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What’s the advantage of Digital FM Transmitter?

数字调频发射机与模拟调频广播发射机相比具有如下突出的技术优势:

Digital FM Transmitter has the following outstanding technical advantages compare to the Analog FM Transmitter:

1、改善了音质:由于采用全过程的数字化处理,调频广播的音质可达到接近CD的水平;

1. Improve the quality of sound: it uses Digital Signal Process (DSP) technology, the sound quality is like CD.

2、提高了发射机可靠性:由于采用大规模集成电路作为主要元件(原件数量少,集成电路自身的可靠性极高),取代了模拟调频发射机的大量分立元件和小规模集成电路,是整机可靠性极大地提高;

2. Improve the reliability of transmitter: it uses large-scale integration circuit as main components. (Less components parts and high reliability of LSI), it’s instead of multiple discrete parts in Analog FM Transmitter, the quality and reliability has greatly improved.

3、发射机的功能柔性大:由于采用了软件无线电技术,所以在保持发射机硬件不变得情况下、只要装入不同的软件就可以生产出不同功能的调频发射机,这特别有利于厂家生产组织、也有利于发射机的升级改造;

3. The function is flexible of FM Transmitter: it uses wireless radio software technology, so factory can produce different function of FM Transmitters with the same Hardware. It’s very convenient for production and upgrade

4、可实现准确的远程监控和故障诊断:由于所有原来由硬件实现的功能都已软件化,所以不仅在发射机的LCD显示屏上可以观察到许多模拟发射机不可能观察的内部状态,而且可将这些状态通过通讯接口(RS232/RS485/CAN/TCPIP)在远程进行监控和故障诊断。

4. It can realize accurate remote control; monitoring and fault diagnosis: because of all Hardware function change into Software, so the Transmitter LCD screen can display many status parameters which can not display in Analog Transmitter. Also these status parameters can be monitored by (RS232/RS485/CAN/TCPIP) Remote control system.

5、可实现双路音频输入自动切换功能:在某些对系统可靠性要求较高的场合,可将数字音频和模拟音频同时输入到数字调频发射机,在其内部可实现以数字音频输入为主的自动音频切换功能,可省去外部的音频应急切换器。

5. It can realize Automatic Switch of Double-Audio signal input: It can input both Analog & Digital Audio Signal to the Digital FM Transmitter when radio station needs high reliability environment. It no needs external audio switcher, because it has internal automatic audio switcher for digital audio input signal.

  

What’s the working principle of digital FM radio transmitter?

Digital FM Transmitter has essential difference from Analog FM Transmitter.

For short, Analog FM Transmitter uses VCO+PLL analog technology, but Digital FM Transmitter uses DSP+DDS software wireless radio digital technology, the diagram as below:





 

Working Principle:

The Digital FM Transmitter includes 6 module parts: Audio Signal Input module; Digital Signal Process module; Digital FM Modulator and Band Pass Filter module; Output power amplifier and low-pass filter module; Man-machine Interface & Communication module and Power Supply & Circuit module.

Audio Signal Input module: It receive audio input signal and digital audio (AES/EBU) input signal. Analog audio signal convert into digital audio through (A/D) converter, then input DSP. Digital audio input DSP directly. The DSP will choose which signal can be the input audio signal.

Digital Signal Process module: This is the Key part in Exciter/Transmitter, the core is high performance 550MHz digital signal processor (DSP), this DSP can be controlled by software and process digital audio signal for gain adjustment; digital filtering; digital pre-emphasis; digital pilot occurs; digital stereo coding, and then create stereo composite signal flow, after mathematical operation, the flow will be modulated to the FM exciter baseband flow, it will be digital FM flow signal, this flow signal will be sent to 1000MHz Direct Digital Synthesizer (DDS), then change into FM RF Signal.

Digital FM Modulator and Band Pass Filter module: The core of this unit is Direct Digital Synthesizer (DDS), it receive digital FM flow signal from DSP, and then synthesize to the digital FM RF signal through its internal direct frequency synthesizer, its internal digital/analog converter can create analog FM modulated signal, finally get pure FM RF signal from Band-pass Filter.

Output power amplifier and low-pass filter module: This unit is closed loop Automatic Gain Control (AGC) FM RF power amplifier and low-pass filter circuit. It can ensure the setting output power is stable in long working period.

Man-machine Interface & Communication module: This unit uses one high performance System-on-a-Chip (SOC) to process Exciter/Transmitter Man-machine Interface; Operational data collection; Alarm protection; Communication and other functions. All operation order is input by button; LCD screen and light display Transmitter Status. It can use RS232/RS485/CAN/TCPIP communication interface connect with remote PC for data transmission and remote control function.

Power Supply & Circuit module: it supply DC stable voltage power for each function units in Transmitter.



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