Avionics MCQs – Time Division Multiplexing

1 - Question

Frequency division multiplexing:Frequency slots::time division multiplexing:?
a) Time slots
b) Coded information
c) Pulsed information
d) Band slots
View Answer Answer: a
Explanation: In FDM, multiple signals are transmitted over a single channel, each signal being allocated a portion of the spectrum within that bandwidth. In time-division multiplexing (TDM), each signal occupies the entire bandwidth of the channel. However, each signal is transmitted for only a brief time. In other words, multiple signals take turns transmitting over the single channel.

2 - Question

Serial transmission is not possible without time division multiplexing.
a) True
b) False
View Answer Answer: a
Explanation: In serial transmission, the data is sent via a single cable. When a clock pulse is applied to the shift register it transmits the information bit by bit in allocated time slots.

3 - Question

What device is used to demodulate a time division multiplexed analog wave?
a) High pass filter
b) Low pass filter
c) Band stop filter
d) Attenuator
View Answer Answer: b
Explanation: the analog signal is converted to a series of constant-width pulses whose amplitude follows the shape of the analog signal. The original analog signal is recovered by passing it through a low-pass filter. In TDM using PAM, a circuit called a multiplexer (MUX or MPX) samples multiple analog signal sources; the resulting pulses are interleaved and then transmitted over a single channel.

4 - Question

Which of the following device was used in early TDM/PAM telemetry systems?
a) Commuter
b) Linear switch
c) Logic gates
d) DSP
View Answer Answer: a
Explanation: Multiplexers in early TDM/PAM telemetry systems used a form of rotary switch known as a commutator. Multiple switch segments were attached to the various incoming signals while a high-speed brush rotated by a dc motor rapidly sampled the signals as it passed over the contacts.

5 - Question

What is the time allocated for each channel if the number of samples per frame is 4 and the frame rate is 100frames/sec?
a) 1.2ms
b) 3ms
c) 2.5ms
d) 0.54ms
View Answer Answer: c
Explanation: Time period for one frame = 1/100 = 0.01s = 10ms. During that 10-ms frame period, each of the four channels is sampled once. Each channel is thus allotted 10/4 = 2.5 ms.

6 - Question

What is the purpose of one shot multivibrator?
a) Trigger all AND gates at clock frequency
b) Trigger all OR gates at clock frequency
c) Trigger all AND gates at signal frequency
d) Trigger all OR gates at signal frequency
View Answer Answer: a
Explanation: The one-shot multivibrator is used to trigger all the decoder AND gates at the clock frequency. It produces an output pulse whose duration has been set to the desired sampling interval.

7 - Question

The circuit used to regenerate clock pulses from the transmitted PAM signals is called ____
a) Clock demodulator circuits
b) Timer circuits
c) Clock receiving circuits
d) Clock recovery circuits
View Answer Answer: d
Explanation: Instead of using a free-running clock oscillator set to the identical frequency of the transmitter system clock, the clock for the demultiplexer is derived from the received PAM signal itself. A circuit called the clock recovery circuits are typical of those used to generate the demultiplexer clock pulses.

8 - Question

What are used to reduce or stop synchronization problems while receiving?
a) Clock recovery circuits
b) Demodulators
c) Synchronizer
d) Band pass filter
View Answer Answer: a
Explanation: Clock recovery circuits are used to remedy the synchronization problem encountered in demultiplexing. The clock pulse is derived from the transmitted signal so that synchronization errors are reduced.

9 - Question

In a four channel system, all four signals transmitted contain information.
a) True
b) False
View Answer Answer: b
Explanation: After clock pulses of the proper frequency have been obtained, it is necessary to synchronize the multiplexed channels. This is usually done with a special synchronizing (sync) pulse applied to one of the input channels at the transmitter. In the four-channel system discussed previously, only three actual signals are transmitted. The fourth channel is used to transmit a special pulse whose characteristics are unique in some way so that it can be easily recognized.

10 - Question

Which of the following is not an advantage of time division multiplexing?
a) Signal interference is less
b) More flexible
c) Full channel can be used for every signal
d) Fast data transfer
View Answer Answer: d
Explanation: Since the time available for transmission is shared by all the signals that are modulated, Time division multiplexing is not fast when compared with other multiplexing techniques. However, for applications such as telemetry, with a high sampling rate, the speed of time division multiplexing is sufficient to meet the requirements.

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