At present, many FM launch field of technical personnel are very puzzled: many manufacturers of transmitters are claiming that their production of FM transmitter is a digital FM transmitter, but in the end should be how to identify an FM transmitter is the digital FM transmitter? The following comments are made here for your colleagues ' reference.
The most effective way to identify whether an FM radio transmitter is digital is to see its circuit principle, the current FM transmitter in the market has the following three kinds of circuit Principle FM Transmitter:
1, Analog FM Transmitter: can only receive analog audio signals, audio signal amplification, limit and stereo coding are analog, especially the use of VCO (voltage control oscillator) +PLL (phase-locked loop) to generate FM carrier signal, modulation of course is also the use of analog composite audio signal to the VCO variable capacitance diode direct modulation. This circuit is a typical analog FM transmitter, but may have led or LCD digital display transmitter operating frequency, but the whole process is simulated.
This mode is referred to as "VCO+PLL".
2, half-digital FM Transmitter: Can receive digital audio signal (AES/EBU) or analog audio signal, audio signal processing, stereo coding by DSP (digital signal processor) to complete, stereo composite signal through D/a converter to simulate stereo composite signal, the signal to the VCO FM modulation. This shows that the stereo composite signal before the generation is digitized, and then analog FM transmitter is no different. Referred to as "DSP+PLL".
3, Digital FM Transmitter: from audio to RF whole process of digital FM broadcast transmitter, it uses software radio technology to achieve FM broadcast transmitter. It receives digital audio signal (AES/EBU) or analog audio signal (into a/d), audio signal processing, stereo coding by DSP (digital signal processor) to complete, while the FM modulation process DSP control DDS (direct digital frequency synthesizer) to complete, the modulation process to achieve the digitization. The discrete digital FM is produced by D/A conversion to produce the conventional FM wave for the RF amplifier to enlarge to the specified power. Referred to as "Dsp+dds".
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