- Tune- radio
- Super-hetero dyne radio
Tune radio is an old type of radio system It connect only one channel at a time . Because of tune of RF signal process it has more distortion ,less efficiency ,more noise and interference .So this type of radio is not good in the broadcasting system .
Super-hetero dyne radio type of radio principle is modern type of technology .It contain mixer , local oscillator ,RF filter in one circuit which help to trap the RF constant frequency .at the out put of mixer .So it tune accurate channel . It reduce to RF signal return back from mixer through antenna.So it is high efficiency ,less distortion and less interference , low noise in this type of broadcasting.
It is a simplex communication system It means it transmit RF signal from transmitter site to receiver site. So we only able to listen but dose not reply from receiver site .So this type of communication is known as one way communication system.
Radio work at short wave(SW) frequency and medium wave (MW) frequency.
There are three type of signal in radio communication:
- carrier signal
- Modulating signal (audio signal or base band signal)
- modulated signal
There are three type of modulation:
- Amplitude modulation
- Frequency modulation
- Phase modulation
In amplitude modulation ,amplitude of carrier signal is change according to amplitude of modulating signal.Here other characteristics like frequency and phase remain unchanged .This type of modulation system is known as amplitude modulation.
In FM,frequency of carrier signal is varies according to the frequency of audio signal whereas other i.e amplitude and phase remain unchanged.This type of modulation is known as frequency modulation.
In PM,phase or angle of carrier signal is change according to phase of audio signal and other i.e frequency and amplitude remain unchanged.
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