MICROWAVE RADIO COMMUNICATIONS AND SYSTEM GAIN (c22 Tomasi)

CHAPTER 24
MICROWAVE RADIO COMMUNICATIONS AND SYSTEM GAIN

1)Electromagnetic waves with frequencies that range from approximately 500 MHz to 300 GHz or more.
Microwaves

2)The wavelengths for microwave frequencies, which is than infrared energy.
1 cm and 60 cm slightly longer

3)The name given to microwave signals, because of their inherently high frequencies, have short wavelengths.
“Microwave” waves

4)Each frequency is divided in half with the lower half identified as the low band and the upper half as narrow band.
Full-Duplex (Two-way)

5)Communications system used to carry information for relatively short distances such as between cities with the same state.
Short Haul

6)Microwave systems that is used to carry information for relatively long distances, such as interstate and backbone route applications.
Long Haul

7)It propagate signals through Earth’s atmosphere between transmitters and receivers often located on top of tower spaced about 15 miles to 30 miles apart.

Microwave Radios 

Advantages of Microwave Radio:
 Radio systems do not require a right-of way acquisition between stations.
 Each station requires the purchase or lease ofonly a small area of land.
 Because of their high operating frequencies, microwave radio systems can carry large quantities of information.
 High frequencies mean short wavelengths, which require relatively small antennas.
 Radio signals are more easily propagated around physical obstacles such as water and high mountains
 Fewer repeaters are necessary for amplification.
 Distances between switching centers are less.
 Underground facilities are minimized.
 Minimum delays are introduced.
 Minimal crosstalk exists between voice channels.
 Increased reliability and less maintenance are important factors.
Disadvantages of Microwave Radio:
 It is more difficult to analyze and design circuits at microwave frequencies.
 Measuring techniques are more difficult to perfect and implement at microwave frequencies.
 It is difficult to implement conventional circuit components at microwave frequencies.
 Transient time is more critical at microwave frequencies.
 It is often necessary to use specialized components for microwave frequencies.
 Microwave frequencies propagate in a straight line, which limits their use to line-of-sight applications.

8)Propagates signals outside the Earth’s atmosphere and are capable of carrying signals much farther while utilizing fewer transmitters and receivers.
Satellite Systems

9)It is used in microwave radio systems rather than amplitude modulation because AM signals are more sensitive to amplitude nonlinearities inherent in wide-band microwave amplifiers.
Frequency Modulation

10)Major factor when designing FM Radio systems. It is caused by repeater amplitude nonlinearity in AM, while in FM, it is caused by transmission gain and delay distortion.
Intermodulation Noise

11)The composite signal that modulates the FM carrier and may comprise one or more of the following:
 Frequency-division multiplexed voice-band channels
 Time-division-multiplexed voice-band channels
 Broadcast-quality composite video or picture phone
 Wideband data
Baseband

12)It provides an artificial boost in amplitude to the higher baseband frequencies.
Preemphasis Network

13)Frequency modulation index used in the FM deviator. Typically, modulation indices are kept between 0.5 and 1.
Low-Index 

14)FM signal that is produces at the output of the deviator with a low-index frequency modulation.
Narrowband FM

15)A receiver and a transmitter placed back to back or in tandem with the system.
Microwave Repeaters

16)It receives a signal, amplifies and reshapes it, and then retransmit the signal to the next repeater or terminal station down line from it.

Repeater Station
Types of Microwave repeaters:
 IF
 Baseband
 RF

17)The received RF carrier is down-converted to an IF frequency, amplified, reshaped, up-converted to an RF frequency, and then retransmitted.
IF Repeater

18)Generally less than 9 MHz.
Baseband Frequencies

19)The range id 60 MHz to 80MHz.
IF frequencies

20)Another name for a Local oscillator, is considerably lower in frequency than either the received or the transmitted radio frequencies.
Shift Oscillator

21)Transmission used by microwave systems wherein a direct signal path must exist between the transmit receive antennas.
Line-of Site Transmission

22)A temporary reduction in signal strength which last in milliseconds for several hours or even days.
Radio Fade

23)It suggests that there is more than one transmission path or method of transmission available a transmitter and a receiver.
Diversity

24)It is simply modulating two different RF carrier frequencies with the same IF intelligence, then transmitting both RF signals to a given destination.
Frequency Diversity

25)The output of a transmitter is fed to two or more antennas that are physically separated by an appreciable number of wavelengths.
Space Diversity

26)A single RF carrier is propagated with two different electromagnetic polarizations. It is generally used in conjunction with space diversity.
Polarization Diversity

27)It is more than one receiver for a single radio-frequency channel. With frequency diversity, it is necessary to also use receiver diversity because each transmitted frequency requires its own receiver
Receiver Diversity

28)Another form of Hybrid diversity and undoubtly provides the most reliable transmission but most expensive. It combines frequency, space, polarization and receiver diversity into one system.
Quad Diversity

