WWVB Subcode Test Generator - wwvb1.exe



NIST LF radio station WWVB transmits the official US time with a 1 Hz AM subcode on a 60 kHz carrier. This is the signal received by self-setting atomic time radio controlled clocks and watches you may have seen in recent years.

The data rate is one bit per second, or 1 baud. The signal format is well documented and both consumer electronics companies and home experimenters have built LF receivers and subcode processors to extract the bits from the signal and convert them to standard date and time formats. 

However, the reverse is also possible. Knowing the current date and time it is simple to predict what the bits will look like. Below is a Windows command line tool which predicts and displays the subcode.


Based on the current time of your PC, the program calculates what the WWVB subcode looks like at this minute and for as many minutes in the future you care to view. The subcode is displayed it in the typical WWVB capture format of 0's, 1's, and 2's.

Here is a sample output:

Output Format

The columns on the left are the year ('05, short for 2005), the day of year (today is the 38th day of 2005), the UTC hour and minute. The string of 60± digits on the right are the subcode that WWVB will send in the next minute. By default ten minutes of subcode is displayed. A '0' represents a binary zero, which is transmitted by a 200 ms pulse of reduced power. A '1' represents a binary one,  which is transmitted by a 500 ms pulse of reduced power. Finally, a '2' represents a position marker, which is transmitted by an 800 ms pulse of reduced power. There is one pulse per second.

As with most command line utilities, the output may be redirected to a file.


You can find the Win32 binary and source code in my tools directory:

See also

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