[drmpeg]

It is incorrect. As you state, a video/audio channel and a DOCSIS channel would look the same on a spectrum analyzer.

Here's a sweep of all the channels (from 80 to 750 MHz) on my Comcast system. This was taken back in 2014, and there were still three NTSC channels (two of which were just a black frame and silence).

https://www.w6rz.net/span.png

A zoom of the last channel at 729 MHz.

https://www.w6rz.net/last.png

MPEG-2 Transport Streams are used for DOCSIS because it's baked into the QAM specification. It's built around 188 byte packets that start with 0x47.

https://wagtail-prod-storage.s3.amazonaws.com/documents/ANSI...