QPSK modulator COM-1002 -> QPSK demodulator COM-1001 -> BER measurement COM-1005. Test configuration example: 19.8 Mbit/s, QPSK, no frequency error, noiseless. Back to back digital modem operations can be verified at baseband. The QPSK modulator is configured in signal generator test mode whereby a periodic 2047-bit sequence is being transmitted. The end to end BER is measured using the COM-1005 module. The registers settings in the 1002_1001_1005.stn text file. Proper operation can be verified as follows: (a) using an oscilloscope probe: COM-1001 TP1 is high, indicating demodulator carrier lock COM-1005 TP1 is high, indicating synchronization with the 2047-bit periodic test pattern COM-1005 TP3 is low, showing no bit error pulse COM-1005 TP4 shows regular periodic start of frame pulses every 2*2047 bits = 206.76 us. Trigger on COM-1005 TP4, and compare demodulated bits (COM-1005 TP5/TP6) with the transmitted bits (COM-1002 TP2/TP3). The bits should be identical, taking into account processing delay and inversions due to QPSK phase ambiguity. (b) from the ComBlock control center check the BER (COM-1005 status). It will show no bit errors (REG 1 through 4) and the synchronization bit (REG5 bit0) is high.