GBZ is the callsign of a British VLF transmitter, which transmits on 19.6 kHz from Anthorn (formerly Criggion) encoded signals to submarines. Although the signals of GBZ cannot be decoded by common means, its reception - if its signal is shown in form of spectrograms - is very interesting, because the signals of GBZ show figures looking like fishes, garlands and ornaments on the spectrograms. At certain times these signals are also transmitted as strong pulses, so-called superpulses, which can oversteer the amplifier of a PC soundcard at distances of a hundred kilometres away from transmission site.
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