Modulated signal from noise separator - uses square wave multiplication, integration and pass band filtering

摘要

The system extracts an amplitude modulated signal of the form s(t) = Asin(Wrt-phi)CoswHt where wH>>wr, from the detector output which includes a noise term B(t). This is achieved by multiplying the compound signal F(t)=S(t)+ B(t) by a phase locked square wave g(t) derived from the high frequency carrier (WH). The square wave is defined as g(t)=0 for piWH2pi and g(t)=1 for 0WHtpi. The product U = F(t) x g(t) is passed to an integrator of time constant 2pi/WHtau2pi/W and thence to a passband filter centred on Fr whose band width may be selected. The final output contains only the envelope ASin (W rt = phi). The noise pass band can be reduced by filter selectivity and the system may be used as the basis of a phasemeter.