Correction done in circuit diagram of PAM using transistor

Added a missing resistor at the base of the transistor.
Modified the demodulator diagram as per the design.
Circuit diagram for PAM generation using IC modified

The connections for Vcc and GND are added to the IC 4016. The default
4016 IC component in geda has no provisions for them. Just addded a line
and indicated the pin numbers using text entry options in geda. A better solution may be required.
Miscellaneous edits in DSBSC using 633 IC

Content clarity enhanced. Filter design updated. COrresponding changes introduced
 in circuit diagram.