০১। 24 telephone channels are frequency division multiplexed using an SSB modulation. Assuming 3 kHz per channel, the required band width is
ক) 8 kHz
খ) 27 kHz
গ) 21 kHz
ঘ) 72 kHz
০২। 24 telephone channels, each band limited to 3.4 kHz are to be time division multiplexed using PCM. If sampling frequency is 10 kHz and number of quantization levels is 128, the required bandwidth of PCM is
ক) 1.68 MHz
খ) 240 kHz
গ) 81.6 kHz
ঘ) 3.072 MHz
০৩। 24 telephone channels, each band limited to 3.4 kHz, are to be time division multiplexed by using PCM, calculate the bandwidth of PCM system for 128 quantization levels and an 8 KHz sampling frequency
ক) 192 kHz
খ) 2 MHz
গ) 1.299 MHz
ঘ) 1.54 MHz
০৪। A (75 - j 50) Ω load is connected to a coaxial line of Z0 = 75 Ω at 10 GHz. The best method of matching consists of using
ক) a capacitance at some specific distance from load
খ) a short circuited stub at some specific distance from load
গ) an inductance at load
ঘ) a short circuited stub at load
০৫। A + 1.9 lens has a focal length of 25 mm. The diameter of lens is about
ক) 13 mm
খ) 1.3 mm
গ) 130 mm
ঘ) none of the above
০৬। A 1 MHz sinusoidal carrier is amplitude modulated by a symmetrical square wave of period 100 μ sec. Which of the following frequencies will not be in the modulated signal?
ক) 990 kHz
খ) 1010 kHz
গ) 1020 kHz
ঘ) 1030 kHz
০৭। A 100 + j 100 Ω load is to be matched to a line with Z0 = 300 Ω to give SWR = 1. The reactance of stub is
ক) j 200 Ω
খ) -j 200 Ω
গ) j 100 Ω
ঘ) -j 100 Ω
০৮। A 1000 kHz carrier is simultaneously modulated by 300 Hz and 2 kHz audio sine wave. Which of the following frequencies will not be present in the output?
ক) 998 kHz
খ) 999.7 kHz
গ) 1000.3 kHz
ঘ) 700 kHz
০৯। A 1000 kHz carrier is simultaneously modulated with 300 Hz, 800 Hz and 2 kHz audio sine waves. The frequencies present in the output will be
১০। A 1000 kHz carrier is simultaneously modulated with 300 Hz, 800 Hz and 2 kHz audio sine waves. Which of the following frequency is least likely to be present in the output?
ক) 1002 kHz
খ) 1000 kHz
গ) 999.2 kHz
ঘ) 998.0 kHz
১১। A 1000 kHz carrier wave modulated 40% at 40000 Hz is applied to a resonant circuit tuned to a carrier frequency and having Q = 140. What is the degree of modulator after transmission through the circuit?
ক) 40%
খ) 20%
গ) 0.27
ঘ) 0.54
১২। A 200 Hz sound wave is to be transmitted by a 1000 kHz radio wave using frequency modulation. The instantaneous frequency variation will be
ক) 100 times a second
খ) 200 times a second
গ) 400 times a second
ঘ) 1000 times a second
১৩। A 300 Hz sound wave of intensity 20 dB is transmitted by a 1500 kHz radio wave by frequency modulation. It is seen that instantaneous frequency varies between 1500.2 kHz and 1499.8 kHz, 300 times a second. If the intensity of sound wave is 100 dB.
ক) The instantaneous frequency variations will be between 1500.2 and 1499.8 kHz, 1500 times a second
খ) The instantaneous frequency variations will be between 1501 and 1499 kHz, 1500 times a second
গ) The instantaneous frequency variations will be between 1501 and 1499 kHz, 300 times a second
ঘ) The instantaneous frequency variations will be between 1501 and 1499 kHz, 60 times a second
১৪। A 360 W carrier is simultaneously modulated by two audio wave with modulation percentage of 55 and 65 respectively. Total sideband power radiated will be
ক) 500 W
খ) 360 W
গ) 180 W
ঘ) 130 W
১৫। A 400 W carrier is amplitude modulated with m = 0.75. If single side band suppressed carrier is used the total power in modulated wave is
ক) 400 W
খ) 512 W
গ) 112 W
ঘ) 56 W
১৬। A 400 W carrier is amplitude modulated with m = 0.75. The total power in AM is
ক) 400 W
খ) 512 W
গ) 588 W
ঘ) 650 W
১৭। A 400 W carrier is modulated to a depth of 75 percent. The total power in modulated wave will be
ক) 38.5 W
খ) 400 W
গ) 512.5 W
ঘ) 615.5 W
১৮। A 5000 W signal is attenuated by - 196 dB. The resultant signal strength is
ক) 1.26 x 106 W
খ) 1.26 x 10-2 W
গ) 1.26 x 10-8 W
ঘ) 1.26 x 10-16 W
১৯। A balanced modulator circuit uses
ক) two identical diodes with same V-I characteristics