Frequently Asked Questions of Digital Wireless Addressable Intelligent FM Broadcast System
1. For school construction broadcasting, which frequency band is better for transmitting broadcasting signals? why?
Answer: It is better to use 70-87MHz FM carrier to transmit broadcast signals.
Because 88-108MHz is a public broadcast frequency band, most open-circuit wireless radio stations use this frequency band for transmission, during which the wireless resources are more complicated and more harmonics. If this frequency band is used to transmit campus broadcast signals, it is susceptible to interference and even speaker self-sound This phenomenon is not suitable for the practical needs of campus broadcasting to maintain the stability and reliability of daily teaching order.
The 70-87MHz frequency band is relatively clean and there are few wireless broadcast signals. It is used to transmit campus broadcast signals stably and reliably.
2. I heard that wireless broadcast is prone to frequency drift in both transmission and reception, resulting in signal instability and control failure. Is there such a phenomenon? what is the reason?
Answer: Yes, because some manufacturers are blindly pursuing low-priced products and are reluctant to make some technological changes, this phenomenon has indeed happened, and we have transformed several such projects.
As I mentioned in the last question, stability and reliability are the primary considerations for building a campus broadcasting system. An unstable time does not ring when it sounds, it does not control when it controls, or it does not sound when it makes a sound When the sound is not loud, the screaming campus radio can not meet the requirements of daily maintenance of teaching order, so the school should carefully investigate and choose carefully when choosing the campus radio products. Do not blindly pursue low prices, causing inconvenience in use.
Causes of frequency instability and control failure: the electrical curve characteristics of the components of the transmitting and receiving equipment are changed by temperature changes, resulting in unstable frequency phase and amplitude; the selected frequency is affected by the frequency of other radio wave signals; the selected control transmission channel is affected by harmonics The interference is serious, or the bit error rate is high.
3. How does Beijing Hengxing Ketong's products prevent the above phenomenon?
Answer: The launching of the above phenomenon is technically started from the following five aspects:
1) FM carrier transmission: The internationally advanced PLL microcomputer phase-locked loop technology is used to lock the transmission FM carrier, so that the transmitting device will not drift due to temperature changes and cause unstable frequency transmission.
2) Double-layer cross antenna: high-gain vertical polarized wave transmitting antenna is selected to ensure that the transmitted signal is stable and reliable and will not be affected by weather changes.
3) FM speaker sound column: The crystal oscillation frequency is used. The crystal is made of quartz. Quartz has the characteristics of low melting point and insignificant change under normal temperature, so that the reception frequency is stable at a certain point and the frequency will not drift.
4) Determination of frequency selection: use the 70-87MHz frequency band with less wireless frequency, select the clean frequency point, and transmit the campus broadcast signal at a frequency without any signal and harmonic interference to ensure the stability and reliability of campus broadcast.
5) Unique SCA control: the use of internationally advanced SCA subcarrier transmission control signal, with simple implementation, low bit error rate, saving resources (referring to frequency resources) and other characteristics, is the preferred transmission method for wireless transmission of control signals.
4. Does wireless broadcasting emphasize power wattage matching? What about scalability?
Answer: Wireless broadcasting only needs to meet terminal standards for a certain level of reception. It is different from the combination of fixed-voltage broadcasting amplifiers and speakers, and does not pay attention to the matching of power wattage.
As long as wireless broadcasting can be expanded on the basis of satisfying the level, in principle, our broadcasting software supports 1024 partitions, and supports multiple points and one zone, which is more than enough for the construction of campus broadcasting systems.
5. Why does Beijing Hengxing recommend schools to use high-power transmitters for wireless broadcasting?
Answer: Going back to the original question, considering the need for stability and reliability of campus broadcasting construction, we have increased the threshold level of the terminal receiving equipment to prevent the receiving equipment from being interfered by other weak signals.
For wireless FM earphones or radios, you can listen to wireless radio programs when the level reaches about 25dB. If there is severe harmonic interference near the selected frequency, you will hear whine or squeaking noise, and even strings Taiwan phenomenon.
After carefully studying and analyzing the needs of campus broadcasting and considering the development status and direction of wireless broadcasting in China, we decided to increase the level of terminal receiving equipment to about 40dB to improve the anti-interference performance of the entire system and ensure that the system can be stable for a long time. run.
Then, obviously, the level index of the terminal receiving equipment is improved, and the power of the transmitting equipment should be adjusted and increased accordingly. Through the adjustment of transmitter power and terminal reception level, we have greatly improved and strengthened the stability of the system, ensured that customers can use the product with confidence, and eliminated serious effects such as insensitive control, unstable audio signals, and wireless harmonics. The phenomenon of using effect occurs.
