Time domain · 0 to 1 samplitude (V)
Frequency domain · 0 to 12 Hzpeak amplitude
Three numbers describe a sine wave
Period T = 1/f
Try f = 0: the wave becomes a flat line (DC) and its spike moves to 0 Hz. Changing the phase moves the wave but never the spike.
Time domain · sum of harmonics vs ideal square wavef = 1 Hz
Frequency domain · odd harmonics onlyamplitude ∝ 1/n
Add sine waves until you get a square
Frequencies used
A perfect square wave needs infinitely many harmonics, so its exact bandwidth is infinite. In practice we keep the few that carry most of the shape: the significant bandwidth.
Sent (blue) and received (orange) signal · one repetition of the pattern
Spectrum of the sent signal · shaded = what the channel lets through
Does the channel have enough bandwidth?
Minimum B ≈ N/2
Lower B until the received bits start to break, then raise N. Faster bits need a wider channel.
Period and frequency
Bangladesh mains: T = 20 ms, so f = 50 Hz.
Wavelength
λ = propagation speed ÷ frequency.
Bit interval and bit length
Bit interval = 1 ÷ bit rate. Bit length = speed × bit interval.