Re: How DCC signal is superimposed onto AC voltage

Vollrath, Don <dvollrath@...>

Quite simple in theory. There are many means to modulate one signal with another, but for DCC the frequency (or period) of each cycle of AC is changed between two different frequencies to represent a binary one or zero. This is a form of integral cycle frequency shift keying. For DCC the carrier is a flat-topped rectangular AC rather than sinusoidal.
The detection means simply looks for the zero crossings and measures the time between them to determine if a one or zero is being transmitted.
The DCC communication protocol (the particular language of ones and zeroes) is spelled out in the details found at

-----Original Message-----
From: WiringForDCC@...
[mailto:WiringForDCC@...]On Behalf Of Aaron Lau
Sent: Monday, December 12, 2005 6:30 AM
To: WiringForDCC@...
Subject: [WiringForDCC] How DCC signal is superimposed onto AC voltage


Can someone explain to me how signal can be superimposed onto a AC
voltage? I tried finding websites to explain it in technical term, but
to no avail.

Generally, I can't picture how this can happen, needless to say how to
decode it.

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