Observations were made of the radio noise background in the frequency range 150–180 kHz to provide reference data for the design of the ground wave emergency network system. These observations were undertaken at Nanjemoy, Maryland, during early summer 1983 and included 41 days of data recording. The noise environment was found to be dominated by impulsive thunderstorm noise. A typical nighttime mean noise power spectral density was 1×10−15 W m−2 Hz−1 (noise factor of 107 dB above kT0), while a typical daytime level was at least 14 dB quieter. However, the daytime level was at times significantly higher, especially during the presence of a local thunderstorm front. During local thunderstorm activity, impulses with peak power spectral density of 1×10−14 W m−2 Hz−1 were observed frequently, while the most energetic pulse detected during our monitoring period had a peak power spectral density of 6.8×10−14 W m−2 Hz−1 (Fa = 125 dB). Sample amplitude probability distributions and time probability distributions are presented for day/quiet, night, and thunderstorm conditions. Agreement with the mean noise level predictions of CCIR report 322 is satisfactory within the accuracy limits of the CCIR data.
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