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LECTURE 5-6. receivers OF RADIO and TV broadcastING systems. GENERAL INFORMATION ABOUT RECEIVERS OF RADIO AND TV BROADCASTING SYSTEMS MAIN TYPES OF BROADCASTING RECEIVERS RECEIVER NOISE FACTOR AND SENSITIVITY (SENSEPTIBLITY) MAIN ELEMENTS OF RECEIVERS SOFTWARE DEFINED RADIO (SDR).
1. GENERAL INFORMATION ABOUT RECEIVERS OF RADIO AND TV BROADCASTING SYSTEMS
The general block diagram of radio channel of thebroadcast and TV systems
A sound or image, is transformed in voltage or current, modulates a high-frequency carrier. As a result the output radio signal (RS) of TX can be amplitude, phase or frequency modulated
The radioreceivers is designed to extraction of useful signals received from the receiving antenna, its amplification and conversion to the form required for the normal operation of terminals (loudspeaker, monitor, etc.)
By apointment: radio broadcasting, TV broadcasting, wireless communication, navigation, radiolocation, radio control, etc.
By type of signal:analog or digital
By the method of signal processing:
- with filter processing;- with correlation-filter processing.
By frequency band:LF, MF, SF, VHF, UHF, SHF, et cetera
The main functions of radio receivers: the selectivity (separation of the useful signal); amplification (to the level required for normal working terminal); conversion (to increase selectivity and stable amplification); automatic gain control (for widening dynamic rang) ; demodulation (selection of modulation law) or measure the signal parameters.
Sensitivity - the minimum power or voltage at the input RX, which provide a given quality of signal processing
Peak (noise-limited) sensitivity - the minimum power Psmin or voltage Uc minat the receiver input at which the SNR at the output of the linear part RX equal to one (Ps / Pn = 1 or Uc / Un = 1); Real (actual or threshold) sensitivity - minimum power or voltage at the receiver input at which the predetermined reception quality (given the SNR at the output of the linear part RX). At wavelength > 1 m, when the resonans circuits RX can be considered as systems with lumped parameters, the sensitivity is taken in units of voltage - microvolts or millivoltsUc min. If <1 m - in terms of power Pc min. Real sensitivity radio receiver is in the range of 50 ... 300 μV, depending on the quality class. Sensitivity of satellite TV receiver can be up 10-14 ... 10-15 W.
For broadcast receivers with ferrite antenna uses the concept of sensitivity in field strength. It has a value from 0.3 to 5 mV/m.
Block diagram of the receiver of direct amplification
. The block diagram of a superheterodyne receiver
2. MAIN TYPES OF BROADCASTING RECEIVERS
Block diagram of direct conversion receivers
Frequency range - the entire band of frequencies, which can receive signals
Dynamic range RX describes its ability to receive signals without distortion
Selectivity: by the frequency (on the next channel, the image channel) by the waveform, by the polarization
Thermal (heat) noise
Power rating (nominal power)
– noise power at matched load
Noise power output
Power output noise, converted to the input
Balanced frequency converter
Demodulation of PM signal
Ud1= U0 + Us /2; Ud2= U0 - Us /2.
m << 1
Us/U0 = m
m = 1
Output voltage phase detector for in-phase input and reference signals φ =0
is proportional to the input signal Us, and the phase detector is converted in the synchronous detector. These detectors, due to their high linearity, are widely used in analog TV for demodulation of the image signals and in digital TV for demodulating PSK signals.
Matched filter –Main IFA
f IF= |f1 – fs |
Block diagram of the analog – digital receiver
For ADC 1107ПВ2
L FT , MHz D, dB
For ADC AD9260 L=16
The twentieth century saw the explosion of hardware defined radio (HDR) as a means of communicating all forms of audible; visual, and machine-generated information over vast distances.
Most radios are hardware defined with little or no software control; they are fixed in function for mostly consumer items for broadcast reception. They have a short life and are designed to be discarded and replaced.
Software defined radio (SDR) uses programmable digital devices to perform the signal processing necessary to transmit and receive baseband information at radio frequency. Devices such as digital signal processors (DSPs) and field programmable gate arrays (FPGAs) use software to provide them with the required signal processing functionality. This technology offers greater flexibility and potentially longer product life, since the radio can be upgraded very cost effectively with software.
SDRequipment - these are elements of the wireless network which operating modes and parameters can be changed or expanded after the elements are made using the software.
can to present by sum of two quadrature component
One cycle Sine Wave at Sampled Frequency Fo