AT-3104 is a proprietary HF modem, used primarily by the Russian Navy. It is the successor to the earlier AT-3004D.
AT-3104 is one of the traffic modes available for ship-to-shore links. When link setup is coordinated using Morse code, it is referred to as "QYT4."
AT-3004D and AT-3104 are nearly always seen transmitting using the 12-carrier PSK waveform. The supported data rates are 1200 bit/s (using BPSK) and 2400 bit/s (using QPSK). It has three identifiable conditions:
AT-3104 introduced an additional 20-carrier PSK waveform. However, it is very rarely used in practice.
Recording courtesy of Radioscanner