1. For school construction broadcasting, which frequency band is better for transmitting broadcasting signals? why?
Answer: It is better to use 70-87MHz FM carrier to transmit broadcast signals.
Because 88-108MHz is a public broadcast frequency band, most open-circuit wireless radio stations use this frequency band for transmission, during which the wireless resources are more complicated and more harmonics. If this frequency band is used to transmit campus broadcast signals, it is susceptible to interference and even speaker self-sound This phenomenon is not suitable for the practical needs of campus broadcasting to maintain the stability and reliability of daily teaching order.
The 70-87MHz frequency band is relatively clean and there are few wireless broadcast signals. It is used to transmit campus broadcast signals stably and reliably.
2. I heard that wireless broadcast is prone to frequency drift in both transmission and reception, resulting in signal instability and control failure. Is there such a phenomenon? what is the reason?
Answer: Yes, because some manufacturers are blindly pursuing low-priced products and are reluctant to make some technological changes, this phenomenon has indeed happened, and we have transformed several such projects.
As I mentioned in the last question, stability and reliability are the primary considerations for building a campus broadcasting system. An unstable time does not ring when it sounds, it does not control when it controls, or it does not sound when it makes a sound When the sound is not loud, the screaming campus radio can not meet the requirements of daily maintenance of teaching order, so the school should carefully investigate and choose carefully when choosing the campus radio products. Do not blindly pursue low prices, causing inconvenience in use.
Causes of frequency instability and control failure: the electrical curve characteristics of the components of the transmitting and receiving equipment are changed by temperature changes, resulting in unstable frequency phase and amplitude; the selected frequency is affected by the frequency of other radio wave signals; the selected control transmission channel is affected by harmonics The interference is serious, or the bit error rate is high.
3. How does Beijing Hengxing Ketong's products prevent the above phenomenon?
Answer: The launching of the above phenomenon is technically started from the following five aspects:
1) FM carrier transmission: The internationally advanced PLL microcomputer phase-locked loop technology is used to lock the transmission FM carrier, so that the transmitting device will not drift due to temperature changes and cause unstable frequency transmission.
2) Double-layer cross antenna: high-gain vertical polarized wave transmitting antenna is selected to ensure that the transmitted signal is stable and reliable and will not be affected by weather changes.
3) FM speaker sound column: The crystal oscillation frequency is used. The crystal is made of quartz. Quartz has the characteristics of low melting point and insignificant change under normal temperature, so that the reception frequency is stable at a certain point and the frequency will not drift.
4) Determination of frequency selection: use the 70-87MHz frequency band with less wireless frequency, select the clean frequency point, and transmit the campus broadcast signal at a frequency without any signal and harmonic interference to ensure the stability and reliability of campus broadcast.
5) Unique SCA control: the use of internationally advanced SCA subcarrier transmission control signal, with simple implementation, low bit error rate, saving resources (referring to frequency resources) and other characteristics, is the preferred transmission method for wireless transmission of control signals.
4. Does wireless broadcasting emphasize power wattage matching? What about scalability?
Answer: Wireless broadcasting only needs to meet terminal standards for a certain level of reception. It is different from the combination of fixed-voltage broadcasting amplifiers and speakers, and does not pay attention to the matching of power wattage.
As long as wireless broadcasting can be expanded on the basis of satisfying the level, in principle, our broadcasting software supports 1024 partitions, and supports multiple points and one zone, which is more than enough for the construction of campus broadcasting systems.
5. Why does Beijing Hengxing recommend schools to use high-power transmitters for wireless broadcasting?
Answer: Going back to the original question, considering the need for stability and reliability of campus broadcasting construction, we have increased the threshold level of the terminal receiving equipment to prevent the receiving equipment from being interfered by other weak signals.
For wireless FM earphones or radios, you can listen to wireless radio programs when the level reaches about 25dB. If there is severe harmonic interference near the selected frequency, you will hear whine or squeaking noise, and even strings Taiwan phenomenon.
After carefully studying and analyzing the needs of campus broadcasting and considering the development status and direction of wireless broadcasting in China, we decided to increase the level of terminal receiving equipment to about 40dB to improve the anti-interference performance of the entire system and ensure that the system can be stable for a long time. run.
Then, obviously, the level index of the terminal receiving equipment is improved, and the power of the transmitting equipment should be adjusted and increased accordingly. Through the adjustment of transmitter power and terminal reception level, we have greatly improved and strengthened the stability of the system, ensured that customers can use the product with confidence, and eliminated serious effects such as insensitive control, unstable audio signals, and wireless harmonics. The phenomenon of using effect occurs.
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