjustable carrier operating frequency 67K/70KHZ output impedance 600 ohm, Unbalanced
Carrier operating bandwidth PS working environment conditions -20 ~ +65 ° C
Out-of-band residual <45DB operating voltage AC220V/50Hz
Modulation data rate 2400bit power <5W
Data interface RS232, RS485 installation 1U cabinet
3.3, FM75 FM sound column
Features
FM75 outdoor FM sound column is a professional FM radio receiving equipment, which integrates FM receiving, power amplifier and speaker. It adopts aluminum alloy integrated structure, beautiful appearance, outdoor rainproof design, receiving circuit adopts SMT patch technology, PHILIPS Professional equipment I2C. The unique SCA anti-interpolation design automatically shuts down when there is no carrier transmission signal or wireless interference. Support HX-6000 software remote control switch machine, automatic fixed-point time broadcast, up to 2040 independent ID codes, support online address modification. It is the preferred equipment for rural broadcasting, scenic spot broadcasting, and campus broadcasting. It can be customized to carrier control type, SCA anti-interpolation type, point-to-point addressable type, or can be customized to double-point frequency priority switching.
â— Modular design, easy to repair â— PLL digital frequency synthesis, frequency accuracy, no frequency drift â— Addressable control or carrier automatic switch control â— Beautiful sound quality, volume can be adjusted separately â— Ultra low energy design, small standby current â—Outdoor waterproof and anti-corrosion design, suitable for light pole and wall suspension installation â— Suitable for wired closed circuit transmission, or can be customized for wireless reception
Figure 5
Project technical parameters project technical parameters model outdoor type FM75 squelch turn-on level 30dBu
Frequency user specified 82.5-108MHZ, single point frequency receiving rated output power 10W/25W/35W/50W
Frequency long-term stability 15PPm Power supply mode 220V±20%/60V±10%
Frequency accuracy -30°C～+60°C<1KHz Function and structure Aluminum alloy integrated structure Rated input level (FM) 35±5dBu Dimensions 40×200×350
3.4, FM4210 FM Receiver Controller
Figure 6
Features
The FM4210 FM receiving controller is a terminal control device for FM intelligent broadcasting system. It adopts microcomputer-controlled frequency synthesis phase-locked PLL technology and PHILIPS latest I2C. It has the advantages of high frequency stability, high audio index and convenient operation. It can demodulate FM signal into standard audio signal, and realize local CD, deck audio input, MIC local sound reinforcement, etc., and has a set of 220V AC controlled power output for managing external devices such as audio amplifiers. Switch on and off. It can be widely used in rural radio, campus FM radio, shopping malls, supermarkets and other FM signal demodulation, and can also be used for broadcast radio room monitoring.
â— Carrier level automatic switch machine or SCA remote addressable switch machine
â— Output power automatic control function for use by modulator or amplifier
â— Panel touch switch control with LED level display, volume display, etc.
