Waveform Comparisons
Start of next second
in time code
ON-TIME 1 PPS
REFERENCE
REFERENCE
IRIG ZERO
IRIG ONE
Modulated
Unmodulated
Figure 23: 1 PPS & IRIG-B Waveforms
Figure 23 illustrates two of the common methods of transmit-
ting IRIG-B, plus one pulse per second (1PPS). Unmodulated is
a square wave string of 100 bits and modulated is a 1 kHz carrier
amplitude modulated with the same number of bits.
Notice that there are three different bit widths: 8 milliseconds,
5 milliseconds and 2 milliseconds. The 8 millisecond pulse is con-
sidered a reference bit, the 5 millisecond pulse is a digital one and
the 2 millisecond pulse width is a digital zero.
Also, notice that the 1 kHz sine wave amplitude follows the
same time frame and pattern as the digital (unmodulated) signal.
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Summary of Contents for 940A
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