How to distinguish the digital FM transmitter and the analog FM transmitter?

How to distinguish the digital FM transmitter and the analog FM transmitter?
     At present, many broadcast transmitter field technicians are wondering: many transmitter manufacturers claim that their own production of the FM transmitter is a digital FM transmitter, but in the end should be how to identify a FM transmitter is a digital FM transmitter? Issued the following advice for colleagues to identify reference.
    Identify an FM radio transmitter is the digitization of the most effective way is to look at the circuit schematic, the current FM transmitter FM transmitter circuit schematic of the following three forms:
    1, analog FM transmitter: You can only receive analog audio signal, audio signal amplification, analog limiter and stereo encoder; using the VCO (voltage controlled oscillator) + PLL (Phase Locked Loop) to produce the FM carrier frequency signal the process of course modulated analog composite audio signal direct modulation of the VCO varactor. This circuit is a typical analog FM transmitter, but there may be LED or LCD digital display to the operating frequency of the transmitter, but the whole process of simulation.
   This model is referred to as "VCO + PLL.

    2, a digital FM transmitter: can receive digital audio signals (AES / EBU) or analog audio signal, audio signal processing, stereo encoded by the DSP (digital signal processor) to complete the composite stereo signal by the D / A converter conversion analog stereo composite signal, the FM modulation signal of the VCO. Thus, before you generate a stereo composite signal is digitized, and then is no different from the analog FM transmitter.
   Referred to as "DSP + PLL.

    3 Digital FM Transmitter: the digitized audio to the whole process of the RF FM broadcast transmitters. It receives digital audio signals (AES / EBU) or analog audio signal (into the A / D), audio signal processing, stereo encoded by the DSP (digital signal processor) to complete, while the FM modulation process DSP to control the DDS (Direct Digital frequency synthesizer) to complete the digital modulation process. Discrete digital FM wave conventional FM wave produced by the D / A converter for RF amplifier to the specified power. Referred to as "of DSP + DDS.

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