for general telecommunication and surveillance, spot beams are used for magnified views of the Earth and are ideal for targeting purposes and close-up surveillance of specific areas. Spot beams are also used in telecommunications for direct links between a specific satellite and a specific transponder.

How Spot Beam Works

A spot beam is produced in the same way that a broad beam is, but is focused at a specific area of the Earth’s surface. A spot beam begins as an electrical signal that is converted into a radio frequency by means of a dipole, which is simply two intersecting antennas that vibrate when a current is passed through it. This vibration produces a radio frequency that can then be focused with the aid of a cone or dish. While a broad beam is produced by a dish that is focused outward, a spot beam is produced by a dish that is angled inward.

Applications

Spot beams are used for a wide variety of applications, such as unit-specific GPS navigation and satellite-to-ground synchronization as well as regular uplinks and downlinks between a satellite and a specific transponder. While some satellites are able to change the angle of their dish in order to create both spot beams and broad beams, most satellites are only capable of producing one or the other.

Advantages

Spot beams are advantageous because they allow orbital satellites to target a specific ground-based unit. This limits the opportunity for third-party systems to intercept the data and minimizes the amount of power that is necessary to transmit the data.

Vocabulary:

spot beam – сфокусированный луч broad beams – широкий пучок dipole – дипольный

intersecting antennas – пересекающиеся антенны

uplinks and downlinks – восходящие и нисходящие ссылки intercept – перехват, остановка

Transponder

A transponder is an automatic electronic monitoring or control device that receives, cross-examines, amplifies and retransmits the arriving signal. It is primarily implemented in wireless communication. The word ‘Transponder’ itself is a combination of two words; transmitter and responder (occasionally abbreviated to TPDR, TR, XPNDR, and XPDR).

A transponder works by receiving a signal on a component called “interrogator” since it effectively inquires for information, then automatically transmitting a radio wave

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signal at a predestined frequency. In order to broadcast a signal on a dissimilar frequency than the one received, a special component called the “frequency converter” is provided. By receiving and transmitting on dissimilar frequencies, the interrogator and transponder signals can be sensed concurrently.

Transponder is also principally used as a re-transmitter due to the fact that it receives a definite signal from a specific source, then it amplifies (magnifies) the signal before sending it to a predefined location. Transponders have an abnormally large number of applications in various fields; satellite communication, aviation, marine, automotive, road, motorsport, underwater etc. They are also used in simple day-to-day tasks such as opening a car’s door wirelessly. The earliest implementation of a transponder was aboard an airplane during World War II, as component of the Identify Friend or Foe (IFF) system. By responding undisclosed interrogation frequencies, the airplane pilots could point out to radar operators that they were friendly airplanes. Transponders are also used to compute distance by evaluating the elapsed time between the transferring of a signal and acknowledgment of the transponder’s signal. For example, sonar transponders are used to locate undersea places, estimate depth, and trace locations.

Transponders are basically of two types; active transponders and passive transponders.

Active Transponders

As the name suggests, these devices constantly emit radio signals which are tracked and monitored. These can also be automatic devices which strengthen the received signals and relay them to another location.

An active transponder includes its very own power supply. The active transponder will constantly “ping” its recognition from time to time and the reader will listen for any transponders in the area. If the active transponder pings very frequently it will be detected quickly. Frequent pinging will eventually consume more power. If the transponder pings occasionally there will be a little postponement until it is detected, however the power will last longer.

The benefit of an active transponder is that it possesses comparatively longer range. Sometime, this characteristic could also be a setback if the range is too big. The shortcoming of an active transponder is that they are bulky, expensive and have a comparatively short power life.

These devices are so commonly used that we often fail to recognize them. For example, how do you think lap times of NASCAR and Formula One cars are monitored so accurately? The answer lies in the transponders which are embedded into the cars. Each car has a unique ID code which is transmitted as the car travels. A special cable loop is dug into the ground at the start and finish lines. When the cars zoom by the finish line, their IDs are recorded along with their lap times. These recorded times are automatically displayed on the position board along with split times, laps remaining and so on.

