Space Wave Propagation Questions and Answers

Q: What is the consequence of moving a broadcast service to a higher frequency band?

Greater diffraction and clutter loss shrink the area a single site can serve, so a network that used a handful of high power stations may need hundreds of smaller ones. The additional antenna gain available at higher frequency does not compensate for the terrain and clutter losses. It is why spectrum below one gigahertz is so valuable for wide area services, and why its reallocation is contested. A propagation property translating directly into infrastructure cost is what makes spectrum policy an economic question.

Q: What is line of sight propagation?

A line of sight path is one in which the direct ray, with adequate Fresnel clearance, reaches the receiver without obstruction, and it is the basis of microwave links, satellite paths and most mobile coverage near a base station. Surface guidance, ionospheric return and scatter are separate mechanisms with their own bands and behaviours. Establishing which mechanism applies before predicting anything is the first step in every propagation problem.

Q: What limits the range of a line of sight link over flat ground?

The horizon distance follows from the antenna heights and the effective earth radius, and beyond it the path is obstructed by the earth itself whatever the power. Raising the antennas is the only geometric remedy. Power affects the margin rather than the geometry, bandwidth affects the noise, and ground conductivity governs the surface wave rather than this mechanism. A limit set by geometry cannot be overcome by improving the equipment.

Q: Why are microwave link antennas mounted on towers?

Raising the antennas pushes the horizon further and lifts the beam clear of buildings and trees so that the Fresnel zone is unobstructed, which is usually the dominant consideration in siting. Interference and safety are secondary benefits, and antenna gain is a property of the structure rather than of its height. The height of a tower is bought to satisfy a geometric requirement, and calculating that requirement precisely is what a path profile is for.

Q: What happens to a link if a new building is erected in the Fresnel zone?

Any intrusion into the first Fresnel zone removes part of the contributing wavefront, so loss appears even while the direct ray remains geometrically clear, and the margin that was protecting the link against rain is consumed by a permanent term. Planning consultation over microwave paths exists for this reason. Reflection can occur too but does not compensate, and polarisation is unaffected. A permanent loss eating a margin intended for a varying one is a particularly damaging kind of degradation.

Q: Why is a link's fade margin not a defence against a permanent obstruction?

A margin is calculated so that time varying fades exceed it only for the permitted outage period, and a constant loss simply reduces the whole budget, leaving less to absorb those fades. The correct treatment is to include the obstruction as a fixed loss and recompute the margin. Frequency, seasonal applicability and alignment are unrelated. Distinguishing a constant term from a statistical one determines where in a budget it belongs and how it must be covered.

Q: What is the effect of raising both antennas on a line of sight path?

Additional height pushes the horizon further and lifts the ray away from obstacles, improving clearance and often removing a ground reflection. Free space loss depends on distance rather than height, so it does not fall, and rain and frequency are unaffected. The two ray height gain that applies to low mobile antennas is a different regime. Knowing which regime a path is in decides whether height buys signal or merely clearance.

Q: Why does the two ray height gain not apply to a well cleared microwave link?

The height gain arises from the near cancellation of a strong reflected ray, and a link designed to avoid that reflection is left with the direct ray alone and free space loss. Antenna directivity helps by discriminating against the reflection, which is part of good design rather than an automatic property. The ground does reflect at microwave frequencies, and the reflected ray reaches the receiver readily on a flat path. A model applies only where its assumptions hold, and here they have been deliberately broken.

Q: What is a repeater on a microwave route?

An active repeater receives on one frequency, amplifies or regenerates the signal and retransmits it on another towards the next site, breaking a long route into hops each within line of sight. Passive reflectors achieve a change of direction without electronics, and filters and dual beam antennas are components rather than stations. Chaining short hops to cross a long distance is what makes terrestrial microwave routes possible over any terrain.

Q: Why does a repeater transmit on a different frequency from the one it receives?

With the transmitter and receiver on the same tower, even sixty or eighty decibels of antenna isolation would not prevent oscillation if both used the same frequency, so a frequency pair is used and the roles alternate along the route. Regulation follows the technical need, amplification efficiency is unaffected, and antennas handle multiple signals routinely. Positive feedback around a loop with gain is the risk being avoided, and the same argument governs any repeater in any medium.

81.

What is the consequence of moving a broadcast service to a higher frequency band?

A.Many more transmitter sites are needed for the same coverage
B.The same coverage is achieved with a proportionally lower power
C.Coverage improves because antenna gain rises with frequency
D.Coverage is unaffected provided the radiated power is unchanged

Answer: A

Greater diffraction and clutter loss shrink the area a single site can serve, so a network that used a handful of high power stations may need hundreds of smaller ones. The additional antenna gain available at higher frequency does not compensate for the terrain and clutter losses. It is why spectrum below one gigahertz is so valuable for wide area services, and why its reallocation is contested. A propagation property translating directly into infrastructure cost is what makes spectrum policy an economic question.

Discuss in Forum

82.

What is line of sight propagation?

A.Propagation by scattering from turbulence in the troposphere
B.Propagation along a clear direct path between two antennas
C.Propagation guided along the surface of the earth between them
D.Propagation returned to earth by the ionised upper atmosphere

Answer: B

A line of sight path is one in which the direct ray, with adequate Fresnel clearance, reaches the receiver without obstruction, and it is the basis of microwave links, satellite paths and most mobile coverage near a base station. Surface guidance, ionospheric return and scatter are separate mechanisms with their own bands and behaviours. Establishing which mechanism applies before predicting anything is the first step in every propagation problem.

