Electronics Systems and Technologies: Signals, Comms, and Control
What to expect
This domain joins communication systems, signals and systems, control, and instrumentation. You need the sampling theorem (f_s at least twice the highest signal frequency), aliasing and quantization error, AM bandwidth (twice the modulating frequency) and FM Carson's rule, decibel and dBm arithmetic, transmission-line concepts (characteristic impedance, reflection coefficient, VSWR), antenna gain and the Friis path-loss relation, waveguide cutoff, fibre attenuation and numerical aperture, and the OSI layering plus standard error-detection schemes. From control: transfer functions, poles in the left half-plane for stability, damping ratio and overshoot, steady-state error, and PID action. From instrumentation: bridge circuits, sensor types, and ADC resolution.
Traps
- Confusing dB with dBm; dBm is an absolute power referenced to 1 mW (0 dBm = 1 mW), dB is only a ratio.
- Converting a decibel signal-to-noise ratio incorrectly: 30 dB is a linear power ratio of 1000, not 30.
- Using the Shannon formula with a logarithmic SNR value; the formula needs the linear ratio.
- Setting the sampling rate equal to the maximum frequency; it must be at least twice.
- Reading VSWR from the reflection coefficient without the magnitude: VSWR = (1 + |Γ|)/(1 − |Γ|).
Worked example
A 3 kHz channel has a 30 dB signal-to-noise ratio. Linear SNR = 10^(30/10) = 1000. Capacity C = B log2(1 + SNR) = 3000 × log2(1001) ≈ 3000 × 9.97 ≈ 29.9 kbit/s.
Rule of thumb
Always convert decibels to linear ratios before substituting into capacity, noise-figure, or link-budget equations - and convert back only at the end.