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I have been using sorcerer and pc-hfdl to successfully decode HFDL I find on SDR receivers but I have recently found a signal that looks and sounds exactly like HFDL but doesn't decode to anything. I know the transmitter is a "foreign military entity". Could it be that there is a secure version of HFDL meant for military use that doesn't decode? Could it be a problem with fonts? Do you know of another HF upper sideband signal that I could be mistaking for HFDL?