QPSK modulator COM-1002 -> AWGN generator COM-1023 -> QPSK demodulator COM-1001 -> BER measurement COM-1005. Test configuration example: - 19.8 Mbit/s QPSK non-differential - no frequency error - 6.2 dB Eb/No Back to back digital modem operations in an additive white noise environment can be verified at baseband. The QPSK modulator is configured in signal generator test mode whereby a periodic 2047-bit sequence is being transmitted. A precise digital noise generator (COM-1023) is used to add white gaussian noise. The end to end BER is measured using the COM-1005 module. Proper operation can be verified as follows: (a) import the 1002_1023_1001_1005_1.stn settings into the assembly, using the ComBlock Control Center file | import menu. (b) 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 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 bit errors, processing delay and inversions due to QPSK phase ambiguity. (c) from the ComBlock control center check the BER (COM-1005 status). It will show bit errors of approximately 0x001200 = 4608 errors per million = 4.6 10-3.