Textbook Study Note

Chapter 1 Radio Technology

1.1 Introduction

Telemetry: long distance

Communications: wireless, wired or cable

Radio communication links

Data rate

Radio spectrum:

Sub-GHz: RF or radio

Above 1GHz: microwave

1.2 Fundamentals of radio operation

Electromagnetic waves: electric field, magnetic field

Frequency: Hz (hertz)

Radiation, radiator

Antenna

Wavelength

Free space

Speed of light (propagation)

Wavelength and propagation (penetration)

Short wavelength: 300-900MHz

Long wavelength: 1-300MHz

1.2.1 Components of a radio link

Antennas, transmitteres, receivers, antenna support structures, cabling, interface equipments

Antenna support structure: masts, guys, towers

Cabling: coaxial, twisted pair, power cables

1.3 The radio spectrum and frequency allocation

1.3.1 General

Radio spectrum for public use:

HF: 2-30MHz

Low VHF: 30-60MHz

Mid VHF: 60-100MHz

High VHF: 100-300MHz

Low UHF: 300-600MHz

High UHF: 600-900MHz

1.3.2 Single and two frequency systems

Channel bandwidth: 12.5kHz or 25kHz

Simplex: single frequency, single direction or two-direction

Duplex: two-frequency, 5MHz spacing

Half duplex: f1 for Tx in one direction, f2 for Tx in the other direction; only one Tx at a time, application = radio repeater

Full duplex: f1 for Tx1, f2 for Tx2, f1 and f2 radiate simultaneously

1.4 Gain, level, attenutation and propagation

1.4.1 Gain and loss

(gain)

1.4.2 Level

1.4.3 Attenuation

30dBm → 25dBm: Attenuation 5dB, gain –5dB

1.4.4 Propagation

Propagation-related factors:

Frequency

Terrain

Time of year

Weather

Moisture and salt content of the terrain

Distance of propagation

Antenna heights

Antenna types and polarization

1.4.4.1 Surface wave

Travel across the surface of the earth

Surface wave = ground wave: < 3MHz

Ground wave attenuation

Ground wave reception with a Beverage antenna

Long-distance LF longwave radio: 30-300kHz, ground wave propagation only

Medium wave: 0.3-3MHz, both ground wave and skywave (for longer distances)

HF: 2-20MHz, sea surface wave for up to 100km, skywave for longer distances

1.4.4.2 Ionospheric reflection and scatter

Ionosphere: 10⁴ - 10⁶ electrons/cm³

Ionospheric reflection

Skywave communicationi: 3-30MHz by ionospheric reflection, above 30MHz no reflection by ionosphere

Scatter communication: multiple reflections between earth and ionosphere

1.4.4.3 Ionospheric refraction

1.4.4.4 Tropospheric (대류권) scatter

1.4.4.5 Line of sight (LOS)

Fresnel zone: a series of confocal prolate ellipsoidal regions between Tx and Rx

- Can help to predict whether obstructions or discontinuities along the path will cause significant interference.

- N half-wavelength out of phase with the straight-line path: destructive interference

Two-ray model:

1.4.4.6 Diffraction

1.4.4.7 Ducting