07-02-2013, 09:17 AM
MONOCHROME TELEVISION RECEIVER
[attachment=49924]
INPUT FROM ANTENNA
ANTENNA INTERCEPTS OR PICKS UP ELECTROMAGNETIC WAVES WHICH ARE RADIATED BY TRANSMITTERS.
THE RECEIVED SIGNAL CAN VARY FROM 50 µV TO 1mV.
ANTENNA CAN BE RESONANT OR NON-RESONANT.
YAGI-UDA AND PARABOLIC REFLECTOR ARE MOST COMMON IN USE.
BALUN
THE IMPEDENCE SEEN BY THE ANTENNA AT THE RECEIVER I/P IS ABOUT 300
THE OPEN CIRCUIT IMPEDENCE OF THE ANTENNA IS ABOUT 75.
THE BALUN PROVIDES THE IMPEDNECE MATCH BETWEEN ANTENNA AND THE RECEIVER.
RF AMPLIFIER
RF AMPLIFIER RECEIVES SIGNAL FROM ANTENNA .
IT IS A LOW NOISE AMPLIFIER.
IT PROVIDES INITIAL GAIN AND SELECTIVITY TO THE RECEIVED SIGNAL.
CONVERSION TO I.F.
THE TUNER I/P IS A MODULATED COMPOSITE VIDEO SIGNAL(WITH SOUND).
THE O/P IS AGAIN A COMPOSITE VIDEO SIGNAL BUT WITH A DIFFERENT CARRIER FREQ.,THE INTER MEDIATE FREQ.
THIS CONVERSION INTO I.F. IS DONE BY HETERODYNING I/P SIGNAL WITH LOCAL OSCI. SIGNAL TO PRODUCE BEAT FREQ.
PICTURE I.F.=38.9 MHz & SOUND I.F.=33.4 MHz
AFTER CONVERSION THE SOUND FREQ. IS LOWER THAN PICTURE FREQ.
V.S.B. CORRECTION
IN V.S.B. TRANSMISSION THE UPPER SIDE BAND IS FULLY TRANSMITTED AND LOWER SIDE BAND IS PARTIALLY TRANSMITTED.
THIS PROVIDES BOOSTING OF LOW FREQ. COMPONENTS,UNNECESSARILY.
SO, THEY ARE ATTENUATED BY AN APPROPRIATE FACTOR.
THIS IS CALLED V.S.B. CORRECTION.
REQUIREMENTS
THE DETECOR O/P MUST MAINTAIN DC LEVEL OF THE SIGNAL TO PRESERVE BRIGHTNESS.
THE POLARITY OF O/P OF THE VIDEO DETECTOR SHOULD BE NEGATIVE.
SINCE CATHODE DRIVE IS COMMON PRACTICE ,WHICH REQUIRES POSITIVE POLARITY OF THE VIDEO SIGNAL.
WHILE O/P OF THE VIDEO AMPLIFIER IS INVERTED AS IT IS AN INVERTING AMPLIFIER.
SO, I/P TO VIDEO AMPLIFIER IS NEGATIVE.
[attachment=49924]
INPUT FROM ANTENNA
ANTENNA INTERCEPTS OR PICKS UP ELECTROMAGNETIC WAVES WHICH ARE RADIATED BY TRANSMITTERS.
THE RECEIVED SIGNAL CAN VARY FROM 50 µV TO 1mV.
ANTENNA CAN BE RESONANT OR NON-RESONANT.
YAGI-UDA AND PARABOLIC REFLECTOR ARE MOST COMMON IN USE.
BALUN
THE IMPEDENCE SEEN BY THE ANTENNA AT THE RECEIVER I/P IS ABOUT 300
THE OPEN CIRCUIT IMPEDENCE OF THE ANTENNA IS ABOUT 75.
THE BALUN PROVIDES THE IMPEDNECE MATCH BETWEEN ANTENNA AND THE RECEIVER.
RF AMPLIFIER
RF AMPLIFIER RECEIVES SIGNAL FROM ANTENNA .
IT IS A LOW NOISE AMPLIFIER.
IT PROVIDES INITIAL GAIN AND SELECTIVITY TO THE RECEIVED SIGNAL.
CONVERSION TO I.F.
THE TUNER I/P IS A MODULATED COMPOSITE VIDEO SIGNAL(WITH SOUND).
THE O/P IS AGAIN A COMPOSITE VIDEO SIGNAL BUT WITH A DIFFERENT CARRIER FREQ.,THE INTER MEDIATE FREQ.
THIS CONVERSION INTO I.F. IS DONE BY HETERODYNING I/P SIGNAL WITH LOCAL OSCI. SIGNAL TO PRODUCE BEAT FREQ.
PICTURE I.F.=38.9 MHz & SOUND I.F.=33.4 MHz
AFTER CONVERSION THE SOUND FREQ. IS LOWER THAN PICTURE FREQ.
V.S.B. CORRECTION
IN V.S.B. TRANSMISSION THE UPPER SIDE BAND IS FULLY TRANSMITTED AND LOWER SIDE BAND IS PARTIALLY TRANSMITTED.
THIS PROVIDES BOOSTING OF LOW FREQ. COMPONENTS,UNNECESSARILY.
SO, THEY ARE ATTENUATED BY AN APPROPRIATE FACTOR.
THIS IS CALLED V.S.B. CORRECTION.
REQUIREMENTS
THE DETECOR O/P MUST MAINTAIN DC LEVEL OF THE SIGNAL TO PRESERVE BRIGHTNESS.
THE POLARITY OF O/P OF THE VIDEO DETECTOR SHOULD BE NEGATIVE.
SINCE CATHODE DRIVE IS COMMON PRACTICE ,WHICH REQUIRES POSITIVE POLARITY OF THE VIDEO SIGNAL.
WHILE O/P OF THE VIDEO AMPLIFIER IS INVERTED AS IT IS AN INVERTING AMPLIFIER.
SO, I/P TO VIDEO AMPLIFIER IS NEGATIVE.