The Model 789 SGLS Signal Generator is part of the GDP Space Systems’ Modular Subcarrier System (MSS) family. The MSS family provides high performance Phase Shift Keyed (PSK), Frequency Shift Keyed (FSK), Phase Modulation (PM), Space Ground Link System (SGLS) and Digital Baseband (BB) signal generation. Upconversion can also be added to translate subcarrier frequencies to a 70 MHz output signal. Direct Digital Synthesis (DDS) techniques are used to produce the subcarriers at frequencies up to 10 MHz. The MSS modular architecture utilizes a series of VME based modules which can be readily configured for generation of PSK, FSK, PM, SGLS, and Digital BB signals.

The GDP Space Systems Model 789 SGLS Signal Generator provides multi-channel Space Ground Link System (SGLS) compatible Telemetry Tracking and Command (TT&C) and communication subcarrier signals.

 The model 789 includes three FSK/AM/PM Modulators, two BPSK Modulators, a Ranging Tone Generator, and a Signal Summer/Level Control module. The unit accepts three SGLS dibit encoded data/clock and three auxiliary data/clock inputs for FSK subcarrier modulation; two data and clock inputs for BPSK subcarrier modulation; a ranging signal input for Range Tone output selection; and an external analog input channel. An internal pseudo-random noise (PRN) generator can be selected in place of any of the external data inputs. Signal level control and ON/OFF selection is provided for each Modulator output, the digital baseband ranging signal , and the buffered analog input signal.The Modulator and Range Tone Generator outputs and the external analog signal are routed to the Summer. Up to four-of-seven signals are combined to produce a Composite Output signal. Individual signal level and ON/OFF control is provided for the four selected signals on the Summer, as well as selectable attenuation of the composite output. All selectable functions are controlled through either the local front panel display and keypad, or the IEEE-488 remote control port.