A Discone antenna is
It is a combination of disc and cone in close approximity.
In a two tone AM system the two modulating frequencies are 2000 p and 4000 p rad/sec. If carrier frequency is 2p x 106 rad/sec the frequencies of upper sidebands are
For a system to be designated as hi-fi, the signal to noise ratio should be at least
Hi-Fi system has a ratio at least equal to 50 dB.
Dolby system of noise reduction divides the total audio spectrum into
Dolby A system divides the frequency in 4 bands viz.f < 80 Hz, 80 Hz < f < 2999 Hz, f > 3000 Hz, f > 9000 Hz.
In a system an input resistance of 20 kΩ causes a noise voltage of 15μV. If two such input resistances each of 20 kΩ are used in parallel, the total noise voltage will be about
Overall resistance = 10 kW. Noise voltage = (15) = 10.6 μV.
In the television system in India, the odd and even fields are scanned
Each field is scanned 25 times but alternately.
Consider the following
All are correct.
Vidicon and plumbicon operate on the principle of
Photo conduction uses the fact that resistivity of some materials depends on intensity of light falling on their surface.
The typical squelch circuit
To suppress noise when carrier is absent, squelch circuit cuts off audio amplifier.
A TV receiver has a width of 60 cm. The aspect ratio is 4/3. The required EHT supply is about
EHT supply is 1 kV per diagonal inch.
Height = 60 x = 45 cm.
Diagonal = .
A narrow band noise n(t) has symmetrical spectrum and has power density spectrum 0.2 x 10-6. The power density of quadrature component is
The radio receivers mostly used now a days are
Now-a-days only super heterodyne radio receivers are used.
The reactance of coupling capacitors, for DC quantities, is
For zero frequency capacitive reactance is infinite.
An AM wave is given by s(t)AM = 20 (1 + 0.5 cos 103t + 0.3 cos 104 t cos 106 t) the modulation index of the envelope is
The modulating frequency in frequency modulation is increased from 10 kHz to 30 kHz. The bandwidth is increased by
BW = 2fm(1 + β)
for β >> 1
B.W. a 2fm .
A sinusoidal signal with peak to peak amplitude of 1.536 volt is quantized into 128 levels using a mid-rise uniform quantizer. The quantization noise power is
An FM wave is made to pass through a frequency tripler. If original modulation index is mf, the output of tripler has a modulation index equal to
Frequency tripler makes modulation index three times.
A balun provides an impedance transformation of
Balun has turn ratio of 2 : 1. Therefore, impedance transformation is 4 : 1.
A signal m(t) with bandwidth 500 Hz is first multiplied by a signal g(t) where . The resulting signal is then passes through an ideal low pass filter with bandwidth 1 kHz the output of the low pass filter would be
Multiplication in time domain is equivalent to convolution. According to the property of impulse signal, convolution of a signal m(t) with δ(t) is signal itself.
m(t) x g(t)
If γ = (S0/N0)/(Si/Nm) where S0 and S1 are signal power output and signal power input and N0 and Nm are noise power output and noise power input, the value of γ for SSB-SC and DSB-SC amplitude modulated system respectively are
SSB - SC and SSB - DB have γ = 1 and are similar from noise point.
Consider the draw backs
In delta modulation the, recovered waveform may be dc whereas the original signal is not dc. This noise is called granular noise.
It is required to increase the maximum range of a radar by a factor of two. The peak power transmitted in the radar system has to be increased by a factor of
Range μ (Power)0.25
A source generates three symbols with probabilities 0.25, 0.25, 0.50 at a rate of 3000 symbols per second. Assuming independent generation of symbols, the most efficient source encoder would have average bit rate is as
Use Shannon Fano coding.
(0.25) is encoded as 01
Number of bits/sec
= 0.25 x 3000 x 2 + 0.25 x 3000 x 2 + 0.5 x 3000
Armstrong F.M. transmitter performs frequency multiplication in stages
where (Δf) is the frequency deviation.
The filter circuit for feeding tweeter has
Series capacitance and shunt inductance is high pass circuit.