MASI AC

In this question, the concepts of signal bandwidth (Bs), channel bandwidth (Bc) and center frequency (fc) are analyzed. The center frequency of a periodic square wave is inversely related to its period. The higher the center frequency is, the higher the bandwidth is. The bandwidth of a signal is related to the rate of changes in its parameters (amplitude, phase…). The center frequency of a transmitted signal must fall within the corresponding channel’s bandwidth.

The maximum bit-rate of ARINC-429 is 100 kbps. What would the maximum bit rate be of a modified ARINC-429 data bus if instead of binary symbols, a 128-level symbol alphabet was used?. 12.8 Mbps. 700 Kbps.

This question has to do with the source coding, and channel coding in digital communication systems: Source coding removes redundancy from the source data without any information loss. Channel coding always reduces the transmission bandwidth.

This question refers to analog and digital communication systems. Analog communication systems are unable to transmit digital information. Digital communication systems can transmit directly analog signals, without any modification or processing.

In this question, the concept of information is analyzed. Symbols that appear with low probability can be removed from a message because they do not carry considerable information. If we want to maximize the speed of transmission, it is convenient to increase the redundancy in the transmitted symbols. The most important symbols are those one which are the least probable. Predictable symbols can be left out and redundancy can be removed.

Consider a videoconference at 6 Mbps over a SatCOM data link operating at Ka-band (12 –18 GHz). Two modulation schemes are supported by the SatCOM transmitter: 4-PSK and 8-PSK. Assume that the transmitted bandwidth satisfies. The bandwidth occupied by the 8-PSK transmission is lower than that of the 4-PSK. The bandwidth occupied by the 4-PSK transmission is lower than that of the 8-PSK.

-90 dBm. -120 dBm. -78.5 dBm (-80 dBm aprox).

An engineer is designing a passband radio data link over a linear channel. The input data rate is 1 Mbps and the available bandwidth is 500 KHz. What modulation should s/he choose?. A M-FSK modulation, because it has a high bandwidth efficiency. A Binary PSK Modulation, because it is easier to demodulate. 16-QAM modulation.

What is the data encoding format and the maximum bit rate of an ARINC 429 data bus. 8PSK and 31.5 kbps. RZ Bipolar and 100Kbps=0.1 Mbps.

A small quadcopter is equipped with a 720p digital video camera. If you would like to download in real time the recorded video (FPV), which communication system would you select?. A 25-kHz digital datalink in the aeronautical VHF band. A 300MHz digital datalink in SHF band (5.8GHz).

This question refers to the noise effects on a radio system. The power of thermal noise increases with the center frequency. F bands are suitable for high-speed transmissions because there is almost no noise. In general, Signal-to-Noise Ratio increases with distance at frequencies above the VHF band. Thermal noise is predominant for fc > 100 MHz. The power of thermal noise increases (is proportional) with the bandwidth.

What is the primary source of noise in an airborne SatCOM receiver with its antenna connected?. Man-made noise. Galactic noise. Impulsive noise. Thermal Noise or Receiver front-end noise. fc for satcom is around 1.6 GHz, so primary source of noise is Thermal Noise.

What is the primary purpose of the first amplifier in a RF Front-End of a receiver?. To provide most of the receiver gain. To improve the receiver noise figure. To increase the power efficiency of the receiver. To reduce the noise along the receiver chain.

Which type of voice modulation is most often used for long distance voice communications on the HF bands, where ionospheric propagation is prevalent?. FM. AM. SSB.

A VHF Data Link (VDL) Mode 2 system is used to transmit data over 25 kHz channels within the 118 – 137 MHz band. The transmitted power is 10 W. The receiver sensitivity required for a Bit Error Rate of 10-3 is -75 dBm. Assuming Free-Space conditions for the propagation, and isotropic antennas, compute the maximum coverage area. At FL=300, around 270 NM (line-of-sight; 1 nautical mile: 1.852 m.). dmax = 30NM (1 nautical mile: 1.852m). dmax=53NM o 98km.

ICAO compliance requires a VDL receiver to provide a Bit Error Rate better than 10-2. If the Equivalent Thermal Noise Power at the receiver’s input is -95 dBm, compute the minimum received signal power: -80 dBW. 0.01 𝜇𝑊. -80 dBm. -110 dBW.

