Increasing the Modulation Depth of the WWVB Time Code to Improve the Performance of Radio Controlled Clocks

The National Institute of Standards and Technology radio station WWVB has officially changed its broadcast format. As of January 1, 2006 the WWVB broadcast signal has increased the depth of the time code modulation from 10 dB to 17 dB. The increase in modulation depth has been implemented to improve the performance of commercial radio controlled clocks in areas of low signal strength. The increase in modulation depth effectively appears to a matched-filter receiver as if the transmitted power has increased by 2.0 dB, thus extending the coverage area over which WWVB controlled clocks will work properly. This is demonstrated by an amplitude shift keyed (ASK) analysis. The results given by this analysis do not depend on the noise level or the bit error rate (BER)