Telecommunication Fundamentals and Signals
Telecommunication Fundamentals and Signals
This domain tests signal behaviour in telecom: frequency, period, wavelength, bandwidth, analog and digital forms, modulation, decibels, noise, sampling and channel capacity. Questions often ask you to convert units or choose the correct modulation for a link.
Core rules
- Frequency f and period T are reciprocals: T = 1/f. Wavelength λ = v/f; in free space v ≈ 3×10^8 m/s.
- Bandwidth is the range of frequencies a channel carries, not the bit rate, although they are related by modulation and coding.
- Decibel gain is 10 log10(Pout/Pin) for power and 20 log10(Vout/Vin) for voltage; dBm is an absolute power referred to 1 mW.
- Analog signals vary continuously; digital signals use discrete levels. Sampling must exceed twice the highest frequency (Nyquist) to avoid aliasing.
- Modulation shifts a baseband signal onto a carrier: AM varies amplitude, FM varies frequency, and ASK/FSK/PSK are digital equivalents.
Worked example
A 100 MHz carrier has T = 1/(100×10^6) = 10 ns and λ = 3×10^8/100×10^6 = 3 m. If a channel has 20 MHz bandwidth and uses 4-level signalling, a simplified ideal rate is 2 × 20 MHz × log2(4) = 80 Mbit/s. The reasoning uses Nyquist for a noiseless channel; real links are lower because of noise, filtering and coding overhead.
Traps that cost marks
Confusing dB with dBm; treating bandwidth as bit rate; using 10 log for voltage ratios; forgetting that sampling rate must be above 2fmax; and mixing up FM with PM. Also watch prefixes: MHz is 10^6 Hz, not 10^3.