18-06-2017, 09:21 PM
The "correct" bandwidth for a given number of lines and aspect ratio is a bit of a moveable feast. Nominally there's equal H and V resolution, nowadays expressed in pixels across against lines down. Simple calculation but....
Especially in interlaced systems the apparent vertical resolution is less than it might appear from the number of lines. This is the so-called Kell Factor, named after Raymond Kell: https://en.wikipedia.org/wiki/Kell_factor This article isn't well written and seems to contain serious errors (I don't think Mertz and Gray claimed a Kell Factor of 0.53 for example) but at least it introduces the subject.
If you allow for the Kell effect you can get away with less bandwidth than needed for equal H and V resolution. Hence modern TV systems do this. But 405 "System A" did not. It has always been seen as having rather more BW than strictly necessary.
Especially in interlaced systems the apparent vertical resolution is less than it might appear from the number of lines. This is the so-called Kell Factor, named after Raymond Kell: https://en.wikipedia.org/wiki/Kell_factor This article isn't well written and seems to contain serious errors (I don't think Mertz and Gray claimed a Kell Factor of 0.53 for example) but at least it introduces the subject.
If you allow for the Kell effect you can get away with less bandwidth than needed for equal H and V resolution. Hence modern TV systems do this. But 405 "System A" did not. It has always been seen as having rather more BW than strictly necessary.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
