EC08 · Sem 5 · Analog communication

Frequency modulation (FM)

Aim: Generate FM and estimate its bandwidth with Carson’s rule.

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

🔬 Virtual lab

Starting the lab…

📘 Theory

The carrier frequency swings with the message; the index β = Δf/fm sets how many significant sidebands appear (Bessel functions). Carson’s rule gives the bandwidth as 2(β + 1)fm.

BW ≈ 2·(β + 1)·fm · β = Δf / fm

🧰 Apparatus (virtual)

Carrier 2 kHz
message 100 Hz
FM modulator
spectrum analyser

📝 Procedure

Run with β = 3 and count the significant sidebands
Compare with Carson’s rule
Lower β to 0.3 (narrow-band FM)
Listen to the scaled signal

Observations and result (kept on this device)

🎤 Viva questions

Why is FM less sensitive to noise than AM

The information is in the frequency, and amplitude noise can be clipped away.

What is the FM broadcast deviation in India

75 kHz.

🛡️ Safety

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