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Analog Electronics
The centre tapped tuned circuit is very hghtly
coupled to the collector tuned circuit, so the
reference voltage is in quadrature with the voltage
across the centre tapped tuned circuit. The result-
ing voltages applied to the detector diodes are as
indicated by the vector diagrams. Capacitors C
have a value of around 330 pF, so that they present
a very low impedance at the usual FM IF of
10.7 MHz but a very high impedance at audio
frequencies. As the detected output voltage from
one diode rises, that from the other falls, so that
the recovered audio appears in antiphase across /?,
and /?2, whilst the voltage across C