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The characteristic impedance of a coaxial wire line is of order
For a coaxial cable with air dielectric and a shield of a given inner diameter, the attenuation is minimized by choosing the diameter of the inner conductor to give a characteristic impedance of 76.7 Ω. When more common dielectrics are considered, the bestloss impedance drops down to a value between 52–64 Ω.
In which manner does current or voltage vary in an analog signal with time?
An analog signal is any continuous signal for which the timevarying feature (variable) of the signal is a representation of some other timevarying quantity, i.e., analogous to another timevarying signal. For example, in an analog audio signal, the instantaneous voltage of the signal varies continuously with the pressure of the sound waves. It differs from a digital signal, in which the continuous quantity is a representation of a sequence of discrete values which can only take on one of a finite number of values.
If an antenna radiates electromagnetic waves from a height h, then the range d upto which the signal can be detected is given by (R is the radius of the earth)
Let O be the centre and R is the radius of the earth. PQ is a T.V. antenna of height h. Two tangents QT and QS are drawn from the top Q of the tower. T.V. signal can reach to the point S and T only not at other area:
∠QTO=90[TO⊥QT]
In ΔQTO,
OQ2=OT2+TQ2
OQ=R+h, QT=d, OT=R,
(R+h)2=R2+d2
R2+h2+2Rh=R2+d2
d2=h2+2Rh h⋘R neglect
d2=2Rh
d= √2Rh
Super high frequencies of __________ are used in Radar and Satellite Communication.
Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one to ten centimetres.
The bandwidth sufficient for commercial telephonic communication:
For speech signals (as in telephone) frequency range 300 Hz 3100 Hz is adequate i.e., a speech signal requires a bandwidth of 2800 Hz.
Optical communication using fibres is performed in the frequency range of
Optical communication using fibers is performed in the frequency range of 1 THz to 1000 THz (microwaves to ultraviolet). An optical fiber can offer a transmission bandwidth in excess of 100 GHz.
Modes of communication system are classified into :
If the area of a TV telecast is to be doubled, then height of transmitting antenna will have to be
Distance of receiving antenna a from transmitting antenna is d = √(2Rh) i.e. d ∝ √h area covered ∝ d2 that is area covered ∝ h. Hence if the area is double, the height of the antenna will also be doubled.
With the increase in frequencies more than 2 MHz, Ground wave propagation
The ground wave is the preferred propagation type for long distance communication using frequencies below 3 MHz (the earth behaves as a conductor for all frequencies below 5 MHz). The ground wave is also used for short distance communications using frequencies between 3 and 30 MHz.
What should be the approximate height of antenna if the TV telecast is to cover a radius of 100 km?
Here , d=100km=100×10^{3}m,
R=6.4×10^{6}m
d=√2Rh
or h=d^{2}/2R=(100×10^{3})^{2}/2×6.4×10^{6}=781.25m
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