QPSK modulator COM-1002 ->  BER/AWGN generator COM-1023 -> Dual D/A conversion (baseband) COM-2001

The COM-1002 generates a QPSK-modulated PRBS-11 pseudo random data stream at 19.8 Mbit/s.
that is 9.9 Msymbols/s. Additive white gaussian noise is added by the COM-1023 module. 
The COM-2001 then converts both In-phase (I) and Quadrature (Q) channels
from 10-bit precision digital to 1Vpp analog.

(a) Import the 1002_1023_2001.stn settings into the assembly.

(b) using an oscilloscope, check the COM-2001 outputs. Each channel consists of a filtered 
digital signal. 
Verify that the amplitude is approximately 1V peak-to-peak.
Verify that the baseband signal does not contain any glitch or sudden transition.
Verify that the symbol rate is 9.9 MSymbols/s.

(c) using a spectrum analyzer, check the COM-2001 outputs.
The output is a QPSK modulated signal centered at zero frequency.

(d) read the noise power and signal power prior to scaling:
- Noise power prior to scaling is typically x022000 as read 
from the COM-1023 monitoring registers REG17/18/19
- Signal power is typically x07C4B0 as read from the COM-1023
monitoring registers REG14/15/16.

To create a 10 dB SNR in the modulation bandwidth, 
set the noise gain to 

Computation explanation: 
(1) the ratio of signal to noise power prior to scaling is 
0x7C4b0/0x022000 = 3.656 (linear) = 5.62 dB

(2) the signal power density is spread almost uniformly over 9.9 MHz
whereas the noise power is spread almost uniformly over 40 MHz.
Thus, the SNR within the modulation bandwidth prior to scaling is 
5.62 + 10*log10(40/9.9) = 11.68 dB.

(3) therefore, to create a 10 dB in-band SNR, the scaling factors ratio
in amplitude is such that 
(signal amplitude scaling Gs)/(noise amplitude scaling Gn) = 10 dB - 11.68 = -1.68 dB.
In addition, care must be taken not to create overflow conditions.
Let us select
Gs (REG4) = 0x15  signal gain = scaled down to prevent overflow
Gn (REG5) = 0x1A  noise gain

Practical verification:
Set REG4 to 0x15
Set REG5 to 0x1A
Connect spectrum analyzer to one of the COM-2001 output SMA connector.
Verify that the SNR in-band is about 10 dB.

Using an oscilloscope, verify that no overflow occurs at test points TP7,TP8.
Rare overflow can happen at test point TP9.