The Model 742 Sub-Carrier Demodulator performs coherent demodulation of Binary Phase Shift Keyed (BPSK) and optionally, Quadrature Phase Shift Keyed (QPSK) sub-carriers. The input sub-carrier frequency range is from 1 kHz to 10 MHz. Four input connections are provided from which, one is program selected to be applied to the demodulator. The input impedance is selectable to be either 50W (optional 75W) or 10KW. Band-pass filtering of the input signal is accomplished by programming the cutoff points of a Sub-Carrier High-Pass and a Low-Pass filter. The filters attenuate adjacent sub-carriers allowing the model 742 to operate with wide-band input signals containing many sub-carriers.
The high and low-pass filters are independently bypassed if desired.
The Model 742 employs a Costas Loop to achieve coherent carrier recovery and automatic gain control (AGC). The input signal is multiplied by the sine and cosine of a local oscillator (NCO) resulting in a spectrum that is filtered to provide the data and phase error indication. The data and phase error channels are sampled, converted to equivalent digital values and subsequently processed by a Digital Phase Lock Loop (DPLL), a Digital Sync Detector (DSD) and a Digital AGC circuit. Phase differences between the input sub-carrier and the NCO are corrected by the DPLL while the DSD detects carrier phase synchronization and provides lock status. The Digital AGC circuit produces a wide dynamic range of more than 30dB.
• BPSK (QPSK Optional)
• Tunable Sub-carrier – 1 kHz to 10 MHz
• Tunable Data Bandwidth – 1 kHz to 10 MHz
• Tunable Sub-Carrier Filtering – 1 kHz to 10 MHz
• Tunable Loop Bandwidth – 1 Hz to 32 kHz
• Four Input Connections
• Selectable Input Impedance – Low = 50 Ohms and High = 10k Ohms
• Status Indications – Loss of signal, Sub-carrier Synchronization and Digital Loop Deviation
• Remote Control – RS-232 and IEEE-488