Communication Systems - Part 1

Communication Systems Preparation Part 1

A cordless telephone using separate frequencies for transmission in base and portable units is known as

Duplex Arrangement. Separate frequencies for transmission from base and portable units allows two way transmission and is called duplex arrangement


For attenuation of high frequencies we should use

Shunt capacitance. Since Xc for high frequencies is low, the high frequencies are shunted to ground and are not transmitted.


A modem is classified as low speed if data rate handled is

Upto 600 bps. When data rate in bits per second is upto 600, modem is low speed.


VSB modulation is preferred in TV because

It reduces the bandwidth requirement to half. VSB (vestigial side band) transmission transmits one side band fully and the other side band partially thus, reducing the bandwidth requirement


A woofer should be fed from the input through a

Low pass filter. Woofer is a low frequency loud speaker covering the range 16 Hz to 500 Hz.


The colour subcarrier and sidebands produced by its modulation with the chrominance signals are accommodated in the standard channel width by the process of

Frequency interleaving . In frequency interleaving the space between bundles is used for colour signaL.


In FM signal with a modulation index mf is passed through a frequency tripler. The wave in the output of the tripler will have a modulation index of

3mf. Frequency multiplier increase the deviation. The modulation index mf is ratio of deviation of frequency to


In colour TV receiver, varactor diode is used for

Tuning. In varactor diode the applied reverse bias controls the width and therefore capacitance of depletion layer. This capacitance is used for tuning.


The number of noise sources in a BJT are

3. Shot noise, partition noise and thermal noise.


Energy content of atmospheric noise

Decreases as frequency is increased. Atmospheric noise decreases as frequency is increased.


A 400 W carrier is amplitude modulated with m = 0.75. The total power in AM is

512 W. Power to be multiplied by one plus square of m divided by 2 i.e m^2/2


c(t) and m(t) are used to generate an FM signal. If the peak frequency deviation of the generated FM signal is three times the transmission bandwidth of the AM signal, then the coefficient of the term cos [2p(1008 x 103t)] in the FM signal (in terms of the Bessel Coefficients) is

5 J4(6). As, we known FM, s(t) Frequency deviation = 3 . (AM Bandwidth) = 6 fm and β= 6 is given in (d) only. ωc + n ωm = (1008 x 103)2pi 2p x 106 + n. 4p x 103 = (1008 x 103).2pi n = 4 So, β = 6, n = 4 hence answer is 5j4(6).


Non-coherently detection is not possible for

PSK. Because in PSK modulation technique the phase of the modulated is changed according to the phase of the baseband signal.


Tracking of extra terrestrial objects requires

high transmitting power, very sensitive receiver, fully steerable antenna. Because in PSK modulation technique the phase of the modulated is changed according to the phase of the baseband signal.


Tracking of extra terrestrial objects requires

high transmitting power, very sensitive receiver, fully steerable antenna.


Free space does not interfere with normal radiation and propagation of radio waves

Free space has no magnetic or gravitational fields.


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