19-04-2018, 03:06 PM
(This post was last modified: 19-04-2018, 03:20 PM by peter scott.)
I think I understand most of the details in this test pattern but I don't understand the descriptions relating to the verticals labeled 325 - 575 and 50 to 300.
The Wikipedia explanation is "The thin lines marked from 575 to 325 on one side and 300 to 50 on the other side referred to lines of resolution."
Which doesn't make much sense to me. A more likely explanation is that they display the level of overcompensation in the high frequency response and is described in more detail here:
http://www.rfcafe.com/references/radio-n...n-news.htm
"When the receiver system is overcompensated at, the high frequencies, so that a definite peak results, then a process known as "ringing" will take place. We check for "ringing" with the two columns of single rectangular areas located on either side of the inner circle. The numbers (50, 300, 325, and 575) indicate the width of the nearest rectangle, the width being given as the number of lines which could be accommodated vertically in the image. If over-compensation or "ringing" is present, the rectangles will be followed on the screen by multiple rectangles somewhat similar to ghost images, but evenly spaced from each other. This can be explained as follows.
When a signal containing high-frequency components is applied to this system, the effect, if sudden enough, will produce a series of high-frequency oscillations. These oscillations generally die out rapidly, but before they do, they place several small lines on the screen, each evenly spaced from the original sharp line (or rectangle) that produced them. The lines are produced by the negative peaks of each oscillatory cycle. Not all the oscillations produce visible marks on the screen. Generally only the first two or three are able to do this, depending on the extent of the over-compensation."
I can understand that the overshoot might vary when presented with the different widths in the 50 to 300 column but what I don't understand is the fact that the widths in the the 325 - 575 column are all the same and are in fact wider than that adjacent to the 300 label.
Can anyone explain?
Thanks,
Peter
The Wikipedia explanation is "The thin lines marked from 575 to 325 on one side and 300 to 50 on the other side referred to lines of resolution."
Which doesn't make much sense to me. A more likely explanation is that they display the level of overcompensation in the high frequency response and is described in more detail here:
http://www.rfcafe.com/references/radio-n...n-news.htm
"When the receiver system is overcompensated at, the high frequencies, so that a definite peak results, then a process known as "ringing" will take place. We check for "ringing" with the two columns of single rectangular areas located on either side of the inner circle. The numbers (50, 300, 325, and 575) indicate the width of the nearest rectangle, the width being given as the number of lines which could be accommodated vertically in the image. If over-compensation or "ringing" is present, the rectangles will be followed on the screen by multiple rectangles somewhat similar to ghost images, but evenly spaced from each other. This can be explained as follows.
When a signal containing high-frequency components is applied to this system, the effect, if sudden enough, will produce a series of high-frequency oscillations. These oscillations generally die out rapidly, but before they do, they place several small lines on the screen, each evenly spaced from the original sharp line (or rectangle) that produced them. The lines are produced by the negative peaks of each oscillatory cycle. Not all the oscillations produce visible marks on the screen. Generally only the first two or three are able to do this, depending on the extent of the over-compensation."
I can understand that the overshoot might vary when presented with the different widths in the 50 to 300 column but what I don't understand is the fact that the widths in the the 325 - 575 column are all the same and are in fact wider than that adjacent to the 300 label.
Can anyone explain?
Thanks,
Peter