Advertisements
Advertisements
प्रश्न
State three important factors showing the need for translating a low frequency signal into a high frequency wave before transmission
Advertisements
उत्तर
Sound waves of frequency 20–20,000 Hz cannot be transmitted from a radio transmitter by converting them into electrical waves directly. Such low frequency signals need to be translated into high frequency waves before transmission. Three reasons for this are
i. For efficient transmission and reception, the transmitting and receiving antennas must have lengths equal to quarter wavelength of the audio signal. Setting up vertical antennas of such size is practically impossible.
ii. The energy radiated from an antenna is practically zero. The power radiated at audio frequency is quite small; hence, transmission occurs in loss.
iii. The various information signals transmitted at low frequency get mixed and hence cannot be distinguished
APPEARS IN
संबंधित प्रश्न
The carrier wave is given by
C(t) = 2sin(8πt) volt.
The modulating signal is a square wave as shown. Find modulation index.
A carrier wave of peak voltage 15 V is used to transmit a message signal. Find the peak voltage of the modulating signal in order to have a modulation index of 60%
In a communication system, what is meant by modulation?
The carrier wave is represented by
In the block diagram of a simple modulator for obtaining an AM signal, shown in the figure, identify the boxes A and B. Write their function.
Given modulation index physical significance .For an amplitude modulated wave, the maximum amplitude is found to be 10 V while the minimum amplitude is 2 V. Determine the modulation index μ ?
Answer the following question.
Why a signal transmitted from a TV tower cannot be received beyond a certain distance? Write the expression for the optimum separation between the receiving and the transmitting antenna.
I-V characteristics of four devices are shown in Figures.
 |
 |
 |
|
| (i) | (ii) | (iii) | (iv) |
Identify devices that can be used for modulation.
A 25 m long antenna is mounted on an antenna tower. The height of the antenna tower is 75 m. The wavelength (in meter) of the signal transmitted by this antenna would be ______.
A carrier wave Vc(t) = 160 sin(2π × 106t) volts is made to vary between Vmax = 200 V and Vmin = 120 V by a message signal Vm(t) = Am sin(2π × 103t) volts. The peak voltage Am of the modulating signal is ______.
