1. Communication Systems ๐ก
Modulation Types
| AM | Amplitude varies with message. BW = 2fm |
| FM | Frequency varies. BW โ 2(ฮf + fm) |
| PM | Phase varies. Similar to FM |
| Digital | ASK, FSK, PSK, QAM |
Transmission Parameters
Channel Capacity: C = Bยทlogโ(1 + S/N) (Shannon)
Nyquist Rate: fs โฅ 2fmax
dB = 10ยทlogโโ(Pโ/Pโ) = 20ยทlogโโ(Vโ/Vโ)
2. Antenna Theory ๐ถ
| Parameter | Definition | Unit |
|---|---|---|
| Gain | Power focused vs isotropic | dBi |
| Directivity | Max radiation / average | dB |
| Beamwidth | Angular width at half power | degrees |
| VSWR | Standing wave ratio (match) | ratio |
Common Antennas:
Dipole (ฮป/2): 2.15 dBi | Yagi: 7-20 dBi | Parabolic: 20-40 dBi
3. Control Systems ๐๏ธ
Transfer Function
G(s) = Output(s)/Input(s)
- Poles: denominator roots
- Zeros: numerator roots
- Stable: all poles in LHP
Stability Analysis
- Routh-Hurwitz: stability test
- Bode plot: gain/phase margins
- Root locus: pole movement vs gain
PID Controller
Gc(s) = Kp + Ki/s + Kds
P: proportional response | I: eliminate steady-state error | D: anticipate and damp
4. Microwave & RF ๐ป
Transmission Lines
Characteristic Impedance: Zโ = โ(L/C)
Reflection Coefficient: ฮ = (ZL - Zโ)/(ZL + Zโ)
VSWR = (1 + |ฮ|)/(1 - |ฮ|)
Perfect match: ZL = Zโ โ ฮ = 0, VSWR = 1
Waveguides
Cutoff frequency: fc = c/(2a) for TEโโ mode
Only propagates f > fc
Used in microwave systems (GHz range)
5. Instrumentation ๐ฌ
Measurement Concepts
Accuracy vs Precision:
Accuracy: closeness to true value
Precision: repeatability
Error Types:
Systematic: consistent offset
Random: statistical variation
Common Sensors:
Temperature: RTD, thermocouple, thermistor
Pressure: strain gauge, piezoelectric
Position: potentiometer, encoder, LVDT
6. Practice Questions ๐
Common Board Exam Questions
Q1: An AM signal has fc=1MHz, fm=10kHz. What is the bandwidth?
A: BW = 2fm = 2 ร 10kHz = 20kHz
Q2: A 50ฮฉ line is terminated with 75ฮฉ. Find VSWR.
A: ฮ = (75-50)/(75+50) = 0.2. VSWR = (1+0.2)/(1-0.2) = 1.5
Q3: A channel has 3kHz bandwidth, S/N = 1000. Find capacity.
A: C = 3000 ร logโ(1001) โ 3000 ร 9.97 โ 29.9 kbps
๐ฅ ECE Challenge ๐ฅ
Master systems! Communications, control, RF - connect and automate the world!
Systems thinking: see the big picture!