Approximate reproduction of images and text from the blackboard

A carrier wave:

A modulating signal:

Amplitude modulation:

Frequency modulation:

Two signals with the same frequency and power, but different phase

Bit stuffing example

data: 1010111101111100
send: 101011110011110100
(the bits in bold face have been stuffed, i.e. inserted)

Internet Checksum Example

Data is: 14 63 AB 32 46 17 Checksum 

    1464
    AB32
    4617
    ----
  1 05AC
       1
    ____
    05AD
The inverted checksum is FA 52 . Verifying the checksum: 
    1464
    AB32
    FA52
    4617
    ----
  1 FFFE
       1
    ____
    FFFF

CRC shift register