26-11-2012, 06:12 PM
Binary phase shift keying
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Preliminary discussion
Experiments 15 and 16 show that the AM and FM modulation schemes can be used to transmit
digital signals and this allows for the channel to be shared. As digital data forms the message
instead of speech and music, it is preferred that these two systems are called ASK and FSK
instead.
Recall that ASK uses the digital data’s 1s and 0s to switch a carrier between two amplitudes.
FSK uses the 1s and 0s to switch a carrier between two frequencies. An alternative to these
two methods is to use the data stream’s 1s and 0s to switch the carrier between two phases.
This is called Binary Phase Shift Keying (BPSK). Figure 1 below shows what a BPSK signal looks
like time-coincident with the digital signal that has been used to generate it.
Procedure
Part A – Generating a BPSK signal
A BPSK signal will be generated by implementing its mathematical model. For more information
on this, refer to the preliminary discussion of Experiment 5.
1. Gather a set of the equipment listed above.
2. Set up the scope per the instructions in Experiment 1.
3. Set the scope’s Trigger Source control to the EXT position.
4. Set the scope’s Trigger Source Coupling control to the HF REJ position.
5. Set the scope’s Channel 1 and Channel 2 Input Coupling controls to the DC position.
6. Set the scope’s Timebase control to the 0.1ms/div position.
7. Locate the Sequence Generator module and set its dip-switches to 00.
Tip: To do this, push both switches up.
8. Connect the set-up shown in Figure 2 on the next page.