Space Wave Propagation Questions and Answers

Q: Assertion (A): A microwave link is designed with clearance checked at two different k factors. Reason (R): Atmospheric refraction varies, and each extreme produces a different threat to the path. Select the correct answer from the options below.

Both are true and the second is the reason. Low k values bulge the earth and threaten clearance, while high k values flatten the ray and can create a strong ground reflection, so a design safe under standard conditions may fail under either extreme. That is why criteria are expressed as a pair of conditions rather than as a single one. Checking a design at the extremes of a varying parameter, rather than at its mean, is a general principle of robust engineering.

Q: Statement I: Rain attenuation increases with frequency. Statement II: Rain attenuation is effectively removed by frequency diversity. In the light of the above statements, choose the correct answer.

The first is correct and steeply so above ten gigahertz. The second is wrong, because rain attenuates a whole band nearly equally and two nearby carriers fade together, leaving no independence for diversity to exploit. Route diversity, with a second path outside the rain cell, is the effective answer. The pair illustrates that a countermeasure works only where the impairment it addresses is genuinely independent between the two branches.

Q: A microwave link fails for a few minutes on clear still nights but works perfectly in windy weather. What is the most likely cause?

Calm anticyclonic nights allow stratified layers to form, producing an additional refracted path that interferes with the direct one and causes deep, brief fades, while wind mixes the atmosphere and destroys the layering. Rain is excluded by the clear conditions, diffraction is a permanent loss, and interference would not correlate with wind. Correlating an outage with the weather that accompanies it is often enough to identify the mechanism without any instrumentation at all.

Q: Why does windy weather improve a link that suffers atmospheric multipath?

Layered structures require calm conditions to persist, and mechanical mixing breaks them up, removing the second path and with it the interference. That is why such fading is characteristically a still night phenomenon over water and flat ground. Cooling, rain removal and tower movement are not the mechanism. Knowing the meteorological conditions under which an impairment occurs allows its statistics to be predicted from climate data rather than measured over years.

Q: How does angle diversity work on a fixed radio path?

Two beams offset slightly in elevation receive the direct and the refracted paths with different relative amplitudes, so they fade differently and combining them restores availability, at less cost than a second antenna on a taller tower. Route diversity, crossing links and polarisation diversity are different arrangements. Any dimension along which two signals fade independently can be exploited, and elevation angle happens to be an effective one against atmospheric multipath.

Q: What is the general principle behind every diversity technique?

Diversity works only if the two branches are unlikely to be in a fade at the same moment, so the probability of an outage becomes the product rather than the sum of the individual probabilities. Space, frequency, angle, polarisation and route are simply different ways of obtaining that independence. Power doubling and noise averaging are different benefits, and selecting the better branch is one implementation among several. Independence, not duplication, is what buys the improvement.

Q: What frequency range is normally used for terrestrial line of sight links?

Fixed links occupy the bands from about two to forty gigahertz, with the lower bands used for long hops and the higher for short dense urban links. Below that the antennas would be unwieldy and the spectrum congested; above it, atmospheric absorption limits the range severely. High frequency bands are ionospheric rather than line of sight. Each part of the spectrum suits a range of hop lengths, and choosing the band is choosing the hop length.

Q: Why are lower microwave bands used for longer hops?

Below about ten gigahertz rain is almost irrelevant and gaseous absorption negligible, so a modest fade margin covers a hop of tens of kilometres. Antenna gain for a given size falls rather than rises at lower frequency, the Fresnel zone is wider, and regulation follows physics. The two disadvantages are accepted because the atmospheric advantage dominates on a long path, which is a good example of one term in a budget outweighing several others.

Q: Why are higher bands used for short urban links?

At thirty eight gigahertz a thirty centimetre dish gives high gain and narrow beams that allow dense reuse, and wide channels are available, which suits hops of a few kilometres between rooftops. Rain is a limitation rather than an advantage and is accepted because the hops are short. Building reflection is a nuisance, and lower bands can carry high rates given the spectrum. Matching the frequency to the hop length and the spectrum availability is the design decision.

71.

Three of the following are addressed by a fade margin. Which is the odd one out?

An obstacle permanently intruding into the Fresnel zone

Rain attenuation during a heavy shower

Multipath fading during still anticyclonic weather

Scintillation on a low elevation satellite path

A.Multipath fading during still anticyclonic weather
B.Scintillation on a low elevation satellite path
C.An obstacle permanently intruding into the Fresnel zone
D.Rain attenuation during a heavy shower

Answer: C

Rain, multipath and scintillation are time varying impairments whose statistics determine how large a margin must be. A permanent obstruction is a fixed loss that belongs in the budget itself rather than in the margin, and no amount of margin will make an obstructed path behave as a clear one. Distinguishing a constant term from a varying one decides whether it is subtracted once or covered statistically.

Discuss in Forum

72.

Assertion (A): A microwave link is designed with clearance checked at two different k factors.

Reason (R): Atmospheric refraction varies, and each extreme produces a different threat to the path.

Select the correct answer from the options below.

A.Both A and R are true, but R is not the correct explanation of A
B.A is true but R is false
C.A is false but R is true
D.Both A and R are true, and R is the correct explanation of A

Answer: D

Both are true and the second is the reason. Low k values bulge the earth and threaten clearance, while high k values flatten the ray and can create a strong ground reflection, so a design safe under standard conditions may fail under either extreme. That is why criteria are expressed as a pair of conditions rather than as a single one. Checking a design at the extremes of a varying parameter, rather than at its mean, is a general principle of robust engineering.

Discuss in Forum

73.

Statement I: Rain attenuation increases with frequency.

Statement II: Rain attenuation is effectively removed by frequency diversity.

In the light of the above statements, choose the correct answer.

