Space Wave Propagation Questions and Answers

Answer: C

A regenerative repeater recovers the data, removes accumulated noise and distortion and transmits a fresh signal, so impairments do not build up along a long chain. A non-regenerative repeater amplifies noise along with the signal, and the degradation accumulates hop by hop. Power supply arrangements and passive reflection are different matters. Restoring a signal to its ideal form at each stage is what allows a digital chain to be arbitrarily long, and it is the central advantage of digital transmission.

Answer: D

An analogue repeater cannot distinguish signal from noise, so it raises both and contributes its own noise figure, and the ratio degrades at every hop. Regeneration breaks the chain by making a decision and starting again. The signal is restored to level at each hop rather than weakening cumulatively, noise adds in power rather than coherently, and the atmospheric contribution is small at these frequencies. Whether impairments accumulate or are reset is the deciding difference between the two repeater types.

Answer: A

Hop length is set by line of sight geometry over the terrain and by the fade margin achievable at the chosen frequency, and the route is divided accordingly. Existing sites, capacity and spectrum influence the design but do not determine the hop count. In flat country hops of fifty kilometres are possible at lower microwave frequencies, while mountainous terrain may force much shorter ones. Geometry first, then margin, then everything else, is the order in which a route is planned.

Answer: B

Elevation extends the horizon and clears intervening terrain, so far fewer sites are needed than a route along a valley floor would require. The costs are access, power supply and exposure to weather and lightning. Rain attenuation is if anything similar, and a high site generally sees more interference rather than less, because it can see so far. Buying hop length with site difficulty is the classic trade in microwave route planning.

Answer: C

The same elevation that gives a long clear path to the next repeater also gives clear paths to every other transmitter within the extended horizon, so co-channel and adjacent channel interference must be assessed carefully at hilltop sites. Antenna directivity, atmospheric noise and pressure are not the mechanism. A property that helps the wanted signal helping the unwanted one equally is a recurring difficulty, and it is why frequency coordination is done site by site.

Answer: D

Before a link is licensed its potential to interfere with existing links, and their potential to interfere with it, is calculated from the geometry and the antenna patterns, and a frequency and polarisation are chosen to keep both within limits. Clock synchronisation, polarisation alignment and time sharing are different techniques. A shared resource allocated by calculation rather than by first come convention is what allows dense reuse of a fixed band.

Answer: A

Coordination depends on how little a link radiates and receives in directions other than its own, so the side lobe envelope, specified as a mask, decides how closely other links can operate. Forward gain matters for the link's own budget rather than for its neighbours. Bandwidth and weight are practical properties with no bearing on interference. A specification written in terms of what must not be radiated is what protects a shared band, exactly as it does for satellite earth stations.

Answer: B

A shrouded high performance dish radiates far less off boresight, so more links can share the band in the same area, which is precisely what a congested region needs. Its gain is similar to a standard dish of the same size, alignment becomes more rather than less critical, and robustness is incidental. Paying for a property that benefits everyone else in the band, rather than the link itself, is exactly the kind of externality that regulation exists to enforce.

Answer: C

A line of sight link succeeds or fails on the clearance of its Fresnel zone, the behaviour of the atmosphere over its route and the impairments the climate imposes, with power the least interesting variable. Free space loss is only the starting point of a budget. A generous margin helps but cannot substitute for correct geometry. Assessing the path before selecting the equipment is what distinguishes a designed link from an optimistic one.

Answer: D

The profile settles antenna heights, clearance, reflection points and hop feasibility before any equipment is chosen, and every later calculation refers back to it. Data sheets, licences and maintenance plans all follow from the design rather than driving it. Drawing the geometry first, and only then considering equipment and margins, is the order that avoids discovering an impossible path after the hardware has been bought.