LECTURE 5-6. RECEIVERS OF RADIO AND TV BROADCASTING SYSTEMS

1. GENERAL INFORMATION ABOUT RECEIVERS OF RADIO AND TV BROADCASTING SYSTEMS

2. MAIN TYPES OF BROADCASTING RECEIVERS

3. RECEIVER NOISE FACTOR AND SENSITIVITY (SENSEPTIBLITY)

4. MAIN ELEMENTS OF RECEIVERS

5. SOFTWARE DEFINED RADIO (SDR)

Sound and (or)

image transducer

TX RX Оконечное устройство

Interference

RS RS+ interference

1. GENERAL INFORMATION ABOUT RECEIVERS OF RADIO AND TV BROADCASTING SYSTEMS

The general block diagram of radio channel of the broadcast 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

00cos tttttUtU

Interference. At propagation radio signal in free space and feed lines it take place distortions, which are conditioned:

•by irregularity of propagation medium;

•by the artificial and natural restriction ;

•by internal noises of antenna and receiver and its imperfection

Radio receiver (RX) intended for transformation input signals with the purpose of extraction of useful information. RX must contain units, necessary for realization of the followings operations:•selection from all of aggregate of electric vibrations, pointed in aerial the external electromagnetic fields, signal from a necessary radio transmitter;• amplfication of high-frequency signals;• demodulation signals;•strengthening of prorectifying signal.

The radio receivers 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.

Peak (noise-limited) sensitivity - the minimum power Psmin or voltage Uc min at 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 millivolts Uc 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.

Sensitivity - the minimum power or voltage at the input RX, which provide a given quality of signal processing

2. MAIN TYPES OF BROADCASTING RECEIVERS

Block diagram of the receiver of direct amplification

. The block diagram of a superheterodyne receiver

f p

УНЧСМ

Гетеродин

УВЧf p

f г = f р

U гр

U c

Block diagram of direct conversion receivers

SDR RX

Frequency Converter

Parameters of the radio receivers Frequency range - the entire band of frequencies, which can receive signals minmax fff

Dynamic range RX describes its ability to receive signals without distortion

D,дБ=10 lg(Pinmax/Pin min)

Pвых

Selectivity: by the frequency (on the next channel, the image channel) by the waveform, by the polarization

ПвыхПвх P/PB дБ70...50Plg10Plg10B, ПвыхПвхдБ у

2

c

ПЧ

зерк Qf

f41B

Ls

nn RR

Р

2

U2

RРR n

nL 4

UR

2

0

n

n

П

Р 00N

002 I2 nsnn ПeII

nn kTRПU 42т

0шР

– noise power at matched load

0n nÐ kTÏ

Power rating (nominal power)

RCП

2

10,7

22

70

0,7

221

1

fП

П

RCffy

,

7,0

022

7,0

20,7

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fП

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fП

ПdffyПn

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4 n

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Quantitative estimation of noises

0

22 a

1

2a

xarctg

a

1

xa

dx

Shot noise

Thermal (heat) noise

Nyquist formula

Shottky formula

Stored energy

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IFA

рLNA

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Т

К

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IFA

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MIX

рIN

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n

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n

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inШc PP )/(

INPUT.UNIT Detector

G

LNA MIX IFA

3. RECEIVER NOISE FACTOR (figure, ratio)

outns

innsRX РР

PPn

)/(

)/(

...11

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IFA

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MIXLNARX KК

n

К

nnnIf КрIN ≈1

pININшIN Kdn /1

outШc PP )/(

)1(00 RXnRXnnRXn nПkTПkTПkTP

RXRXRX TTn 0/1 11/ 0 RXRXRX TTn

1pINK

NOISE OF RECEIVER ANTENNA

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Power output noise, converted to the input

k =1,38·10-23 W/Hz grad

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naa

a

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0aa T/T

Rs=Ra RL=Rin

1/ 0 шRXRXRX nTT → 1 RXшn

nn

нLs

nn KT

R

KTRR

RR

UP

4

4

)(2

2

nn kTRПU 42т Nyquist formula

Noise power output

)()(1 00min аRXnаRXnаnRXns ТТkППkTnПkTР

RECEIVERS SENCITIVITYRECEIVERS SENCITIVITY

f)()(

fff exp

WPP

ldW

AnsRXinns

4. MAIN ELEMENTS OF RECEIVERS

Balanced frequency converter

Low-nose amplifier

Demodulators (detectors)

UKU ut АМo

fKU FМout

PМout KU

— AM

— PM

Amplitude detectors

LR

FС

U LFout

Fbl СС

intmU

HF

D

FR

— FM

LF

Demodulation of PM signal

Demodulation of ASK signal

а

б

в

Phase detector

cos21cos21 220 mmmmUКU дout

2sin

2cos2

sдout UКU

cos2 sдout UКU m << 1

m = 1

Us/U0 = m

Output voltage phase detector for in-phase input and reference signals φ =0

sдout UКU 2

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.

Synchronous detector

U d1= U 0 + Us /2; U d2= U0 - Us /2.

Frequency detector

dttutuz )()()( 21

comproutns KPP )1/2()/( 2

outinoutincompr ПfffK //

)1(0min

nRX

compr

inS n

K

fkTP

Var. time delay

x filter

ucd( )

u1(t)

u2(t)

u1(t- )

Correlated detector

expansioncompression

LNA MIX PreIFA

FS

Matched filter –Main IFA

X_

Main IFA PD

PD

АD LFA

ADC

ADC

DAC90o

DSP

рBHFSмin

inDETuIFA

КP

UK

BHF BIF BD BLF (BDP)

f IF= |f1 – fs |

AGC

24

1

Q

f

fB

s

IFmirr

Block diagram of the analog – digital receiver

f1

f2

ninninрADCn

nADCnADC ПkTR

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КP

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2

0

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n

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n

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L FT , MHz D, dB

ADC have not affected on RX noise factor

If only

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.

Software Defined Radio (SDR)SDR equipment - 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.

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can to present by sum of two quadrature component

.sincos

sincossin)](sin)([cos)](cos)([)(

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22 QI

One cycle Sine Wave at Sampled Frequency Fo

Zero IF Quadrature Product Detector