Quiz 6

A binary PCM system with 256 quantizing levels has a sampling frequency of 7 kHz. The bit rate of the system is

• 56 kbps

• 28 kbps

• 1792 kbps

• 896 kbps

A sinusoidal message signal is being transmitted by an 8-bit binary PCM. If the bits/codeword is reduced by a factor of 2, the output signal-to-quantization noise ratio will

• reduce by 3 dB

• reduce by 12 dB

• reduce by 6 dB

• reduce by 24 dB

In binary PCM, the SNR

• increases linearly with the number of bits/codeword

• increases as the square of the number of bits/codeword

• does not depend upon the number of bits/codeword

• increases exponentially with the number of bits/codeword

In a binary PCM system, the output signal-to-quantizing noise ratio is to be held to a minimum value of 40 dB. The number of required levels are

• 5

• 6

• 7

• 8

The line code which suppresses the dc component is

• bipolar return-to-zero code

• Manchester code

• polar non-return-to-zero code

• unipolar non-return-to-zero code

The line code which permits bit-timing recovery at the receiver, is

• bipolar return-to-zero code

• Manchester code

• polar non-return-to-zero code

• unipolar non-return-to-zero code

The line code which has an inbuilt error-detecting capability against sign inversion of transmitted pulse due to

channel noise, is

• bipolar return-to-zero code

• Manchester code

• polar non-return-to-zero code

• unipolar non-return-to-zero code

Companding is used in the case of signals

• having uniform amplitude distribution

• having large peak-to-peak amplitude but small average power

• having a large peak at high amplitude levels in their amplitude probability density function

• with large average powers

Companding is used in PCM in order to

• keep the quantization noise low for low-amplitude segments of a signal

• avoid quantization noise

• reduce the effect of impulse, or channel noise

• reduce the complexity of the PCM system

Five telemetry signals, each of bandwidth 240 Hz, are to be transmitted simultaneously by 8 bit binary PCM code. The signals must be sampled at least 20% above the Nyquist rate. Framing and synchroniz­ing requires an additional 1% extra bits. The minimum bandwidth required to transmit the multiplex signal is

• 115.2 Hz

• 205.4 Hz

• 136.5 Hz

• 88.6 Hz