০০। A communication channel with additive white Gaussian noise, has a bandwidth of 4 kHz and an SNR of 15. Its channel capacity is
ক) 1.6 kbps
খ) 16 kbps
গ) 32 kbps
ঘ) 256 kbps
০১। A duplexer is a device used to
ক) feed more than one receiver from a single antenna
খ) connect two transmitters to the same antenna
গ) connect a receiver and a transmitter to the same antenna
ঘ) none of these
০২। A FM signal with modulation index Mf is passed through a frequency doubler. The wave in the output of the doubler will have modulation index of
ক) Mf
খ) Mf/2
গ) 2Mf
ঘ) UMf
০৩। A heterodyne frequency changer is called a
ক) Modulator
খ) Mixer
গ) Demodulator
ঘ) Frequency translator
০৪। A low ratio of the A.C. load impedance of a diode detector results in
ক) diagonal clipping
খ) poor AGC operation
গ) poor AF response
ঘ) negative peak clipping
০৫। A notch filter is sometimes used in communication receivers to
ক) reduce receiver gain at some specific frequency
খ) increase receiver gain at some specific frequency
গ) made selectivity more precise
ঘ) spread the bandwidth
০৬। A padder is basically a/an
ক) insulator
খ) variable resistor
গ) capacitor
ঘ) inductor
০৭। A receiver having an RF amplifier and an IF of 450 kHz, has Q of the coils 65 and an incoming frequency of 1200 kHz. The image rejection of the receiver is
ক) 5870
খ) 3655
গ) 236
ঘ) 13.3
০৮। A receiver having poor IF selectivity will also have poor
ক) sensitivity
খ) double spotting
গ) blocking
ঘ) all of the above
০৯। A transmitter serial current contains
ক) carrier frequencies
খ) audio frequencies
গ) radio frequencies
ঘ) none of the above
১০। A trimmer is basically a
ক) insulator
খ) inductor
গ) capacitor
ঘ) variable resistor
১১। An arbitrary signal m (t) has zero average value and it is bandlimited to 3.2 kHz. It is sampled at the rate of 8 K samples/S. The samples are passed through an ideal bandpass filter with centre frequency of 32 kHz and bandwidth of 6.4 kHz. The output of band pass filter is
ক) AM-DSB signal with suppressed carrier
খ) AM-DSB signal with carrier
গ) AM-SSB signal with carrier
ঘ) a sequence of exponentially decaying sine waves
১২। An unmodulated voltage 10 V effective is applied to a dioxide detector in which load resistance is 4 x 10-5 ohms. A micrometer shows that the rectified DC current in this resistance is 30 A. The efficiency of detection is
ক) 34%
খ) 55.5%
গ) 68.8%
ঘ) 84.7%
১৩। An unmodulated voltage 10 V effective is applied to a dioxide detector in which load resistance is 4 x 10-5 ohms. A micrometer shows that the rectified DC current in this resistance is 30 A. The input resistance of the detector is
ক) 114 kW
খ) 336 kW
গ) 384 kW
ঘ) 455 kW
১৪। As compared to tuned radio frequency receivers which of the following is the advantage of using superheterodyne receivers?
ক) High gain and better sensitivity
খ) Better selectivity at high frequencies
গ) Stability
ঘ) Noise suppression
১৫। Double spotting in a receiver is due to
ক) poor sensitivity of RF amplifier
খ) high gain of IF amplifier
গ) inadequate image frequency rejection
ঘ) all of the above
১৬। EM 84 tube is used in radio receivers as
ক) audio amplifier
খ) RF amplifier
গ) full wave rectifier
ঘ) magic eye
১৭। Fidelity of a receiver represents
ক) the sensitivity expressed in terms of voltage that must be applied to the receiver input to give a standard output
খ) the extent to which the receiver is capable of distinguishing between the desired signal and other frequencies
গ) the variation of the output with the modulation frequency when the output impedance is a resistance
ঘ) none of the above
১৮। FM amplifier in a superheterodyne receiver
ক) increases selectivity
খ) suppresses noise
গ) provides improved tracking
ঘ) improves the rejection of the image frequency
১৯। FM receivers using the standard 88 to 108 MHz band use IF of