EC03 · Sem 5 · Digital signal processing

Window functions and spectral leakage

Aim: Compare rectangular, Hann, Hamming and Blackman windows.

🧪 Live simulation🧊 Real-time 3D bench⚠ Simulated values, not physical measurements

🔬 Virtual lab

Starting the lab…

📘 Theory

Cutting a signal into a finite block is the same as multiplying by a rectangular window, whose sidelobes leak energy. Tapered windows lower the sidelobes at the cost of a wider main lobe.

Hann: w[n] = 0.5 − 0.5·cos(2πn/(N−1))

🧰 Apparatus (virtual)

Square-wave source
FFT analyser with selectable window

📝 Procedure

Select the square wave and the rectangular window
Switch to Hann and compare the noise floor between harmonics
Try Blackman
Choose the best window for finding a weak tone next to a strong one

Observations and result (kept on this device)

🎤 Viva questions

Which window has the lowest sidelobes of the four

Blackman.

Why does a square wave show only odd harmonics

Its half-wave symmetry cancels the even ones.

🛡️ Safety

Virtual lab. With real RF equipment, respect exposure limits, never transmit without a licence, and keep antennas away from people.