â— FM, AUX, MIC panel selection switch, using professional audio switching chip
â— 82.5~108MHz full-band demodulation, audio frequency stepping 0.1MHz continuously adjustable
â— With SCA independent output, RS-232 interface for transmitting digital signals (such as LED screen)
â— SCA subcarrier control signal demodulation, accurate and stable, low bit error rate (SCA type has)
â—Using a 19-inch standard chassis, 2U height, aluminum brushed panel, beautiful appearance
â— Built-in 1W monitor speaker, monitor volume can be monotonous, convenient for local audio or radio monitor
Technical indicators
Technical parameters of the project Technical parameters Frequency range 82.5-108MHz, continuous adjustable selectivity 400KHz >60dB
Frequency accuracy 1.5×10-6MHz RF input terminal metric F head, 75 ohm working level 40-50dBμ Audio output terminal unbalanced RCA mono 1 set 1.0V (adjustable)
Signal to noise ratio 55dB power supply mode AC 220V ± 15%
Harmonic distortion (1KHz) 1% power control power ≤500W
Frequency response 80Hz-10KHz (±1.5dB) RS-232 output definition See the manual stereo separation 40dB monitor speaker power 1W
==================================
3.5, FM4310 multi-function frequency modulation and expansion machine
Features
FM4310 frequency modulation and expansion machine adopts PLL microcomputer to control frequency synthesis phase-locked loop technology, combined with PHILIPS latest demodulation IC, which has the advantages of high frequency stability, good audio index and convenient operation. It has carrier control type and SCA digital code addressable type, and supports remote software switch machine management control. Light touch panel control, with FM, LINE, MIC three input options, two-channel LED column level dynamic display, can be used for village broadcast room FM radio signal receiving amplification, direct drive tweeter. â— PLL phase-locking technology, 82.5-108MHz automatic electric tuning, manual automatic search â— LED digital frequency, volume, ID address display, column level dynamic display â— Light touch panel button switch, LED status display, easy to operate, user-friendly Design â— With remote superior broadcast priority function, remote lock interactive operation â— fixed resistance, constant pressure multi-mode output, suitable for matching constant pressure fixed-resistance speaker type tweeter
Technical indicators
Project technical parameters Project technical parameters Output impedance 4-16 ohms/70V/110V Constant voltage frequency range 82.5-108 MHz, frequency synthesis rated output power 50W/100W/150W (RMS, 8Ω) Frequency accuracy 1.5×10-6<1KHZ
Frequency response 50Hz-15KHz FM input level 35dBμ-60dBμ/75 ohm RF input terminal metric F head, 75 ohm line input 47K/0dBm
Power supply mode AC 220V ± 15% microphone input 600 ohms
Fourth, the technical points of installation and commissioning
At present, the FM transmitters (FM exciters) produced by FM transmitter manufacturers at home and abroad all have SCA subchannel interfaces (such as: RVR, Beiguang, Chengguang, Zhongchuan, Kaiteng Sifang, Tsinghua Yoshizhao, etc.). Under the existing radio transmitter, the SCA signal can be transmitted without any modification. The specific connection block diagram is as follows:
Figure 7
Key technology of installation and debugging: After the SCA signal is sent to the exciter, the modulation degree cannot be greater than 10% of the total frequency offset. If the SCA modulation is too large, it will interfere with the audio signal of the primary channel, resulting in degradation of the audio signal; if the SCA modulation is too small, the SCA decoding error rate will be high. Therefore, we must pay attention to the debugging of modulation degree in debugging.
==========
Five, engineering examples
The Chengde County Broadcasting and Television Bureau of Hebei Province resumed the FM radio transmission in May 2009. At the same time as the FM radio broadcast was resumed, the FM sound column was installed in the main trunk roads and squares of the county, and the broadcasting of the county town was realized at a fixed time. The specific implementation method is as follows:
The predecessor of Chengde County People's Broadcasting Station was the Chengde County Broadcasting Station. On November 8, 1988, the station was officially established. Two broadcast transmission points were set up in the county towns of Nanshan and Daheishan, with a transmission frequency of 98.5 MHz. The county Nanshan signal mainly covers the surrounding areas of the county and the southern villages. The Daheishan signal mainly covers the middle and northern villages of the county, as well as some areas such as Chengde urban area, paddock, Fengning and Longhua.
In 1992, the Chengde County Broadcasting and Television Bureau began to build a cable TV network. In 1994, a cable television station was established. In 2002, radio stations were stopped due to various factors. In August 2007, the Chengde County Bureau set out to resume radio broadcast work, re-apply and get approved for use at frequencies of 91.3 MHz and 92.8 MHz. The official launch began on April 24, 2009, and the broadcast time is 15 hours and 30 minutes. The broadcast began at 6:30 in the morning and ended at 10 in the evening. In addition to broadcasting the news programs of the central, provincial and municipal radio stations, it also mainly runs the county's news programs, social news programs, information programs and audience hotline live programs. Make full use of the telephone platform, SMS platform and Internet platform to achieve interactive communication with the audience.
