Turbo code encoder COM-7001 
-> QPSK modulator COM-1002 
-> COM-4001 dual-band 915MHz/2.4GHz quadrature modulator
-> 20 - 30 dB attenuator 
-> COM-3001 dual-band 915 MHz / 2.4 GHz receiver 
-> QPSK demodulator COM-1001 
-> Turbo code decoder COM-7001 
-> BER measurement COM-1005.

Important note: this setup requires that an external 40 MHz clock be provided to the 
COM7001 at the input J2/ pin A1.


Test configuration example: 4 Mbit/s QPSK, 850 MHz RF center frequency, external clock


The turbo-code encoder is placed in signal generator test mode, 
whereby a periodic 2047-bit sequence (PRBS-11) is being transmitted. 
The resulting data stream is FEC encoded, QPSK modulated, QPSK demodulated, FEC decoded. 
The end to end BER is measured using the COM-1005 module. 

Proper operation can be verified as follows:

(a) assemble the ComBlock modules listed above. 
Insert an RF attenuator (20 to 30 dB will work) between the transmitter assembly
and the receiver assembly.
Connect a serial link between a host PC and the COM-7001 turbo-code encoder module.
Connect an external 10 MHz frequency reference to the EXT_CLK port of the COM-4001 module.
Connect an external 10 MHz frequency reference to the EXT_CLK port of the COM-3001 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 7001_1002_2001_4001_3001_1001_7001_1005_tx.stn

(b) move the serial link to the COM-3001 module.
Using the ComBlock control center, enumerate the ComBlocks (2nd button to the left), 
then import (Menu File | Import) the receiver settings file 7001_1002_2001_4001_3001_1001_7001_1005_rx.stn
Both assemblies are now configured. Switch the power supply off then on again.

(c) verify that the RF frequency synthesizers are locked:
at the COM-4001 modulator: SYNC_LOCK is low, PLL_REF is a 10 MHz clock
at the COM-3001 receiver: PLL_LOC is low, PLL_REF is a 10 MHz clock.

(d) check the baseband signals using an oscilloscope. 
- At the COM-2001 dual D/A converter: probe at the capacitors C3 and C24 near the output SMA connectors.
  The signals should be 1Vpp, filtered (no sharp transition), bit streams. The I-channel is near C3, 
  the Q-channel at C24. 

- At the COM-3001 receiver. 
  The same baseband signals can be visualized at the COM-3001 receivers at test points
  TP1 (I-channel) and TP2 (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.

(e) Verify demodulator lock:
at the COM-1001 demodulator: 
  - TP1 is high when the carrier tracking loop is locked

(f) COM-7001 decoder  TP4 shows periodic start of frame pulses every Turbo-code block 
(4096 bits + 32 bit unique word = 1.032ms @ 4 Mbit/s). 

COM-7001 decoder TP2 D_GOUT shows how much decoding capacity is used in the Turbo code 
decoder for this configuration (4 Mbit/s, 0.793 code rate, 6 decoding iterations). 
The duty cycle indicates the available capacity (low indicates Turbo code decoder is busy). 

(g) At the BER measurement, verify that 
- COM-1005 TP1 is high, indicating synchronization with the 2047-bit periodic test pattern 
- COM-1005 TP3 is low, showing no bit error pulse.


(h) 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.