Radio Communication Essentials and Propagation
Radio Communication
Radio communication takes place via radio waves that carry electric voice and video data. It is very important that the frequency of the radio system is correct.
Communication, Emission, and Propagation
- Transmission of electrical signals
- Reception
Radio Communication Services
- Fixed point-to-point service
- Mobile services (between stations)
- Channel broadcasting (radio and TV)
Simple Method of Operation
- One-way transmission
- Duplex: Simultaneous transmission in one way
- Half-duplex: Simultaneous transmission in one direction, but at different times
Parameters of Radio Communication
- Bandwidth needed
- Broadcast type
- Transmission power
- Type of polarization
- Occupied bandwidth
- Variation in the frequency of unwanted emissions
Transmission Denomination
- Alphanumeric class type
- Emission type
- Modulation (natural type)
- Modulated signal
- Additional features
- Information
- Multiplexing characteristics
Physical Phenomena
- Reflection
- Refraction
- Diffraction
- Dispersion
- Absorption
Reception Intensity Parameters
- Ultra-bright field
- Usable field condition
- Reception interference ratio
- Protective operating parameters
- Area coverage of service area transmission
Transmission Energy Model
- Circuit
- Circuit coupling the antenna
- Transmission antenna
- Reception antenna
- Circuit
- Circuit coupling antenna
- Reception
Interference
- Noise (natural noises: internal, external, and artificial)
- Co-channel interference
- Underlying simplex multiplex
- Channel subject to interference
Limited Power Systems
Interference-limited systems: Performance depends on the reception power.
Radio Propagation
Radio propagation, as the OEM, depends on geographical and topographical obstacles, and anisotropic electromagnetic physical characteristics that are frequency-dependent. For short distances, the curvature of the Earth is not considered.
Wave Propagation Modes
- Direct
- Troposphere
- Ionosphere
- Surface
Depending on the shape of the diffraction edges, obstacles can be “acute” or “round”.
Attenuation by Vegetation
This is given for frequencies of 3 MHz. If the loss exceeds 30dB, it is considered lost to diffraction.
Attenuation by Atmospheric Gases and Vapors
O2 and H2O molecules absorb electromagnetic energy.
Rain Attenuation
Due to absorption by rain and hail, it should be evaluated by the rain during a small percentage of time. Excessive at 6MHz.
Signal Fading
This is the diminution of the power received with respect to its nominal value.
Classification of Fading
- Plane
- Selective
- Multipath (factor k)
Propagation in the Ionosphere
f = 1.5 – 30 MHz; Layers: D, E, F (vary with time of day).
Terrestrial Radio Link
This is the interconnection between central stations.
Depending on the Type
- Analog (QPSK, QAM modulation)
- Digital (hierarchy of 2 Mbps speed)
Depending on Capacity
- Low capacity: 2 Mbps, 32 analog channels
- Medium capacity: 8 Mbps, 240 analog channels
- High capacity: 34 Mbps, 300-2700 analog channels
Advantages and Disadvantages
- Lower cost than terrain
- Restricted maintenance
- Quick installation
General Structure of the Radio Link
- Equipment
- Reserve elements
- Supervision systems
- Frequency plans (2-frequency and 4-frequency plans)
Plan Considerations
- Number of radio links
- Separation between frequencies
- Guard band
- Frequency values
- Bandwidth
- Polarization
- Multipath fading
Analog
- Intermodulation noise
- Digital inter-symbol interference
- Carrier recovery interference
- Timing recovery