At the same time that the wireless FM radio signal was opened, Chengde County Radio and Television Bureau purchased 40 FM75-25W FM sound columns from Beijing Hengxing Ketong Technology Development Co., Ltd., and installed them in the main roads and squares of the county. Every day, in the morning, in the middle and in the evening, the FM sound column is turned on, and the broadcast signal covers the whole county, so that the long-lost broadcast sound returns to the people's side, greatly improving the cultural life level of the urban people, and is warmly welcomed and praised by the masses.
Chengde County People's Broadcasting Station will give full play to the advantages and characteristics of radio waves. It plans to use the wireless transmission method to install FM transmitters and tweeters in each administrative village of the county to realize the rural village "village ringing". The voice of the party and the government is transmitted to thousands of families. At the same time, we must gradually apply high-tech means, from a single audio media to multimedia, through multimedia to the TV, in the future will also be sent to the computer through the Internet, to achieve all-round publicity, to create mainstream, strong media in Chengde County, The county government and the people's government serve the people.
Sixth, the conclusion
The use of existing FM radio transmitters to implement addressable urban broadcasting and rural broadcasting is currently the best solution for achieving broadcast coverage. With wireless broadcasting, neither cumbersome wiring nor dedicated line maintenance is required, and point-to-point addressable broadcasting can be realized. In the event of an emergency, emergency evacuation, emergency command, etc. can be implemented and no secondary investment is required. The transmission of emergency broadcast signals can be realized on the basis of the original FM transmitter. Therefore, the extension based on existing FM transmitters is the preferred solution for rural broadcast coverage.
I. Introduction
With the promotion of China's "harmonious society construction" and radio and television "village-to-village" projects, after several decades of development of FM radio, basically every county has built FM radio stations to achieve coverage of broadcast signals in the region. But the number of radios owned by farmers is small, and the real broadcast signal to the home and the listening rate is very low. In the 1960s and 1970s, rural broadcasting had a good network foundation and management institutions. Basically, households had small speakers, and rural areas had “amplification stationsâ€. But then with the popularity of television, the broadcast gradually faded out of our horizons. Historically, broadcasting has a good mass base in rural areas, and even in today's society where information is highly developed, there is a great demand. At present, some places in China are gradually recovering rural broadcasting, as the assessment content of the new rural construction and the “village-to-village†project.
Under the current technical conditions, the method used to achieve the restoration of rural broadcasting is a problem faced by the government and the broadcasting and television authorities: whether to re-erect the barbed wire, or to use the existing cable TV network, telephone network, wireless FM network to achieve coverage of rural broadcasting? Let's take the SCA wireless FM broadcasting system of Beijing Hengxing Ketong Technology Development Co., Ltd. as an example to make a brief analysis on how to use the existing wireless FM broadcasting system to realize rural broadcasting.
Second, the introduction of frequency modulation subchannel (SCA) addressable technology
Wireless FM broadcasting is a method of adopting FM modulation of a broadcast signal, and modulating an audio signal onto an FM carrier of 87---108 MHz, converting a broadcast signal into a radio signal through an FM transmitter and a transmitting antenna, performing wireless transmission, and receiving A broadcast method that is listened to by an FM radio or a dedicated FM receiving device.