Another significant implementation of active transponders is in satellite communications. Generally there are hundreds of thousands of tiny transponders embedded in a single satellite. These transponders receive an incoming signal over a range of frequencies (band), measured in Hertz and Megahertz and retransmit these signals on a different band concurrently. The incoming signal originating from a location on the

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earth (e.g. a broadcaster), is called the uplink and the outgoing signal back to the earth is called the downlink. The logic behind using satellites for this purpose is simple – as radio signals cannot curve along the curvature of the earth, they are sent in a straight line up and received down in a straight line. This reduces time of signal delivery and increases range.

Passive Transponders

A passive transponder does not include its own power source. The passive transponder collects power from a close by electric or magnetic field offered by a reader. The reader cross-examines the neighboring field for transponders that may be in its proximity and stimulates enough power into the transponder’s electronic circuitry that the transponder becomes active and retransmits to the reader its identification ID as well as any added information required.

The benefit of a passive transponder is that they are reasonably priced, small and they practically do not need a power change. The shortcoming of a passive transponder is that they have comparatively restricted range. It is perfect for an identification label that will be examined at close proximity.

These transponders hold information which is used to identify particular objects. For example, passive transponders are sometimes embedded into our credit cards and on magnetic labels in large stores. These are paired with active transponders which amplify and transcribe the information.

Vocabulary:

transponder – ретранслятор interrogator – устройство опрашивания

predestined frequency – предопределенная частота dissimilar frequency – разнородные частоты concurrently – одновременно

predefined location – определенное положение implementation – реализация, выполнение, осуществление a little postponement – небольшая отсрочка

embedded – встроенный cable loop – кабельная петля

shortcoming – недостаток, дефект

proximity – приближение, сближение; бесконтактный frequent pinging – частый тестовый опрос postponement – отсрочка, задержка

BUC

A BUC (Block Upconverter) is a device that converts radio signals from a lower frequency to a higher frequency. BUCs are used in satellite uplink transmissions in order to transfer data from a ground based unit to a satellite in orbit that will then be re-

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directed to another ground based unit in separate location. Likewise, BUCs are used in long distance communication between two or more ground based radio towers. BUCs are often found in communication broadcast systems for television and Internet access, weather systems, and government agencies.

How a BUC Works

A BUC converts bands of low digital frequencies that represent data into bands of high radio frequencies that can travel much farther into space in order to reach satellites and other spacecraft that are in the Earth’s orbit. Each frequency is used as a form of Morse Code in which data is translated back and forth between radio waves and digital information. Each band represents a collection of frequencies in order to distinguish each set of data.

Band Comparisons

Typical BUCs convert frequencies from the L band to the Ku, Ka, and C bands. The L band refers to four separate bands of electromagnetic waves including 40 – 60 Ghz (for tracking), 1 – 2 Ghz (for communication), 1565 nm – 1625 nm (for optical applications), and 3.5 micrometers (for infrared astronomy). The Ku (K-under) and Ka (K- above) refer to the portion of microwaves directly under and above the K band respectively, which are both typically used for radar. The C-band refers to several points of microwaves in the electromagnetic spectrum that are used for long distance communication, which is the type that television and Internet broadcasting systems most commonly use.

Frequency Comparisons

An oscillator, which is a device that is capable of producing harmonics depending on how much electricity is passed through it, generates frequencies. Because oscillators can produce the same harmonics repeatedly, time can be used to derive a pattern from a frequency and translate it into data. However, because electromagnetic waves tend to fade with distance, a signal’s frequency must be repeated much faster in long distance applications in order to reach targets that are farther away. Frequencies that are repeated many times in a short amount of time are referred to as “high frequencies,” while frequencies that are repeated less times in the same amount of time are referred to as “low frequencies.” Low frequencies are still useful, but are reserved for close range communication or telemetry between two objects.

Vocabulary:

BUC (Block Upconverter) – блок преобразователя digital frequencies – цифровые частоты

infrared astronomy – инфракрасная астрономия oscillator – излучатель, генератор

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