A.Statement I is correct but Statement II is incorrect
B.Both Statement I and Statement II are correct
C.Both Statement I and Statement II are incorrect
D.Statement I is incorrect but Statement II is correct

Answer: A

The first is correct and steeply so above ten gigahertz. The second is wrong, because rain attenuates a whole band nearly equally and two nearby carriers fade together, leaving no independence for diversity to exploit. Route diversity, with a second path outside the rain cell, is the effective answer. The pair illustrates that a countermeasure works only where the impairment it addresses is genuinely independent between the two branches.

Discuss in Forum

74.

A microwave link fails for a few minutes on clear still nights but works perfectly in windy weather.

What is the most likely cause?

A.Interference from another link that operates only at night
B.Multipath fading from an atmospheric layer forming in calm conditions
C.Rain attenuation, which happens to coincide with calm weather
D.Diffraction loss from an obstacle that only matters at night

Answer: B

Calm anticyclonic nights allow stratified layers to form, producing an additional refracted path that interferes with the direct one and causes deep, brief fades, while wind mixes the atmosphere and destroys the layering. Rain is excluded by the clear conditions, diffraction is a permanent loss, and interference would not correlate with wind. Correlating an outage with the weather that accompanies it is often enough to identify the mechanism without any instrumentation at all.

Discuss in Forum

75.

Why does windy weather improve a link that suffers atmospheric multipath?

A.Wind blows the rain away from the path between the antennas
B.Movement of the towers averages out the fading over time
C.Mixing destroys the stratified layers that produce the extra path
D.Wind cools the antennas and improves the receiver performance

Answer: C

Layered structures require calm conditions to persist, and mechanical mixing breaks them up, removing the second path and with it the interference. That is why such fading is characteristically a still night phenomenon over water and flat ground. Cooling, rain removal and tower movement are not the mechanism. Knowing the meteorological conditions under which an impairment occurs allows its statistics to be predicted from climate data rather than measured over years.

Discuss in Forum

76.

How does angle diversity work on a fixed radio path?

A.Two antennas pointing at two different distant stations
B.Two links crossing at right angles at the same site
C.Reception on two polarisations from the same antenna
D.Two feeds at slightly different elevation angles on one antenna

Answer: D

Two beams offset slightly in elevation receive the direct and the refracted paths with different relative amplitudes, so they fade differently and combining them restores availability, at less cost than a second antenna on a taller tower. Route diversity, crossing links and polarisation diversity are different arrangements. Any dimension along which two signals fade independently can be exploited, and elevation angle happens to be an effective one against atmospheric multipath.

Discuss in Forum

77.

What is the general principle behind every diversity technique?

A.Combining signals whose impairments are statistically independent
B.Doubling the transmitted power by using two transmitters
C.Selecting the branch with the highest average signal level
D.Averaging two noisy signals to reduce the receiver noise

Answer: A

Diversity works only if the two branches are unlikely to be in a fade at the same moment, so the probability of an outage becomes the product rather than the sum of the individual probabilities. Space, frequency, angle, polarisation and route are simply different ways of obtaining that independence. Power doubling and noise averaging are different benefits, and selecting the better branch is one implementation among several. Independence, not duplication, is what buys the improvement.

Discuss in Forum

78.

What frequency range is normally used for terrestrial line of sight links?

A.Above one hundred gigahertz, where the antennas are smallest
B.About two to forty gigahertz
C.About one hundred to five hundred megahertz
D.About three to thirty megahertz in the high frequency bands

Answer: B

Fixed links occupy the bands from about two to forty gigahertz, with the lower bands used for long hops and the higher for short dense urban links. Below that the antennas would be unwieldy and the spectrum congested; above it, atmospheric absorption limits the range severely. High frequency bands are ionospheric rather than line of sight. Each part of the spectrum suits a range of hop lengths, and choosing the band is choosing the hop length.

Discuss in Forum

79.

Why are lower microwave bands used for longer hops?

A.The Fresnel zone is narrower at lower frequencies
B.Regulations reserve the lower bands for long distance links
C.Rain and gaseous attenuation are much smaller there
D.Antennas at lower frequencies have higher gain for a given size

Answer: C

Below about ten gigahertz rain is almost irrelevant and gaseous absorption negligible, so a modest fade margin covers a hop of tens of kilometres. Antenna gain for a given size falls rather than rises at lower frequency, the Fresnel zone is wider, and regulation follows physics. The two disadvantages are accepted because the atmospheric advantage dominates on a long path, which is a good example of one term in a budget outweighing several others.

Discuss in Forum

80.

Why are higher bands used for short urban links?

A.Rain attenuation is lower in cities than in open country
B.Buildings reflect higher frequencies more efficiently
C.Lower frequencies cannot carry the required data rates at all
D.Small antennas and wide bandwidth suit dense short hops

Answer: D

At thirty eight gigahertz a thirty centimetre dish gives high gain and narrow beams that allow dense reuse, and wide channels are available, which suits hops of a few kilometres between rooftops. Rain is a limitation rather than an advantage and is accepted because the hops are short. Building reflection is a nuisance, and lower bands can carry high rates given the spectrum. Matching the frequency to the hop length and the spectrum availability is the design decision.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: Space Wave Propagation Questions and Answers || Space Wave Propagation MCQ Questions and Answers || Space Wave Propagation GK Questions and Answers || Space Wave Propagation GK MCQ Questions || Space Wave Propagation Multiple Choice Questions and Answers || Space Wave Propagation GK || GK on Space Wave Propagation || Antenna and Wave Propagation Questions and Answers || Antenna and Wave Propagation MCQ Questions and Answers || Antenna and Wave Propagation GK Questions and Answers || GK on Antenna and Wave Propagation

Space Wave Propagation Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications