COM-1002 BPSK/QPSK/OQPSK modulator 
-> COM-4004 70 MHz IF modulator
-> 40 dB attenuator 
-> COM-3004 20-90 MHz IF receiver
-> COM-1008 Variable decimation 
-> COM-1001 BPSK/QPSK/OQPSK demodulator
-> COM-1005 BER measurement


Purpose:
Demonstrate the transmission of a 39.0625 Kbit/s BPSK modulated data stream at 25 MHz 
intermediate frequency. Test conditions: noiseless channel, internal clock references.
The receiver variable decimation module is set to reduce the sampling rate from 40 Msamples/s
down to 312.5 Ksamples/s. Given the -3 dB filter bandwidth of 12.6% of the output sampling
rate, the COM-1008 variable decimation has an equivalent bandwidth of 39.3 KHz (may create some 
intersymbol interference as it is somewhat close to the 39.0625 KHz modulation bandwidth, 
but good at rejecting noise and preventing aliasing). The BPSK demodulator is configured
with extended frequency acquisition, as the internal clock references within the COM-4004 
and COM-3004 analog modules may create 100ppm of frequency error (100ppm @ 25 MHz = 2.5 KHz, 
greater than the 400 Hz digital costas loop acquisition range). 


(a) assemble the ComBlock modules listed above. 
Insert an RF attenuator (40 will work) between the transmitter assembly
and the receiver assembly.
Connect a serial link between a host PC and the COM-1002 module.
Power up the assemblies.
Using the ComBlock control center, enumerate the ComBlocks (2nd button to the left), 
then import (Menu File | Import) the transmitter settings file 1002_4004_3004_1008_1001_1005_tx.stn

(b) move the serial link to the COM-3004 module.
Using the ComBlock control center, enumerate the ComBlocks (2nd button to the left), 
then import (Menu File | Import) the receiver settings file 1002_4004_3004_1008_1001_1005_rx.stn
Both assemblies are now configured. Switch the power supply off then on again.


(c) check the receive baseband signals using an oscilloscope at the COM-3004 receiver. 
  The I/Q baseband signals can be visualized at the COM-3004 receivers at test points
  TP3 (I-channel) and TP4 (Q-channel).
  When the receiver AGC is working properly, the received I and Q baseband signals should be
  1Vpp, filtered (no sharp transition) bit streams. Because of carrier phase offset between 
  transmitter and receiver, the received baseband signals are phase rotated versions of the
  transmitted baseband signals.

(d) Verify demodulator lock:
at the COM-1001 demodulator: 
  - TP1 is high when the carrier tracking loop is locked
at the COM-1005 BER measurement: 
  - TP1 is high when the module is synchronized with the PRBS-11
  - TP3 is low (no bit error)
  - TP4 consists of periodic pulses every 2047 bits (52.4 ms).

Given the slow data rate, it takes about 20 seconds for the extended acquisition mechanism
to lock.  

(e) Compare the transmitted bits and received bits: 
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 BPSK phase ambiguity. 

(f) 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.