In: Electrical Engineering
Almost all FM radio stations transmit digital FM signal. Explain how the fully analog FM has been converted to fully digital FM.
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A Fully Analog FM can be converted into a Fully Digital FM using the technologies-
(i)Conversion to IF using Super Heterodyne Receiver.
(ii)Conversion by RF Sampling.
This is the Block Diagram of a Super- Heterodyne Receiver showing how is RF sample works?
Components mentioned in the Block Diagram
BPF-Band Pass Filter
LNA- Low Noise Amplifier
Mixer
LO- Local Oscillator
IF Amplifier- Intermediate Frequency Amplifier
(i)Conversion to IF using Super Heterodyne Receiver.
In a Super heterodyne Receiver, after receiving the signal at RF frequencies, it mix the signal with the carrier signal from local oscillator and get a lower intermediate frequency (IF) which which will be a fixed frequency as a lot of filters are used in the bloc diagram. So, to tune it correctly we fix a frequency to IF then goes to the bandpass filter and goes to the Analog to digital converter and gets demodulated after that.
(ii) Conversion by RF Sampling
Unlike Super heterodyne receiver, Direct RF sampling receiver digitalize the signal directly with a RF ADC without converting it into Lower Intermediate Frequency(IF) or Zero Intermediate Frequency(IF). However, consists of just a low-noise amplifier, Filter and ADC. The purpose of LNA is to boost the signal to a level above the noise(to cancel it).
Because of less hardware complexity and lower design cost RF samping is prefered.
Hope that helps :).