english_zf
.pdf
Professional language (english)
Speciality “Technical maintenanceof
transport radio equipment”
PART 1
Theoretical basics of radio technique
Simple radio technical system
Radio frequency (RF) is the number of cycles per second of radio wave, in hertz (Hz).
Transmitter (TX) is a device that converts electrical signals into emitted RF energy. It’s the source of a radiated wave.
Receiver (RX) is a device that receives RF energy and converts it back into electrical signals.
Propagation is the ability of radio wave to travel between a transmitter and a receiver in free space or in another medium such as air.
Antenna is a part of the transmitter or receiver system (or it can be in both). It is usually a passive device that converts electrical signals straight into radio waves.
Propagation of radio waves
Electromagnetic wave propagation vectors
Electromagnetic waves have three perpendicular vectors describing their generation:
•E is an electric field vector;
•H is a magnetic field vector;
•v is the propagation field vector
Speed propagation, wavelength and frequency
v = f • λ |
or c = f • λ, |
(in free space) |
where
• v is the velocity (m/s)
•f is the frequency (Hz)
•λ is the wavelength (m)
•c = 3 •10 8 m/s is the speed of light
Power, amplitudes and decibel rates
In radio technique there are considered dynamic ranges, for example, for power levels, power losses, signal voltages and fields strengths. Typically, for power the span can be from 10-12 up to 1016 W. Hence, the logarithmic scale is often used (or so called decibel scale) with the base of 10.
For power
dB (unit x) = 10 log10 (unit x)
dBW(unit x) = 10 log10 P (watts)
dBm(unit x) = 10 log10 P (milliwatts)
dBm(unit x) = 10 log10 P (watts) + 30
For amplitudes (e.g. voltage, current, field strength)
dB (unit x) = 20 log10 (unit x)
maintenance basics frequency radio wave device radio signal transmitter receiver propagation source radiated antenna medium rfenergy
List of words
vector dynamic range power voltage
span unit convention
wavelength losses scale strength
Nautical mile (NM)
The world is split up to into 360 of longitude and latitude; each degree is 60 NM and each minute is 1NM at earth’s surface.
The nautical mile is a unit length used for navigation that is equivalent to 1 minute of latitude extended at earth’s surface.
Nautical mile is a nautical unit of linear measure equal to 1,852
kilometres.
Mile (ordinary) is equal to 1,609 km.
Propagation of electromagnetic waves
In the radio engineering the free space is used as a transfer channel. This is the earth's atmosphere mainly. The distance between transmitter and receiver is always very large opposite the wavelength of the emitted energy.
The knowledge of the factors which influence the propagation of electromagnetic waves is importantly to the understanding of phenomena and measures which appear in the radio traffic.
Discussion has so far been mainly concentrated on how waves propagate in free space with line of sight (LOS) conditions. This describes the majority case for aviation and most situation can be approximated to this.
Occasionally, an aircraft will not have LOS to the nearest ground. This is usually the case on a long approach, or approach in mountainous terrain or transmitter (receiver) is over the horizon. At such lower altitudes other propagation mechanisms can come into effect, such as reflection, refraction, ground wave/sky wave.
Refraction
Radio waves passing through the atmosphere are affected by certain factors, such as temperature, pressure, humidity, and density. These factors can cause the radio waves to be refracted as they move from one medium into another in which the velocity of propagation is different. Refraction occurs when a wave travelling through two different mediums passes through the boundary of the mediums and bends toward or away from the normal.
Law of Refraction describes the relationship between the incident and the refracted rays when light rays encounter the boundary between two different transparent materials.