Microwave Basics

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QAM

Subtopic

Bandwidth

Microwave Basics

Link fading (Dispersion)

Rain attenuation

Refers to scenarios where signal is absorbed by rain, snow, ice • Absorption becomes significant factor above 11GHz • Signal quality degrades • Represented by “dB/km” parameter which is related the rain density which represented “mm/hr” • Rain drops falls as flattened droplet  V better than H (more immune to rain fading)

Climatic

Terrain

Atmospheric (refraction)

Multipath/ducting

Multipath transmission is the main cause of fading in LOW frequencies

Multipath occurs when there is more then one beam reaching the receiver with different amplitude or phase

Humidity/Gas

Dispersion

Electromagnetic signal propagating in a physical medium is degraded because the various wave components (i.e., frequencies, wavelengths) have different propagation velocities within the physical medium: • Low frequencies have longer wavelength and refract less • High frequencies have shorter wavelength and refract more

Antennas

Modulation

Digital

QAM – Quadrature Amplitude modulation

PSK – Phase Shift Keying

FSK – Frequency Shift Keying

ASK – Amplitude Shift Keying

Analog

PM – Phase modulation

FM - Frequency modulation

AM - Amplitude modulation