Discuss in Forum

83.

What limits the range of a line of sight link over flat ground?

A.The bandwidth of the modulation being transmitted
B.The conductivity of the ground between the two antennas
C.The curvature of the earth and the antenna heights
D.The transmitter power available at the sending station

Answer: C

The horizon distance follows from the antenna heights and the effective earth radius, and beyond it the path is obstructed by the earth itself whatever the power. Raising the antennas is the only geometric remedy. Power affects the margin rather than the geometry, bandwidth affects the noise, and ground conductivity governs the surface wave rather than this mechanism. A limit set by geometry cannot be overcome by improving the equipment.

Discuss in Forum

84.

Why are microwave link antennas mounted on towers?

A.Towers reduce the interference from other users nearby
B.Elevation improves the antenna's efficiency and gain
C.The equipment must be kept away from people for safety
D.Height extends the horizon and clears local obstacles

Answer: D

Raising the antennas pushes the horizon further and lifts the beam clear of buildings and trees so that the Fresnel zone is unobstructed, which is usually the dominant consideration in siting. Interference and safety are secondary benefits, and antenna gain is a property of the structure rather than of its height. The height of a tower is bought to satisfy a geometric requirement, and calculating that requirement precisely is what a path profile is for.

Discuss in Forum

85.

What happens to a link if a new building is erected in the Fresnel zone?

A.Diffraction loss appears and the fade margin is reduced
B.The link is unaffected as long as the direct ray is still clear
C.The building reflects the signal and improves the received level
D.The polarisation is rotated and the receiver loses lock entirely

Answer: A

Any intrusion into the first Fresnel zone removes part of the contributing wavefront, so loss appears even while the direct ray remains geometrically clear, and the margin that was protecting the link against rain is consumed by a permanent term. Planning consultation over microwave paths exists for this reason. Reflection can occur too but does not compensate, and polarisation is unaffected. A permanent loss eating a margin intended for a varying one is a particularly damaging kind of degradation.

Discuss in Forum

86.

Why is a link's fade margin not a defence against a permanent obstruction?

A.The obstruction affects the antenna alignment rather than the path
B.It is sized for varying impairments and is consumed by a fixed loss
C.A permanent obstruction changes the frequency of the link
D.Margins apply only during rain and not at other times

Answer: B

A margin is calculated so that time varying fades exceed it only for the permitted outage period, and a constant loss simply reduces the whole budget, leaving less to absorb those fades. The correct treatment is to include the obstruction as a fixed loss and recompute the margin. Frequency, seasonal applicability and alignment are unrelated. Distinguishing a constant term from a statistical one determines where in a budget it belongs and how it must be covered.

Discuss in Forum

87.

What is the effect of raising both antennas on a line of sight path?

A.The frequency at which the link operates may be raised
B.The rain attenuation on the path is reduced significantly
C.The horizon extends and the clearance improves
D.The path loss falls in proportion to the height increase

Answer: C

Additional height pushes the horizon further and lifts the ray away from obstacles, improving clearance and often removing a ground reflection. Free space loss depends on distance rather than height, so it does not fall, and rain and frequency are unaffected. The two ray height gain that applies to low mobile antennas is a different regime. Knowing which regime a path is in decides whether height buys signal or merely clearance.

Discuss in Forum

88.

Why does the two ray height gain not apply to a well cleared microwave link?

A.The antennas are too directive to receive any reflected signal
B.The frequency is too high for the ground to reflect at all
C.The path is too long for the reflected ray to reach the receiver
D.A properly sited link has no strong ground reflection to interfere

Answer: D

The height gain arises from the near cancellation of a strong reflected ray, and a link designed to avoid that reflection is left with the direct ray alone and free space loss. Antenna directivity helps by discriminating against the reflection, which is part of good design rather than an automatic property. The ground does reflect at microwave frequencies, and the reflected ray reaches the receiver readily on a flat path. A model applies only where its assumptions hold, and here they have been deliberately broken.

Discuss in Forum

89.

What is a repeater on a microwave route?

A.A station that receives, amplifies and retransmits the signal
B.A device that reflects the beam without any electronics
C.An antenna that radiates in two directions simultaneously
D.A filter that removes interference from the received signal

Answer: A

An active repeater receives on one frequency, amplifies or regenerates the signal and retransmits it on another towards the next site, breaking a long route into hops each within line of sight. Passive reflectors achieve a change of direction without electronics, and filters and dual beam antennas are components rather than stations. Chaining short hops to cross a long distance is what makes terrestrial microwave routes possible over any terrain.

Discuss in Forum

90.

Why does a repeater transmit on a different frequency from the one it receives?

A.Because the antenna cannot handle two signals at one frequency
B.To prevent the transmitter from feeding back into its own receiver
C.Because the regulator allocates a separate frequency to each hop
D.To allow the signal to be amplified more efficiently

Answer: B

With the transmitter and receiver on the same tower, even sixty or eighty decibels of antenna isolation would not prevent oscillation if both used the same frequency, so a frequency pair is used and the roles alternate along the route. Regulation follows the technical need, amplification efficiency is unaffected, and antennas handle multiple signals routinely. Positive feedback around a loop with gain is the risk being avoided, and the same argument governs any repeater in any medium.

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