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Date Posted: 16:10:08 02/18/02 Mon
Author: Tom
Subject: Re: Blanking durring VBI
In reply to: Jain 's message, "Re: Blanking durring VBI" on 05:18:42 02/18/02 Mon

Most systems suppress the VBI as well as the HBI. SSAVI is the only system I know that does not suppress or raise the VBI, although I'm sure there are many others. If the VBI is suppressed, there is no valid black level in the VBI.

To detect whether the video is scrambled or not can be done in several ways. To do it without adding hardware, look for the PED that is produced as the HBI becomes raised. If it is not there, then it is a normal signal. To do it with more hardware, sample the sync and compare it with a reference voltage. If the sample is higher than the reference, then the signal is scrambled. The reference voltage would need to be adjusted by trial and error but I suspect it would be around .8v.

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