Explanation:
A digital signal is one in which the original information is converted into a string of bits before being transmitted.
A radio signal, for example, will be either on or off. Digital signals can be sent for long distances and suffer less interference than Analog signals. The communications industry worldwide is in the midst of a switch to digital signals. Sound storage in a compact disk is in digital form. This type of signal is transmitted on the internal bus structure of the motherboard and processor or across a network. It represents the binary value of the transmitted data. The signal pattern of the data consists of a series of high and low frequencies.A simplified depiction of a digital signal is shown in the below figure.
Answer option D is incorrect. An Analog or analogue signal is any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are meaningful. Analog is usually thought of in an electrical context; however mechanical, pneumatic, hydraulic, and other systems may also convey analog signals.An analog signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses rotary position as the signal to convey pressure information. Electrically, the property most commonly used is voltage followed closely by frequency, current, and charge.For example, in sound recording, fluctuations in air pressure (that is to say, sound) strike the diaphragm of a microphone which induces corresponding fluctuations in the current produced by a coil in an electromagnetic microphone, or the voltage produced by a condenser microphone. The voltage or the current is said to be an 'analog' of the sound.
A simplified depiction of analog signal is shown in the figure below.
Answer option B is incorrect.
A carrier signal is a transmitted electromagnetic pulse or wave at a steady base frequency of alternation on which information can be imposed by increasing signal strength, varying the base frequency, varying the wave phase, or other means. This variation is called modulation. With the advent of laser transmission over optical fiber media, a carrier can also be a laser-generated light beam on which information is imposed.Types of analog modulation of a carrier include amplitude modulation (AM), frequency modulation (FM), and phase modulation. Types of digital modulation include varieties of pulse code modulation (PCM), including pulse amplitude modulation (PAM), pulse duration modulation (PDM), and pulse position modulation (PPM).
Answer option C is incorrect. An off-hook signal is an informational signal generated by analog phones.
A receiver off-hook signal is used to indicate that a telephone receiver is placed off- hook and there is no activity on that line. Since an analog phone considers dialing to be the only detectable "activity", a voice dialog between a caller and a voice recognition system does not normally disengage the connection.