Talk:Coded mark inversion

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Telecommunications (Rated Stub-class, Low-importance)
WikiProject icon This article is within the scope of WikiProject Telecommunications, a collaborative effort to improve the coverage of Telecommunications on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Stub-Class article Stub  This article has been rated as Stub-Class on the project's quality scale.
 Low  This article has been rated as Low-importance on the project's importance scale.
 

Image is wrong?[edit]

Isn't the second clock level at the wrong level? If a "one" mantains the level and the previous level is found at a top level, it should mantain the level at top level. If not, shouldn't the forth clock level be at low level?

Yes, it looks weird to me, also. But it is entirely consistent with the description given on this page. The first "1" data bit is always a constant Lo level, the second "1" bit is always a constant Hi level, the third "1" bit is a constant Lo level, the fourth "1" bit is a constant Hi level, etc. -- without regard to any intervening "0" bits. --68.0.124.33 (talk) 03:33, 17 July 2008 (UTC)
A better (smaller bandwidth at same data rate, while still forcing a transition at least once every 2 bit times to help clock recovery) but more complex method would be:
  • 0: hold previous level for 1/2 bit time, then switch to other level.
  • 1: if previous bit was 1, then transition at the beginning of the bit time, then hold constant for entire bit time. If previous bit was 0, then hold that previous level for the entire bit time.
This makes the minimum distance between edges 1 bit time (better than the 1/2 bit time currently described in the article), and the maximum distance between edges 2 bit times. (The only other distance between 2 edges that this "better" method allows is 3/2 bit times).
Is there a name for this "better" method? Or is this "better" method, as the above poster suggests, really what is already used in CMI hardware, and the "inferior" method currently illustrated in the article (that occasionally produces short 1/2 bit time pulses) merely an incorrect understanding? --68.0.124.33 (talk) 19:40, 6 October 2008 (UTC)
Stop. This discussion is not intended to create new encoding schemes. —Preceding unsigned comment added by 82.210.249.81 (talk) 07:59, 17 October 2008 (UTC)
Agreed. But if you want to know, it's called Miller encoding or Modified Frequency Modulation. 71.41.210.146 (talk) 11:32, 27 October 2008 (UTC)
Thank you. Yes, the Miller encoding and Modified Frequency Modulation articles are exactly what I was looking for. --68.0.124.33 (talk) 04:09, 13 January 2009 (UTC)

I too think the fase changes are wrong. Besides, the drawing could do with some extra clearification; at least add '1' and '0'. Is there someone with access to the ITU specifications? —Preceding unsigned comment added by 82.210.249.81 (talk) 08:08, 17 October 2008 (UTC)