The SCA addressable control technology utilizes the SCA subchannel in the FM broadcast baseband (the 67KHz used as the subcarrier of the additional channel in China), and uses the FSK digital modulation method to implement the broadcast addressing function, that is, the addressing. The information is modulated by the frequency modulation method with a certain frequency offset (for the stereo broadcast, the maximum frequency offset of the modulation is 10% of the total frequency offset of the FM broadcast) to the primary carrier (ie, the FM broadcast frequency), and is transmitted along with the broadcast signal. The block diagram of the SCA addressable system control transmission part is shown in the figure below, and the reception is the inverse transform of the transmission.
figure 1
Third, the working principle of the system and the introduction of major equipment
1, the workflow: addressing information is through the computer serial port (RS-232) output digital signal, this digital stream is controlled by the intelligent broadcast master control software. The computer RS-232 serial port is connected with the HX-2500SCA digital encoder. The digital encoder uses the FSK digital modulation technology to modulate the signal to the 67KHz carrier. The 67KHz carrier is used as the FM broadcast subcarrier signal and is sent to the transmitter and audio. The signals are modulated together and amplified by the transmitter power amplifier and transmitted to space for propagation.
After receiving the RF carrier, the receiving end will automatically demodulate the SCA signal and the stereo audio signal. The audio signal is amplified to drive the speaker, and the SCA signal is sent to the decoding circuit and the relay to execute the switch command. Address function.
2. System composition: The system is mainly composed of HX-6000 main control software, HX-2500SCA subchannel encoder, FM70 FM sound column, FM4210 FM receiver controller, FM4310 FM receiver and other equipment, the following for each device The functions and technical parameters are described in detail.
==============
3. Introduction to major equipment
3.1, the system is mainly controlled by HX-6000
figure 2
HX-6000 digital multi-channel intelligent broadcasting system software is a new generation of intelligent broadcasting software independently developed by Beijing Hengxing Ketong Technology Development Co., Ltd. with independent intellectual property rights. Independently develop the playback engine, one computer can simultaneously output 1-6 channels of audio broadcast programs, and point-to-point addressing control. The software has obtained the "Computer Software Copyright Registration Certificate".
image 3
The software has terminal address and receive channel initialization, remote control terminal frequency and volume. Arbitrary partition grouping, addressing control function, multi-channel playback, emergency broadcast, external device timing switch, power timer switch, database backup and restore, automatic execution of playback tasks, automatic power on/off, etc. Play the software.
The software can be used for school language and teaching management activities such as foreign language teaching, music ringing, educational management, campus broadcasting, etc. It can also be applied to background music in rural radio, tourist attractions, industrial and mining enterprises, troops, institutions, communities and other places. Autoplay.
System hardware requirements: 586 or more computers, 32M or more memory
Operating system requirements: Windows95/98/2000/NT/XP or higher
=================
3.2, HX-2500SCA subchannel encoder
Figure 4
Features
The HX-2500SCA subchannel digital encoder is the key processing device for the control and data coding conversion and transmission of the intelligent frequency modulation system. It uses the frequency shift keying (FSK) method to change the digital control signal into an analog carrier, and mixes it into the SCA subchannel transmission of the FM broadcast. The control signal does not occupy the frequency point alone, which saves the frequency resources. The code modulator adopts DDS technology for direct frequency modulation, and has the characteristics of clean spectrum, accurate frequency without drift, occupying small bandwidth, and ensuring low error of the receiving end. The transmission channel is transparent and can be used with our intelligent FM system. It can also be used for medium and low speed data transmission. The main features are as follows:
ï¬ Support RS-485 and RS-232 control mode input;
ï¬ Data communication rate can reach 2400bit/s;
ï¬ Signal digital processing is strict, the waveform phase is accurate and error-free;
ï¬ 4th-order active filter to ensure no interference to the sound channel
ï¬ The signal transmission radius is basically equal to the broadcast coverage;
Technical indicators
Project technical parameter project technical parameter data modulation mode FSK carrier output amplitude 0-3VPP continuously adjustable carrier operating frequency 67K/70KHZ output impedance 600 ohm, Unbalanced
Carrier operating bandwidth PS working environment conditions -20 ~ +65 ° C
Out-of-band residual <45DB operating voltage AC220V/50Hz
Modulation data rate 2400bit power <5W
Data interface RS232, RS485 installation 1U cabinet
3.3, FM75 FM sound column
Features
FM75 outdoor FM sound column is a professional FM radio receiving equipment, which integrates FM receiving, power amplifier and speaker. It adopts aluminum alloy integrated structure, beautiful appearance, outdoor rainproof design, receiving circuit adopts SMT patch technology, PHILIPS Professional equipment I2C. The unique SCA anti-interpolation design automatically shuts down when there is no carrier transmission signal or wireless interference. Support HX-6000 software remote control switch machine, automatic fixed-point time broadcast, up to 2040 independent ID codes, support online address modification. It is the preferred equipment for rural broadcasting, scenic spot broadcasting, and campus broadcasting. It can be customized to carrier control type, SCA anti-interpolation type, point-to-point addressable type, or can be customized to double-point frequency priority switching.