29)A specialized form of diversity that consist of a standard frequency diversity path where the two transmitter/ receiver pairs at one end of the path are separated from each other and connected to different antennas that are vertically separated as in space diversity.
Hybrid Diversity

29)Alternate facilities temporarily made to avoid a service interruption during periods of deep fades or equipment failures.
Protection Switching Arrangement

types of protection switching arrangements:
 hotstandby
 diversity

30)Each working radio channel has a dedicated backup or spare channel.
Hot Standby Protection

31)A single backup channel is made available to as many as 11 working channels.
Diversity Protection

32)In hotstandby protection, it splits the signal power and directs it to the working and the spare (standby)microwave channels simultaneously.
Head-End Bridge

33)It has two working channels, one spare channel, and an auxiliary channel.
Diversity Protection

34)A low-capacity low-power microwave radio that is designed to be used for a maintenance channel only.
Auxilliary Channel

35)It is where the number of repeater stations between protection switches depends.
Reliability Objectives of the Systems

36)Points in the system where baseband signals either originate or terminate.
 Terminal Stations

four major sections:

 baseband
 wireline entrance link (WLEL)
 FM-IF
 RF sections

37)Points in a system where baseband signals may be reconfigured or where RF carriers are simply “repeated” or amplified.
Repeater Stations

38)Stands for WireLine Entrance Link, it serves as the interface between the multiplex terminal equipment and the FM_IF equipment.
WLEL

39)A balanced modulator that, when used in conjunction with a microwave generator, power amplifier, and band-pass filter, up-converts the IF carrier to an RF carrier and amplifies the RF to the desired output power.
Transmod

40)It must be capable of amplifying very high frequencies and passing very wide bandwidth signals for microwave radios.
Power Amplifiers

devices used in microwave amplifiers:
 Klystron Tubes
 Traveling-wave tubes (TWTs)
 IMPATT (Impact avalanche and transit time)

41)It provides the RF carrier input to the up-converter. It is called as microwave generator rather than an oscillator because it is difficult to construct a stable circuit that will oscillate in the gigahertz range.
Microwave Generator

42)It operates in the range 5 MHz to 25 MHz, used to provide a base frequency that is multiplied up to the desired RF carrier frequency.
Crystal-controlled Oscillator

43)A unidirectional device often made from ferrite material. It used in conjunction with a channel-combining network to prevent the output of one transmitter from interfering with the output of another transmitter.
Isolator

44)Stands for Automatic Gain Control, is a circuit in an IF amplifier.
AGC

45)It occurs only when three stations are placed in a geographical straight line in the system.
Multi-hop Interference

46)It prevents the power that “leaks” out the back and sides of a transmit antenna from interfering with the signal entering the input of a nearby receive antenna.
High/Low-Frequency Scheme

47)The signal entering the input of a nearby receive antenna.
Ring around

48)It means that this channels are propagated with vertical polarization.
V Channels

49)The line-of-sight directly between the transmit and receive antenna. Also called as the Direct Wave.
Free-Space Path

50)It consists of the electric and magnetic fields associated with the currents induced in earth’s surface.
Surface Wave

51)The portion of the transmit signal that is reflected off Earth’s surface and captured by the receive antenna.
Ground-Reflected Wave

52)The portion of the transmit signal that is returned back to Earth’s surface by the ionized layers of earth’s atmosphere.
Sky Wave

53)The loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection of energy from nearby objects.
Free-Space Path Loss

54)A phenomenon wherein electromagnetic energy is spread out as it propagates away from the source resulting in lower relative power densities.
Spreading Loss

55)The reduction in signal strength at the input to a receiver.
Fading

56)The difference between the nominal output power of a transmitter and the minimum input power to a receiver necessary to achieve satisfactory performance.
System Gain

57)Sometimes called as Link Margin, is essentially a “fudge Factor” included in system gain equations that considers the non ideal and less predictable characteristics of radio wave propagation and terrain sensitivity.
Fade Margin

58)He described ways of calculating outage time due to fading on a non diversity path as a function of terrain, climate, path length, and fade margin, in April 1969.
W.T. Barnett
59)From Bell Laboratories, he derived formulas for calculating the effective improvement achievable by vertical space diversity as a function of the spacing distance, path length, and frequency in June 1970.
Arvids Vignant

60)The ratio of the wideband “carrier” to the wideband noise power.
Carrier-to-Noise Ratio (C/N)

61)Also called Receiver Sensitivity, is the minimum wide band carrier power at the input to a receiver that will
provide a usable baseband output.
Receiver Threshold

62)The carrier-to-noise ratio before the FM demodulator.
Pre-detection Signal to-Noise Ratio

63)The carrier-to-noise ratio after the FM demodulator.
Postdetection Signal-to-Noise Ratio

64)A ratio of input signal-to-noise ratio to output signal to noise ratio.
Noise Factor (F)

65)The noise factor stated in dB and is a parameter commonly used to indicate the quality of a receiver.
Noise Figure