Model 786 contains the facilities to generate a subcarrier modulated with data received via the RS232 Remote Control, direct TTL serial data and clock inputs from the rear panel, or from the internal pseudo-random or fixed data pattern generators. The modulator is capable of applying any of the standard IRIG codes to the data prior to using it as the modulation stimulus. Modulation types are BPSK and QPSK.

Data received via the RS232 interface is placed into a First-In-First-Out (FIFO) memory buffer. Modulation of the subcarrier with this data is initiated either automatically or by the issuance of a start command (Burst Mode). In between bursts of data a user specified idle data sequence is applied to the subcarrier. Additional start commands can be issued to retransmit a data sequence stored in the FIFO. TTL external data and clock can also be selected by the user as the modulation source. This information is applied directly to the modulation input of the subcarrier generator. It is not stored in the FIFO. A third data source is a pattern generator located on the modulator subcarrier generator. It can generate a 215 -1 PRN pattern; or a continuously repeated fixed word pattern: 1100, 0111, 1010, 1000, 1111, or 0000. The selected data may be passed on to the bit code converter that can decode and / or encode data in NRZ-L/M/S, BiPhase-L/ M/L or DM-M/S.