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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

DIFFERENTIAL PULSE CODE MODULATION

AIM: To study the operation of differential pulse code modulator and Demodulator.
APPARATUS:
1. DPCM modulator trainer kit.
2. DPCM demodulator kit.
3. Storage oscilloscope.
4. Digital multimeter.
5. Coaxial cables.
6. C.R.O. probes & connecting wires.
THEORY:
In this DPCM redundancy is reduced from over all bit value will decrease and number of bits required to transmit one sample will also be reduced. This type of digital pulse modulation scheme is called differential pulse code modulation.
The differential pulse code modulation works on the principle of predetection . The value of the present sample value is predicted from the samples. The predetection may not be exact but it is very close to the actual sample value , shows the transmitting of differential pulse code modulation system works on the principle of predetection. The present sample value is predicted but it is very close to the actual sample value.
PROCEDURE:1. Verify the circuit as per the circuit diagram.
2. Observe the output of the A.F. generator .it should be a Sine wave of 400 HZ frequency with 5Vp-p
3. Verify the output of the D.C. source.
4. Observe the output of the clock generator using C.R.O. it Should be 64 KHZ and 8 KHZ. Frequency of square Wave with 5Vp-p.
FOR MODULATION:
5. Keep the C.R.O. in dual mode .connect one channel to
8 KHZ signal and another channel to open outputs.
6. Observe the DPCM output with respect to the 8KHZ Signal.
FOR DEMODULATION:
7. Connect the DPCM signal to the demodulator input.
8. Connect the clock signal from transmitter to the receiver Using co-axial cable.
9. Observe the D/A converter output using storage Oscilloscope and compare with the original signal and Observe that there is no information loss in process of Conversion and transmission.
10 . similarly verify for different values of modulating Signal voltage .
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.What is the aim of the experiment ?
2. Wat is DPCM ?
3.What is PCM ?
4. What is the difference between DPCM & PCM ?
5.Why we need coding ?

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