Orthogonal Frequency Division Modulation (OFDM), in contrast to conventional single carrier modulations like M-QAM or M-PSK, encodes data on multiple sub-carriers. Choose the correct answer(s). OFDM provides a flexible solution for frequency-dependent channels, because each sub- carrier can be independently modulated according to the channel’s behavior on the corresponding frequency. The extremely high complexity of OFDM has limited its real-world applicability. In fact, OFDM has been discarded in many actual communication systems, such as WIFI, 4G-LTE and in the future 5G systems, in which single-carrier modulations are preferred.

In radiolinks, which of the following factors increase the received power. To increase the frequency of the signal. To use antennas with high directivity. To increase the efficiency of the antennas. To use antennas with circular polarization.

The difference(s) between a waveguide and a transmission line is (are). The losses are much higher in waveguides. Both of them can support TEM modes. The power handling capability. Waveguides have cut-off frequency and transmission lines not.

A travelling plane wave. Cannot propagate inside a good conductor. Propagates in a direction parallel to Electric field. Has a propagation constant that defines the phase variation and attenuation with propagation. Propagates in an orthogonal direction to the electric field. Its frequency is constant. Its frequency changes with propagation.

What type of propagation involves radio signals that travel along and guided by the surface of the Earth?. Tropospheric diffraction. E-layer propagation. Sky-wave propagation. Space propagation. Ground –wave propagation.

What type of radio-wave propagation occurs when a signal travels from a transmitting antenna to a receiving antenna at microwave frequencies. Knife-edge diffraction. Duct propagation. Straight line propagation. Tunnel Propagation. Line of sight. Direct Wave.

When a wave is propagating in free space and find an obstacle in its way. There is always reflection and consequently standing waves appear. There may be Reflection, Diffraction, Scattering, Absorption or any combination.

What path do radio waves usually follow from a transmitting antenna to a receiving antenna at VHF or higher frequencies?. A bent path through the ionosphere. A great circle path parallel to the surface of the earth. A ground wave. A straight-line. A slightly bent path.

The antennas for a given service in the airplane. Must always have circular polarization because of the atmosphere. The type of antenna to use for a given application depends on the frequency, type of application, where it has to be located, etc. Depends on the frequency, type of application, where is located. Radiation Pattern gives the most relevant information and can be easily tailored if we can use arrays.

In a satellite communication service in an airplane. The different layers of the atmosphere have different effects at different frequencies. The delay in receiving the signal is higher at higher frequencies. The delay in receiving the signal is the same for all frequencies.

Will SATCOM systems replace HF systems for long range communications?. Yes because SATCOM communications are more reliable. No, they will be used at least to increase the redundancy.

The mechanism(s) used to transmit data from a single source to a single destination is (are). Broadcast. Unicast. Multicast.

The topology where all devices are connected through a single network hub is. Mesh. Star. Ring. Bus.

Flow control is a technique used. To detect errors. To detect collisions. To assure that a transmitting entity does not overwhelm a receiving entity with data.

In connectionless packet switching. At least one packet has errors during the transmission. Signal goes out automatically without determining whether the receiver is ready, or even whether a receiver exists. Segments (data packets) are not acknowledged at reception. The loss of a segment will not be detected by connection-less protocols.

A spanning tree. Is used to maximize the efficiency between hosts. Is used to have leafs in computer networks. Is used to have roots in computer networks. Is used to avoid loops. generates a logic topology on top of the physical one.

Which one is NOT a medium access technique. Aloha. CSMA/CA. (está utilizada para cuando el medio es el aire). TDM, FDM.

Which service is NOT provided by the IP Protocol?. Fragmentation. Addressing for private use. Quality of service.

This question refers to different concepts related to speech technologies. Speech signals only contain information about the linguistic message. Speech signals can convey information about the emotional status of the speaker.

This question refers to automatic speech recognition and text-to-speech systems. The performance of a speaker verification system depends on the number of speakers registered. In text-to-speech systems, it is only necessary to synthesize the suprasegmental characteristics (prosody) of speech. The dictionary or vocabulary of a speech recognition system contains the lists of words that can be recognized. State-of-the art text-to-speech systems are based on deep learning techniques. in continuous speech recognition systems, the user should introduce pauses between words. In isolated Speech recognition systems, the user should introduce pauses between words. In Continuous speech recognition systems, the user does not need to introduce pauses between words. In text-to speech systems, it is necessary to synthesize the segmental characteristics AND the suprasegmental characteristics (which are harder).