High Frequency (HF) - preppernet.com · Crest Trough Crest Callsign Groups All valid US Callsigns...
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High Frequency (HF) - preppernet.com · Crest Trough Crest Callsign Groups All valid US Callsigns start with A, K, N or W and contain a digit 0-9 Group A Group B Group C Group D Ix2,
