17-06-2019, 09:49 AM
In Europe these signals are known just as Insertion Test Signal (ITS) because VITS is a swear word in one European language - French, I believe
Trevor, your suggestion that the pulse was at 2.5MHz, if correct, would suggest the British Relay weren't quite as critical in their test methods as the broadcasters.
The pulse is correctly known as a 2T raised cosine pulse. T for a 625 line system is 100nS, so a 2T pulse is 200nS wide at its half way point - it is effective one cycle of a 5MHz sine wave raised so the it is all above black level and sits exactly between black level and peak white. The pulse during the bar is, of course inverted, and extends from peak white to black level.
For 405, T = 166nS so 2T = 333nS - effectively one cycle of a 3MHz signal.
There are no sharp transitions in ITS signals - all of the luminance component passes through the same filter that creates the 2T pulse ensuring that there are no signals above 5MHz (625) or 3MHz (405).
Trevor, your suggestion that the pulse was at 2.5MHz, if correct, would suggest the British Relay weren't quite as critical in their test methods as the broadcasters.
The pulse is correctly known as a 2T raised cosine pulse. T for a 625 line system is 100nS, so a 2T pulse is 200nS wide at its half way point - it is effective one cycle of a 5MHz sine wave raised so the it is all above black level and sits exactly between black level and peak white. The pulse during the bar is, of course inverted, and extends from peak white to black level.
For 405, T = 166nS so 2T = 333nS - effectively one cycle of a 3MHz signal.
There are no sharp transitions in ITS signals - all of the luminance component passes through the same filter that creates the 2T pulse ensuring that there are no signals above 5MHz (625) or 3MHz (405).
