COM-1028 FSK/MSK/GFSK/GMSK digital modulator
 -> COM-4004 70 MHz IF modulator and frequency synthesizer
    -> 20-40 dB attenuator
      -> COM-3004 IF receiver [20 - 90 MHz], frequency synthesizer, AGC, A/D conversion, -B wideband
        -> COM-1027 FSK demodulator, up to 10 Msymbols/s.
          -> COM-1005 BER measurement


Objective:
Test an end-to-end GFSK modulated channel at an intermediate frequency of 70 MHz.
A pseudo-random PRBS-11 sequence is transmitted at 1.248 Mbit/s. 
After demodulation, the BER is measured to be zero.


a) Connect a serial cable between the host computer and the COM-1028 modulator.
Using the ComBlock Control Center software File | Import menu, 
import the 1028_4004_3004_1027_1005_tx.stn test script into the modulator assembly.

b) Connect a serial cable between the host computer and the COM-3004 receiver.
Using the ComBlock Control Center software File | Import menu, 
import the 1028_4004_3004_1027_1005_rx.stn test script into the demodulator assembly.

c) Using an oscilloscope, check COM-3004 baseband test points TP3/TP4 (just prior to 
A/D conversion).
Check the GFSK baseband waveform. Each data bit is associated with 
a +/- pi/2 change in phase. Verify that the AGC loop maintains the baseband signal
amplitude to approximately 1V peak-to-peak.

d) Using the ComScope feature of the ComBlock Control Center, plot the 
digitized I/Q inputs. To start Comscope, highlight the COM-1027 FSK demodulator in 
the main window and click on the fifth button. 
Select trace 1 | signal 1 | 8-bit unsigned format | 1:4 decimation | line plot style
Select trace 2 | signal 1 | 8-bit unsigned format | 1:4 decimation | line plot style
Apply changes, re-arm trigger and force trigger.
The signals should look like the GFSK modulated baseband signals seen at step c).

e) Reset the COM-1005 BER counter by applying value 2C in the only control register.
Monitor the cumulative BER:
REG6/7/8/9 represent the total number of errors
REG10/11/12/13 represent the total number of bits received.
One can let it run until the total number of bits reaches FFFFFFFF = 4.29 billion bits.
In the absence of external interferers, the cumulative BER should be zero since the
channel is noiseless.