AT-3004D/AT-3104 is a proprietary modem developed by the Russian company AO "Almaz". Its main users are the various fleets of the Russian Navy. It is a generic data modem that can be used with a variety of equipment, including teleprinters and voice encryption units.
The main and most common waveform uses 12 carriers, located every 200 Hz between +700 and +2900 Hz inclusive, plus an extra unmodulated pilot tone at +3300 Hz. Each of the 12 carriers is modulated at 120 Bd using either BPSK or QPSK.
12-carrier AT-3004D/AT-3104 in idle condition
12-carrier AT-3004D/AT-3104 in standby condition, followed by the traffic condition
The newer successor of AT-3004D, AT-3104, is additionaly capable of another waveform, although rarely found in practice, at least on long distance links; it uses 20 carriers, located every 120 Hz between +670 and +2950 Hz inclusive, plus an extra unmodulated pilot tone at +3300 Hz. Each of the 20 carriers is modulated at 75 Bd using either BPSK or QPSK.
20-carrier AT-3104 in traffic condition
According to the manufacturer, the supported net data rates are 1200 and 2400 bit/s, likely corresponding to the use of BPSK and QPSK respectively.