 Today we want to see composite video signal for monochrome TV. The learning outcome of this topic is at the end of this session student will be able to explain the concept of composite video signal for monochrome TV. The contents of these topics are composite video signal, camera signal, horizontal line period, horizontal blanking period, horizontal sync pulse and vertical sync plus. First composite video signal. Composite video signal is formed by the electrical signal corresponding to the picture information which to be line scanned in TV camera pickup tube and introduce the sync signal into it. This forms the composite video signal. Composites of the composite video signal. There are basically three components of the composite video signal. First camera signal, second synchronizing pulse, third blanking pulse. And the function of the components, first camera signal corresponding to the variation of light in scene. Synchronizing pulses. To synchronize the scanning add the transmitter as well as receiver. Synchronizing pulse to make the retrace invincible. Composite video signal is formed by the basic three signals that is camera signal, synchronizing pulse and blanking pulse. These three signal combined to make composite video signal. The scanning of the three horizontal lines in image has shown in the next figure. In that figure lower 75% is the camera signal and upper 25% is the synchronizing pulse that is the standard we want to maintain. Now this figure shows the composite video signal. This figure is drawn whole-tage versus time. If you observe this diagram 75% the divide this diagram is divided into two parts. One is from 12.5 to 75 percentage and from 75% to 100%. This up to 75% shows the camera signal and above the 75% to 100% it shows the synchronizing pulse. Now if you observe in this camera signal there are two parts one is a white level part and another one is a dark level part. Out of these two parts the camera signal lower part consist of a white level, upper part consist of a dark signal and above the 75% to 100% the signal called as horizontal synchronization pulse. This horizontal synchronization pulse is used for synchronization at transmitter as well as receiver side. Now one line duration the total time required for this one line duration from this to this is 64 microseconds and this is a contains the picture detail information and the active line period is the time required for that one is 52 microseconds. Camera signal. The camera signal as we discussed there lowest amplitude contains whitish part of the picture and higher amplitude contains the darker part of the picture and the camera signal is transmitted with the help of negative polarity transmission. Now for the transmission of this camera signal there are two types one is negative polarity transmission and another one is positive polarity transmission. Now basically 99% we use the negative polarity transmission because negative polarity transmission it is advantageous over the positive polarity transmission that's why basically all where we use negative polarity transmission. Now this figure shows horizontal blanking period and sink pulse details for one horizontal line. Now if you observe here this is for 75% to 100% is the shown horizontal sink pulse added here 25% is added here. This is a diagram shows vertical sink pulse added here 25% and this is a blanking level. This 160 microsecond is required for vertical blanking pulse period and this contains the picture information and as we discussed this is a part is called as a camera signal and the lower part is called as a peak white level that is present at 12.5% of the overall signal. Now this is called as a black level and this total time required is a 64 microsecond for this horizontal blanking pulse. Now total line period for one horizontal line equal to 64 microsecond. Blanking period required is 12 microsecond. During this blanking synchronization pulse are inserted. This synchronization is used for transmitter as well as receiver side for getting the correct signal at the correct time. The blanking period again consists of three sections first one is a front porch, second one is a line synchronization pulse and third one is a back porch. Now what is the time requirement of this one we can understand with the help of the figure. Now horizontal line period H it is the total duration of one complete horizontal line period is called as horizontal line period. It is given by H is equal to 1 divided by frequency in horizontal direction is equal to 1 upon 15,625 is equal to 64 microsecond therefore horizontal line period is required 64 microsecond. Now this is a horizontal sync and blanking signal standards. Here is the total how much time we require that will be explained here. Now if we observe this diagram the picture display is a total horizontal sync pulse required is a 64 microsecond out of this one 64 microsecond. The picture information is a 52 microsecond and remaining 12 is used for horizontal blanking pulse. As we discussed in the previous slide horizontal blanking pulse is again of three types one is a front porch, second one is a back porch and third one main important that one horizontal synchronization pulse. Now this 12 microsecond is divided into three parts that front porch require 1.5 microsecond this horizontal synchronization pulse require 4.7 microsecond and back porch require the 5.8 microsecond. Now if we observe this diagram here left hand side shows back porch block and here front porch. Now if we observe this back porch time is required for the retrace and when it start from the left hand side if we observe then that time it will be the start the tracing time. And again when it is true to the up to the last end point then it will again goes to the retrace and again it will be the start tracing and this one is the retrace ends here and rest it starts here. This diagram shows horizontal reflection sawtooth versus time. Horizontal blanking period it is the part of each line during which line synchronization pulse is inserted during this period there are two conditions first flyback is initiated and completed and second beam cut off by the black level amplitude of video signal. Horizontal blanking period is equal to 0.19 into H. Now here pause the video and think about the what is the value of H and put the value into it and what is the equation that we get. Now horizontal blanking period is equal to 0.19 into H value is 64 microsecond equal to 12 microsecond means horizontal blanking period requirement is 12 microsecond. Horizontal sync pulse short pulse sent from the transmitter to receiver for synchronization synchronization pulse is used for the synchronization in the transmitter as well as the receiver. Now width requirement is formula is 0.07 into H. H value we know the H value that is the 64 microsecond we put that into here that we get 4.7 microsecond. Now front porch synchronization pulse does not coincide with the blanking pulse but it follows after about the 2% of the line period the short period is called as a front porch. Front porch is equal to 2.5% of width H that is 1.5 microsecond. Now back porch at the blanking level allows plenty of time for retrace to be completed back porch period is 5.8 microsecond it permits time for the horizontal time base circuit to reverse the direction of current for the initialization of scanning for the next time. It provides amplitude and enables the preserve the DC content of the picture information the transmitter and its amplitude is equal to the blanking level. At the receiver blanking level is independent of the picture details. This picture details is utilized in Atomatic gain control circuit. This Atomatic gain control circuit develop the Atomatic gain control voltage that is proportional to the signal strength which picked up at the antenna. Now whichever we calculate the horizontal scanning details of horizontal scanning we again once again we show the help of this table that is periods and time in microsecond. Total line period is 64 microsecond horizontal blanking is 12 microsecond horizontal sync pulse is 4.7 microsecond front porch time is required is 1.5 microsecond and for the back porch it requires 5.8 microsecond. Now we goes to the vertical synchronization pulse. In the 624 line system the vertical sync pulse has a duration of 2.5 line period that is 2.5 into 64 microsecond is equal to 160 microsecond is required for vertical sync pulse. At the end of the first field vertical sync pulse is added during this period that is 312.5 to 350. At the end of the second field another sync pulse is added during the line period of 1 to 2.5. One vertical sync pulse ends at the half line period and other at the full line period. Now the next part is vertical blanking period. It is the period during which picture information is completely suppressed and flyback retrace of field time base is initiated and completed. The duration for vertical blanking period is 20 into line periods. There is a formula is vertical blanking period is equal to 20 h and we know the value of h put that into this equation that is 20 into 64 microsecond that is 1280 microsecond. Now references for this topic is monochrome and color television by R. R Gulati. Thank you.