The AM demodulator detector is an electronic circuit used to recover the information content from the modulated carrier wave. Demodulation is called the process recovering AF signal from modulated carrier wave. The AM demodulation of an AM wave involves two operations:
i) rectification of the modulated wave .
ii) Elimination of the RF component of the modulated wave.
Thus an AM receiver or detector is electronic equipment which picks up the desired signal, rejects the unwanted signal, amplifies the desired signal, and demodulates the carrier to get back the original modulation frequency signal.
Classification of AM Broadcast receivers receiver:
- A.M(Amplitude Modulation) Broadcast receivers
- F.M (Frequency Modulation) Broadcast receivers
- T.V(Television) Receivers
- Communication Receivers
- Color Receivers
- Radar Receivers.
Salient feature of AM broadcast receiver:
- Simplicity of Operation
- Good Fidelity
- Good Selectivity
- Average Sensitivity
- Adaptability to different types of aerials.
Basic Functions of A.M Receiver:
- Detection or Demodulation
Based on the technique of operation AM detector or receiver may be put
- Straight receiver i.e. receiver which operate in straight forward manner without frequency conversion
- Super-heterodyne receivers, in which incoming radio-frequency (R.F) signal is converted to standard Intermediate frequency (I.F) before detection take place.
Transistor can be used as detector amplifier i.e. both for rectification and amplification. The amplification of the recovered signal takes place in the emitter collector circuit. It should be noted that when used as a detector, the transistor has to be biased at cut-off or operated as class-B.
- C2 ac grounds R3 whereas voltage divider R1-R2 establishes proper bias which holds the transistor just at cut-off.
- The rectified signal appears across Rc-C3 combination.
- C3 eliminates RFD component so that only AF signal voltage drops RC.
- The capacitor C4 permits AF signal to pass through but block its dc component.