Standard Frequencies
WWV and WWVH transmit 44 seconds of audio tone in most minutes. It begins after the 1-second minute mark and continues until the beginning of the WWVH time announcement 45 seconds after the minute.
Even minutes (except for minute 2) transmit 500 Hz, while 600 Hz is heard during odd minutes. The tone is interrupted for 40 ms each second by the second ticks. WWVH is similar, but exchanges the two tones: 600 Hz during even minutes and 500 Hz during odd.
WWV also transmits a 440 Hz tone, a pitch commonly used in music (A440, the note A above middle C) during minute :02 of each hour, except for the first hour of the UTC day. Since the 440 Hz tone is only transmitted once per hour, many chart recorders may use this tone to mark off each hour of the day, and likewise, the omission of the 440 Hz tone once per day can be used to mark off each twenty-four hour period. WWVH transmits the same tone during minute :01 of each hour.
No tone is transmitted during voice announcements from either WWV or WWVH; the latter causes WWV to transmit no tone during minutes :43–:51 (inclusive) and minutes :29 and :59 of each hour. Likewise, WWVH transmits no tone during minutes :00, :30, :08–:10 and :14–:19.
Audio tones and other voice announcements are sent at 50% modulation.
Read more about this topic: WWV (radio Station), Broadcast Format
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