Avionics Mcqs - Set 10

ANSWER: Fast microprocessors

Explanation:
Since in undersampling the time period between samples is sufficiently large, this allows slower processors to be used for ADC. This also allows low memory capacity for storage and less power consumption.

ANSWER: Flash conversion

Explanation:
R-2R, string and weighted current source converters are Digital to analog conversion methods whereas flash conversion is an analog to digital conversion method. Flash converter uses a voltage ladder along with a comparator to compare the reference voltage with the input voltages.

ANSWER: Input amplifiers

Explanation:
The R-2R Digital to analog converter consists of four major parts. They are Reference regulators, Resistor network, Electronic switches, and output amplifiers. An output amplifier is used to scale the output voltage of the signal to any desired level.

ANSWER: 1.25V

Explanation:
No explanation is available for this question!

ANSWER: 13MHz

Explanation:
Frequency of alias signal = fa = fs – fm = 28-15 = 13MHz.

ANSWER: False

Explanation:
Settling time is the amount of time it takes for the output voltage of a DAC, after a change in binary input, to stabilize to within a specific voltage range. The output is thus not an accurate representation of the binary input; it is not usable until it settles down.

ANSWER: 10MHz

Explanation:
Operational frequency = 1 / (100 x 10-9)= 10MHz. Operational frequencies higher than this would produce errors.

ANSWER: True

Explanation:
During its sampling mode, a sample-and-hold (S/H) circuit accepts the analog signal and passes it unchanged. In the hold mode, the amplifier remembers a particular voltage level at the instant of sampling.

ANSWER: Flash conversion

Explanation:
The flash converter produces an output as fast as the comparators can switch and the signals can be translated to binary levels by the logic circuits. Comparator switching and logic propagation delays are extremely short. Thus, flash converters are the fastest type of A/D converter.

ANSWER: 732.5μV

Explanation:
No explanation is available for this question!

ANSWER: 72.24dB

Explanation:
No explanation is available for this question!

ANSWER: Pulse modulation

Explanation:
In pulse modulation, the information to be transmitted is represented by a series of binary pulses. Since the pulse information is binary in nature analog signal shave to be converted to digital before transmitting.

ANSWER: Can transmit analog as well as digital waves

Explanation:
Analog values cannot be transmitted as such by pulse modulation since it can only transmit binary data. However, the analog signal can be converted into digital using an ADC and then transmitted via pulse modulation.

ANSWER: Pulse frequency modulation

Explanation:
There are four basic forms of pulse modulation. They are: pulse amplitude modulation, pulse width modulation, pulse position modulation pulse code modulation. In any form of pulse modulation, the frequency of the signal is not changed.

ANSWER: 2

Explanation:
The amplitude of PWM is binary in nature meaning that it has only two levels. The amplitude of the modulating signals varies the width of the pulses generated.

ANSWER: True

Explanation:
In pulse modulation, the carrier is not transmitted continuously but in pulses whose width is determined by the amplitude of the modulating signal. The duty cycle is made in such a way that the carrier is off for a longer time than it bursts hence the average power consumption is low.

ANSWER: Pulse amplitude modulation

Explanation:
Out of all the pulse modulation techniques, Pulse amplitude modulation is the least expensive and simplest to implement. In pulse amplitude modulation, the amplitude of the pulse varies with the amplitude of the modulating signal.

ANSWER: Pulse width changes in accordance with the amplitude of modulating signal

Explanation:
In PPM, the pulses change position according to the amplitude of the analog signal. The pulses are very narrow. These pulse signals may be transmitted in a baseband form, but in most applications, they modulate a high-frequency radio carrier.

ANSWER: Communication of airplane with ATC

Explanation:
Pulse modulation is used in telemetry systems to monitor spacecraft or missile, RC models, for switching power supplies like regulators and also as audio switching power amplifiers. Communication of airplane with ATC is amplitude modulated waves.

ANSWER: Companding

Explanation:
To reduce the effects of noise and distortion in pulse modulation, a process called companding is done. Companding is a process of signal compression and expansion.

ANSWER: Pulse code modulation

Explanation:
The most widely used technique for digitizing information signals for electronic data transmission is pulse code modulation. It has uniform transmission quality and also can be used when the signal traffic is high.