â— Modular design, easy to repair â— PLL digital frequency synthesis, frequency accuracy, no frequency drift â— Addressable control or carrier automatic switch control â— Beautiful sound quality, volume can be adjusted separately â— Ultra low energy design, small standby current â—Outdoor waterproof and anti-corrosion design, suitable for light pole and wall suspension installation â— Suitable for wired closed circuit transmission, or can be customized for wireless reception
Figure 5
Project technical parameters project technical parameters model outdoor type FM75 squelch turn-on level 30dBu
Frequency user specified 82.5-108MHZ, single point frequency receiving rated output power 10W/25W/35W/50W
Frequency long-term stability 15PPm Power supply mode 220V±20%/60V±10%
Frequency accuracy -30°C～+60°C<1KHz Function and structure Aluminum alloy integrated structure Rated input level (FM) 35±5dBu Dimensions 40×200×350
3.4, FM4210 FM Receiver Controller
Figure 6
Features
The FM4210 FM receiving controller is a terminal control device for FM intelligent broadcasting system. It adopts microcomputer-controlled frequency synthesis phase-locked PLL technology and PHILIPS latest I2C. It has the advantages of high frequency stability, high audio index and convenient operation. It can demodulate FM signal into standard audio signal, and realize local CD, deck audio input, MIC local sound reinforcement, etc., and has a set of 220V AC controlled power output for managing external devices such as audio amplifiers. Switch on and off. It can be widely used in rural radio, campus FM radio, shopping malls, supermarkets and other FM signal demodulation, and can also be used for broadcast radio room monitoring.
â— Carrier level automatic switch machine or SCA remote addressable switch machine
â— Output power automatic control function for use by modulator or amplifier
â— Panel touch switch control with LED level display, volume display, etc.
â— FM, AUX, MIC panel selection switch, using professional audio switching chip
â— 82.5~108MHz full-band demodulation, audio frequency stepping 0.1MHz continuously adjustable
â— With SCA independent output, RS-232 interface for transmitting digital signals (such as LED screen)
â— SCA subcarrier control signal demodulation, accurate and stable, low bit error rate (SCA type has)
â—Using a 19-inch standard chassis, 2U height, aluminum brushed panel, beautiful appearance
â— Built-in 1W monitor speaker, monitor volume can be monotonous, convenient for local audio or radio monitor
Technical indicators
Technical parameters of the project Technical parameters Frequency range 82.5-108MHz, continuous adjustable selectivity 400KHz >60dB
Frequency accuracy 1.5×10-6MHz RF input terminal metric F head, 75 ohm working level 40-50dBμ Audio output terminal unbalanced RCA mono 1 set 1.0V (adjustable)
Signal to noise ratio 55dB power supply mode AC 220V ± 15%
Harmonic distortion (1KHz) 1% power control power ≤500W
Frequency response 80Hz-10KHz (±1.5dB) RS-232 output definition See the manual stereo separation 40dB monitor speaker power 1W
==================================
3.5, FM4310 multi-function frequency modulation and expansion machine
Features
FM4310 frequency modulation and expansion machine adopts PLL microcomputer to control frequency synthesis phase-locked loop technology, combined with PHILIPS latest demodulation IC, which has the advantages of high frequency stability, good audio index and convenient operation. It has carrier control type and SCA digital code addressable type, and supports remote software switch machine management control. Light touch panel control, with FM, LINE, MIC three input options, two-channel LED column level dynamic display, can be used for village broadcast room FM radio signal receiving amplification, direct drive tweeter. â— PLL phase-locking technology, 82.5-108MHz automatic electric tuning, manual automatic search â— LED digital frequency, volume, ID address display, column level dynamic display â— Light touch panel button switch, LED status display, easy to operate, user-friendly Design â— With remote superior broadcast priority function, remote lock interactive operation â— fixed resistance, constant pressure multi-mode output, suitable for matching constant pressure fixed-resistance speaker type tweeter
