The PDM001 Sub-Carrier Demodulator performs coherent demodulation of Binary Phase Shift Keyed (BPSK) and optionally Quadrature Phase Shift Keyed (QPSK) sub-carriers. The input subcarrier frequency range is from 1 kHz to 10 MHz. One of Four input connection points is program selectable (two each on the edge panel and P2 connector) to be applied to the demodulator. Input impedance is selectable to be either 50Ω (optional 75Ω)] or 10KΩ. Band-pass filtering of the input signal is accomplished by programming the cutoff points of Sub-Carrier High-Pass and Low-Pass Bessel filters. The filters attenuate adjacent sub-carriers allowing the PDM001 to operate with wide-band input signals containing many sub-carriers. The high and low-pass filters are independently bypassed if desired.

The PDM001 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 Bessel filtered to provide the data and phase error indications. 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 30 dB of dynamic range allowing the user to handle a 50 mVp-p signal as well as a TTL BPSK modulated signal (5 Vp-p).

The PDM001 operates under software control via the VME bus. The module utilizes eight 16-bit registers to contain all operational control parameters to govern the PDM001. Two status read-back registers contain all information needed to monitor the operation of the demodulator.