ANSWER: 0.75V

Explanation:
No explanation is available for this question!

ANSWER: 1.02V

Explanation:
No explanation is available for this question!

ANSWER: True

Explanation:
DSP is the use of a fast digital computer or digital circuitry to perform processing on digital signals. Any digital computer with sufficient speed and memory can be used for DSP.

ANSWER: Stored in a RAM

Explanation:
When the signal is converted from analog to digital it is a sequence of binary numbers which is stored in the RAM. A user defined code that is usually stored in the ROM performs mathematical and other manipulations after which it is converted back into analog signals.

ANSWER: John Von Neumann

Explanation:
Physicist John Von Neumann is generally credited with creating the stored program concept that is the basis of operation of all digital computers. Binary words representing computer instructions are stored sequentially in a memory to form a program. The instructions are fetched and executed one at a time at high speed.

ANSWER: Von Neumann bottleneck

Explanation:
The accessibility limitation of only one data or instruction set at a time from the memory is called as Von Neumann bottleneck. This has the effect of greatly limiting the execution speed.

ANSWER: Harvard architecture

Explanation:
In a Harvard architecture microprocessor, there are two memories, a program or instruction memory, usually a ROM, and a data memory, which is a RAM. Also, there are two data paths into and out of the CPU between the memories. Because both instructions and data can be accessed simultaneously, very high-speed operation is possible.

ANSWER: High sampling frequency

Explanation:
The time taken for input/output and the processing time together must be smaller than the sampling period to ensure the continuous flow of data. Since high sampling frequencies are needed for accurately converting the analog signal to digital, high speed DSP is a must.

ANSWER: True

Explanation:
With DSP, the filters can have characteristics far superior to those of equivalent analog filters. Selectivity can be better because of the ease of controlling binary numbers, and the passband or reject band can be customized to the application.

ANSWER: Data compression

Explanation:
Data compression is a process that reduces the number of binary words needed to represent a given analog signal. Since analog to digital conversion produces a huge amount of data, for transmission it is a necessity that data is compressed.

ANSWER: Spectrum analysis

Explanation:
Spectrum analysis is the process of examining a signal to determine its frequency content. Algorithms such as discrete Fourier transform (DFT) and FPGA is used to analyze the frequency content of an input signal.

ANSWER: Fast Fourier transforms

Explanation:
The DFT is a complex program that is long and time-consuming to run. In general, computers are not fast enough to perform DFT in real time as the signal occurs. Therefore, a special version of the algorithm has been developed to speed up the calculation. Known as the fast Fourier transform (FFT), it permits real-time signal spectrum analysis.

ANSWER: Data compression

Explanation:
Data compression is done by checking redundancy in data. Data redundancy checking is only possible when the data is in digital form and hence data compression cannot be done in analog signals.

ANSWER: Continuous wave transmission

Explanation:
The oscillator generates the carrier and can be switched off and on by a telegraph key to produce the dots and dashes of the International Morse code. Information transmitted in this way is referred to as continuous-wave (CW) transmission. Such a transmitter is rarely used today.

ANSWER: Duplexer

Explanation:
A duplexer is a device that is placed just before the antenna in a transducer system. It is basically a switch which allows both transmission and reception but only one at a time.

ANSWER: Oscillator

Explanation:
An oscillator, in most applications a crystal oscillator, generates the final carrier frequency. A modulator simply adds the information signal and an antenna transmits the signal.

ANSWER: True

Explanation:
The frequency multiplier increase the carrier frequency to the desired output frequency, but also it multiplies the frequency deviation produced by the modulator. The design of the transmitter must be such that the frequency multipliers will provide the correct amount of multiplication not only for the carrier frequency but also for the modulation deviation.

ANSWER: Variable frequency oscillator

Explanation:
A variable frequency oscillator (VFO) is used to provide continuous tuning over a desired range. Using VFO different carrier frequencies can be generated.

ANSWER: Crystal Oscillator

Explanation:
The transmitter must remain on the assigned frequency. It must not drift off or wander from its assigned value despite the many operating conditions, such as wide temperature variations and changes in power supply voltage, that affect frequency. The only oscillator capable of meeting the precision and stability demanded by the FCC is a crystal oscillator.