Technical indicators
Project technical parameters Project technical parameters Output impedance 4-16 ohms/70V/110V Constant voltage frequency range 82.5-108 MHz, frequency synthesis rated output power 50W/100W/150W (RMS, 8Ω) Frequency accuracy 1.5×10-6<1KHZ
Frequency response 50Hz-15KHz FM input level 35dBμ-60dBμ/75 ohm RF input terminal metric F head, 75 ohm line input 47K/0dBm
Power supply mode AC 220V ± 15% microphone input 600 ohms
Fourth, the technical points of installation and commissioning
At present, the FM transmitters (FM exciters) produced by FM transmitter manufacturers at home and abroad all have SCA subchannel interfaces (such as: RVR, Beiguang, Chengguang, Zhongchuan, Kaiteng Sifang, Tsinghua Yoshizhao, etc.). Under the existing radio transmitter, the SCA signal can be transmitted without any modification. The specific connection block diagram is as follows:
Figure 7
Key technology of installation and debugging: After the SCA signal is sent to the exciter, the modulation degree cannot be greater than 10% of the total frequency offset. If the SCA modulation is too large, it will interfere with the audio signal of the primary channel, resulting in degradation of the audio signal; if the SCA modulation is too small, the SCA decoding error rate will be high. Therefore, we must pay attention to the debugging of modulation degree in debugging.
==========
Five, engineering examples
The Chengde County Broadcasting and Television Bureau of Hebei Province resumed the FM radio transmission in May 2009. At the same time as the FM radio broadcast was resumed, the FM sound column was installed in the main trunk roads and squares of the county, and the broadcasting of the county town was realized at a fixed time. The specific implementation method is as follows:
The predecessor of Chengde County People's Broadcasting Station was the Chengde County Broadcasting Station. On November 8, 1988, the station was officially established. Two broadcast transmission points were set up in the county towns of Nanshan and Daheishan, with a transmission frequency of 98.5 MHz. The county Nanshan signal mainly covers the surrounding areas of the county and the southern villages. The Daheishan signal mainly covers the middle and northern villages of the county, as well as some areas such as Chengde urban area, paddock, Fengning and Longhua.
In 1992, the Chengde County Broadcasting and Television Bureau began to build a cable TV network. In 1994, a cable television station was established. In 2002, radio stations were stopped due to various factors. In August 2007, the Chengde County Bureau set out to resume radio broadcast work, re-apply and get approved for use at frequencies of 91.3 MHz and 92.8 MHz. The official launch began on April 24, 2009, and the broadcast time is 15 hours and 30 minutes. The broadcast began at 6:30 in the morning and ended at 10 in the evening. In addition to broadcasting the news programs of the central, provincial and municipal radio stations, it also mainly runs the county's news programs, social news programs, information programs and audience hotline live programs. Make full use of the telephone platform, SMS platform and Internet platform to achieve interactive communication with the audience.
