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What type of antenna used in the mobile?

Answer is Omni directional antenna used in the mobile. There are various types of antenna used in mobile like, PIFA (Polar Inverted F Antenna) FICA etc

Radar Equation

The power Pr returning to the receiving antenna is given by the radar equation:

P_r = {{P_t G_t  A_r \sigma  F^4}\over{{(4\pi)}^2 R_t^2R_r^2}}

where

  • Pt = transmitter power
  • Gt = gain of the transmitting antenna
  • Ar = effective aperture (area) of the receiving antenna
  • σ = radar cross section, or scattering coefficient, of the target
  • F = pattern propagation factor
  • Rt = distance from the transmitter to the target
  • Rr = distance from the target to the receiver.

In the common case where the transmitter and the receiver are at the same location, Rt = Rr and the term Rt² Rr² can be replaced by R4, where R is the range. This yields:

P_r = {{P_t G_t  A_r \sigma  F^4}\over{{(4\pi)}^2 R^4}}.

This shows that the received power declines as the fourth power of the range, which means that the reflected power from distant targets is very, very small.

The equation above with F = 1 is a simplification for vacuum without interference. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment. In a real-world situation, pathloss effects should also be considered.

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Sunday, July 19, 2009

SAMPLING THEORM VERIFICATION

AIM: To verify the sampling theorem and to draw the output graphs.
APPARATUS:
1. Transstor BC107 - 1
2. Resistor 4.7k - 1
3.3k - 1
2.2k - 1
1k - 1
3. Capacitor 1.59µf-1
4. Function generator - 2
5. Regulated power supply-1
6. Dual trace C.R.O - 1
7. Bread board - 1
8. C.R.O probes
9. Connecting wires
PROCEDURE:1). Connect the circuit as per the ckt diagram.
2).The amplitude and frequency of the sinusoidal
Signal of 5Vp-p & 100Hz should be kept constant.
3).By keeping the amplitude of the square wave constant of 10Vp-p & by varying the frequency of the square wave note down the values of no. of samples taken per cycle on seeing in C.R.O.
4).By gradually increasing the frequency of square wave tabulated the resultant values.
5). Apply the sampled signal to the integration and reproduce the original sinusoidal signal.
6).Observe the reproduced signal on C.R.O and compare with original signal.
THEORY:A band limited signal which has no spectral components above a frequency fm is uniquely determined by its values taken at uniform intervals less than 1/2fm seconds apart. The sampling square wave Vs which determines the time intervals in which the samples should be taken from the modulating voltage signals Vm. By adjusting the frequency of square wave. The no.of samples taken per cycle of the modulating signal can be altered.
If the no.of samples taken per cycle is less than it will become difficult to detect the actual signal from that samples.
On passing these samples through an integrator circuit will again reproduce the actual signal. The reproduced signal will be fair if the no.of samples taken per cycle is high otherwise it should be unfair. So the no.of samples/cycles will decide the reproduced signal quality.
PRECAUTIONS:
1. Check the connections before switch on the power supply.
2. Avoid loose connections.
3. Observe the output on C.R.O and take the readings without parallax error.
RESULT:
VIVA VOICE:

1.Define the sampling theorem in time domain and freq domain?
2. What do you mean by Nyquist rate interval?
3.What is meant by aliasing?
4. What is the difference between ISI&aliasing?
5. What is the Aim of sampling theorem?
6. What is the use of sampling theorem?
7. What is the condition to take for sampling a signal for faithful reproduction of signal?

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