AT-3004D is a proprietary modem developed by the Russian company AO "Almaz" in the 1980s. It is widely deployed in many Russian military settings, and very frequently found on HF radio. 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 200Hz between +700Hz and +2900Hz inclusive, plus an extra unmodulated pilot tone at +3300Hz. Each of the 12 carriers is modulated at 120Bd 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 used in practice; it uses 20 carriers, located every 120Hz between +670Hz and +2950Hz inclusive, plus an extra unmodulated pilot tone at +3300Hz. Each of the 20 carriers is modulated at 75Bd using either BPSK or QPSK.
20-carrier AT-3104 in traffic condition
According to the manufacturer's description, the supported net data rates are 1200 and 2400 bit/s, likely corresponding to the use of BPSK and QPSK respectively.