At the same time that the wireless FM radio signal was opened, Chengde County Radio and Television Bureau purchased 40 FM75-25W FM sound columns from Beijing Hengxing Ketong Technology Development Co., Ltd., and installed them in the main roads and squares of the county. Every day, in the morning, in the middle and in the evening, the FM sound column is turned on, and the broadcast signal covers the whole county, so that the long-lost broadcast sound returns to the people's side, greatly improving the cultural life level of the urban people, and is warmly welcomed and praised by the masses.
Chengde County People's Broadcasting Station will give full play to the advantages and characteristics of radio waves. It plans to use the wireless transmission method to install FM transmitters and tweeters in each administrative village of the county to realize the rural village "village ringing". The voice of the party and the government is transmitted to thousands of families. At the same time, we must gradually apply high-tech means, from a single audio media to multimedia, through multimedia to the TV, in the future will also be sent to the computer through the Internet, to achieve all-round publicity, to create mainstream, strong media in Chengde County, The county government and the people's government serve the people.
Sixth, the conclusion
The use of existing FM radio transmitters to implement addressable urban broadcasting and rural broadcasting is currently the best solution for achieving broadcast coverage. With wireless broadcasting, neither cumbersome wiring nor dedicated line maintenance is required, and point-to-point addressable broadcasting can be realized. In the event of an emergency, emergency evacuation, emergency command, etc. can be implemented and no secondary investment is required. The transmission of emergency broadcast signals can be realized on the basis of the original FM transmitter. Therefore, the extension based on existing FM transmitters is the preferred solution for rural broadcast coverage.
I. Introduction
With the promotion of China's "harmonious society construction" and radio and television "village-to-village" projects, after several decades of development of FM radio, basically every county has built FM radio stations to achieve coverage of broadcast signals in the region. But the number of radios owned by farmers is small, and the real broadcast signal to the home and the listening rate is very low. In the 1960s and 1970s, rural broadcasting had a good network foundation and management institutions. Basically, households had small speakers, and rural areas had “amplification stationsâ€. But then with the popularity of television, the broadcast gradually faded out of our horizons. Historically, broadcasting has a good mass base in rural areas, and even in today's society where information is highly developed, there is a great demand. At present, some places in China are gradually recovering rural broadcasting, as the assessment content of the new rural construction and the “village-to-village†project.
Under the current technical conditions, the method used to achieve the restoration of rural broadcasting is a problem faced by the government and the broadcasting and television authorities: whether to re-erect the barbed wire, or to use the existing cable TV network, telephone network, wireless FM network to achieve coverage of rural broadcasting? Let's take the SCA wireless FM broadcasting system of Beijing Hengxing Ketong Technology Development Co., Ltd. as an example to make a brief analysis on how to use the existing wireless FM broadcasting system to realize rural broadcasting.
Second, the introduction of frequency modulation subchannel (SCA) addressable technology
Wireless FM broadcasting is a method of adopting FM modulation of a broadcast signal, and modulating an audio signal onto an FM carrier of 87---108 MHz, converting a broadcast signal into a radio signal through an FM transmitter and a transmitting antenna, performing wireless transmission, and receiving A broadcast method that is listened to by an FM radio or a dedicated FM receiving device.
The SCA addressable control technology utilizes the SCA subchannel in the FM broadcast baseband (the 67KHz used as the subcarrier of the additional channel in China), and uses the FSK digital modulation method to implement the broadcast addressing function, that is, the addressing. The information is modulated by the frequency modulation method with a certain frequency offset (for the stereo broadcast, the maximum frequency offset of the modulation is 10% of the total frequency offset of the FM broadcast) to the primary carrier (ie, the FM broadcast frequency), and is transmitted along with the broadcast signal. The block diagram of the SCA addressable system control transmission part is shown in the figure below, and the reception is the inverse transform of the transmission.
figure 1
Third, the working principle of the system and the introduction of major equipment
1, the workflow: addressing information is through the computer serial port (RS-232) output digital signal, this digital stream is controlled by the intelligent broadcast master control software. The computer RS-232 serial port is connected with the HX-2500SCA digital encoder. The digital encoder uses the FSK digital modulation technology to modulate the signal to the 67KHz carrier. The 67KHz carrier is used as the FM broadcast subcarrier signal and is sent to the transmitter and audio. The signals are modulated together and amplified by the transmitter power amplifier and transmitted to space for propagation.
