Receivers/Demodulators & Downlink: RF, IF & Sub-Carrier

Model 742 PSK/QPSK Subcarrier Demodulator (2U Chassis)
Model 742

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 50 Ohm (optional 75 Ohm) or 10K Ohm. 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.

  1. BPSK (QPSK Optional)
  2. Tunable Sub-carrier
  3.      • 1 kHz to 10 MHz
  4. Tunable Data Bandwidth
  5.      • 1 kHz to 10 MHz
  6. Tunable Sub-Carrier Filtering
  7.      • 1 kHz to 10 MHz
  8. Tunable Loop Bandwidth
  9.      • 1 Hz to 32 kHz
  10. Four Input Connections
  11. Selectable Input Impedance
  12.      • Low = 50 Ohms
         • High = 10K Ohms
  13. Status Indications
  14.      • Loss of signal
         • Sub-carrier Synchronization
         • Digital Loop Deviation
  15. Remote Control
  16.      • RS-232
         • IEEE-488


BPSK and QPSK Option
Input Sources:
Input Impedance Selection:
50 Ohm (optional 75 Ohm); 10K Ohm
Input Amplitude Dynamic Range:

30dB (-15 dBm to +15 dBm std. Other ranges optional)
Sub-Carrier Frequency Range:

1 kHz to 10 MHz
Sub-Carrier Tuning Resolution:

32 bits
Sub-Carrier Accuracy:
50 ppm std.; 10 ppm optional
Sub-Carrier High Pass Filter Cut-Off Frequency:

1 kHz to 1 MHz or Bypass
Sub-Carrier Low Pass Filter Cut-Off Frequency:

10kHz to 10MHz or Bypass
Data Bandwidth:
Bessel Characteristics Double Sided Bandwidth (-3dB) 1 kHz to 10 MHz
Loop Bandwidth:
1 to 32767 Hz Damping factor 0.707
Carrier Tracking:
2 times LBW setting
6 dB Eb/No to maintain reliable phase lock
Implementation Loss:
0.5 dB

Data (I & Q):
0.5 Vpp into 50 Ohms
Local Oscillator:
0.5 Vpp into 50 Ohms

Status Indications:
Signal Loss, Sub-Carrier Lock, Loop Deviation

Remote Control:
RS-232, IEEE-488