This device is just another mixer - used for demodulating a signal in a receiver. The term "product" refers to the multiplication of the two input signals - with sum and difference outputs.
In the product detector the product signal ie, the dual sideband or single side band signal is again multiplied with the local carrier .
NOTE
In case of suppressed carrier systems (dont confuse carrier fully suppressed)
there is a need to get the carrier at the receiver at same frequency as that of the transmitter and the phase must be same.Hence we need highly stable oscillators free from drift.Such a process called synchronization must be done at the receiver ,which makes the receiver complex.For these reasons a pilot carrier system is preferred ,where the carrier is generated by the LO referring to the pilot carrier.
Receiver blockdiagram is available
here
In the case of AM signals a synchronous demodulator is preferrable because it offers more stability to the s/n ratio.In the synchronous demodulator we multiply the signal received by the
locally generated carrier hence the signal can be recovered
At the modulator side ,
Sin(Wct)Cos(Wmt)+Cos(Wct)Sin(Wmt)=Sin((Wc-Wm)t) {the modulated signal}
or the side band corresponding to upper frequencies.
where the Cos(Wmt) is obtained from Sin(Wmt) or vice versa thro Hilbert's Transform.
At the demodulator side,
Sin(Wct)Cos(Wmt)+Cos(Wct)Sin(Wmt)=Sin((Wc-Wm)t)
is multiplied by Sin(Wct)
so that a (Sin(Wct))square term appears which can be expressed interms of double angle
by the trig relation sothat the signal Cos(Wmt) can be filters at the output by using alow pass filter
In the product detector the product signal ie, the dual sideband or single side band signal is again multiplied with the local carrier .
NOTE
In case of suppressed carrier systems (dont confuse carrier fully suppressed)
there is a need to get the carrier at the receiver at same frequency as that of the transmitter and the phase must be same.Hence we need highly stable oscillators free from drift.Such a process called synchronization must be done at the receiver ,which makes the receiver complex.For these reasons a pilot carrier system is preferred ,where the carrier is generated by the LO referring to the pilot carrier.
Receiver blockdiagram is available
here
In the case of AM signals a synchronous demodulator is preferrable because it offers more stability to the s/n ratio.In the synchronous demodulator we multiply the signal received by the
locally generated carrier hence the signal can be recovered
At the modulator side ,
Sin(Wct)Cos(Wmt)+Cos(Wct)Sin(Wmt)=Sin((Wc-Wm)t) {the modulated signal}
or the side band corresponding to upper frequencies.
where the Cos(Wmt) is obtained from Sin(Wmt) or vice versa thro Hilbert's Transform.
At the demodulator side,
Sin(Wct)Cos(Wmt)+Cos(Wct)Sin(Wmt)=Sin((Wc-Wm)t)
is multiplied by Sin(Wct)
so that a (Sin(Wct))square term appears which can be expressed interms of double angle
by the trig relation sothat the signal Cos(Wmt) can be filters at the output by using alow pass filter