{'fraction_non_alphanumeric': 0.02577319587628866, 'fraction_numerical': 0.0, 'mean_word_length': 5.202127659574468, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Mitigation of time-varying spectral nulls in a wideband HF signal

Multiple and time-varying spectral nulls have been observed in wideband HF-NVIS channel. These nulls cause rapid fading in narrowband HF-NVIS links. This paper offers one physical explanation of these observations — the rapid fading is caused by interference between the ordinary (O mode) and extraordinary (X mode) waves carrying the signal in opposite sense polarization at the receiver. This explanation points to a mitigation scheme: coherently combine dual-polarization receive antennas to eliminate the nulls.