After receiving the RF carrier, the receiving end will automatically demodulate the SCA signal and the stereo audio signal. The audio signal is amplified to drive the speaker, and the SCA signal is sent to the decoding circuit and the relay to execute the switch command. Address function.
2. System composition: The system is mainly composed of HX-6000 main control software, HX-2500SCA subchannel encoder, FM70 FM sound column, FM4210 FM receiver controller, FM4310 FM receiver and other equipment, the following for each device The functions and technical parameters are described in detail.
==============
3. Introduction to major equipment
3.1, the system is mainly controlled by HX-6000
figure 2
HX-6000 digital multi-channel intelligent broadcasting system software is a new generation of intelligent broadcasting software independently developed by Beijing Hengxing Ketong Technology Development Co., Ltd. with independent intellectual property rights. Independently develop the playback engine, one computer can simultaneously output 1-6 channels of audio broadcast programs, and point-to-point addressing control. The software has obtained the "Computer Software Copyright Registration Certificate".
image 3
The software has terminal address and receive channel initialization, remote control terminal frequency and volume. Arbitrary partition grouping, addressing control function, multi-channel playback, emergency broadcast, external device timing switch, power timer switch, database backup and restore, automatic execution of playback tasks, automatic power on/off, etc. Play the software.
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系统硬件è¦æ±‚：586以上电脑，32M以上内å˜
æ“作系统è¦æ±‚：Windows95/98/2000/NT/XP或更高版本
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3.2ã€HX-2500SCA副信é“ç¼–ç 器
Figure 4
功能特点
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3.4ã€FM4210调频接收控制器
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功能特点
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3.5ã€FM4310多功能调频收扩机
功能特点
FM4310调频收扩机采用PLL微电脑控制频率åˆæˆé”相环技术，结åˆPHILIPS最新解调ICï¼Œå…·æœ‰é¢‘çŽ‡ç¨³å®šåº¦é«˜ï¼ŒéŸ³é¢‘æŒ‡æ ‡ä½³ã€æ“作方便ç‰ä¼˜ç‚¹ã€‚具有载波控制型和SCAæ•°å—ç¼–ç å¯å¯»å€åž‹ï¼Œæ”¯æŒè¿œç¨‹è½¯ä»¶å¼€å…³æœºç®¡ç†æŽ§åˆ¶ã€‚轻触å¼é¢æ¿æŽ§åˆ¶ï¼Œå…·æœ‰FMã€LINEã€MIC三ç§è¾“入选择，åŒå£°é“LED柱状电平动æ€æ˜¾ç¤ºï¼Œå¯ç”¨äºŽæ‘广æ’室调频广æ’ä¿¡å·æŽ¥æ”¶æ”¾å¤§ï¼Œç›´æŽ¥é©±åŠ¨é«˜éŸ³å–‡å。â—PLLé”相技术，82.5-108MHz全自动电调è°ã€æ‰‹åŠ¨è‡ªåŠ¨æœç´¢â—LEDæ•°å—频率，音é‡ã€ID地å€æ˜¾ç¤ºï¼ŒæŸ±çŠ¶ç”µå¹³åŠ¨æ€æ˜¾ç¤ºâ—轻触å¼é¢æ¿æŒ‰é”®å¼€å…³ï¼ŒLED状æ€æ˜¾ç¤ºï¼Œæ“作方便，人性化设计â—具有远程上级广æ’优先功能，远程é”定交互地æ“作â—定阻ã€å®šåŽ‹å¤šæ¨¡å¼è¾“出，适åˆåŒ¹é…定压定阻音箱å¼é«˜éŸ³å–‡å
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