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Initially a box is displayed with text at the top, and three separate blank spaces below.

The first line of text reads ‘Create a binary data stream’. This is followed by an input box, with the greyed-out text ‘e.g. 1001011’, and next to this a button labelled ‘Submit’.

Below this is the text ‘Select binary modulation scheme:’ and a drop-down menu with the following options: ‘OOK’, ‘ASK’, ‘BFSK’ and ‘BPSK’. This is followed by a sliding scale with the text ‘Carrier frequency:’, which is labelled ‘low’ at the left-hand side and ‘high’ at the right-hand side.

The input box allows a stream of zeros and ones to be typed in. This can be any combination of zeros and ones but must be between one and ten characters in length.

Once the binary stream has been input, the drop-down menu is used to select the required binary modulation scheme.

Pressing the Submit button then generates three waveforms in the three blank spaces below.

All three waveforms have an X axis labelled time, with no units or values indicated, and a Y axis labelled voltage (V).

The first waveform is labelled ‘Data’ and illustrates the binary data stream as a series of voltage levels. The Y axis extends from 0 to 1 and the X axis is segmented into equally spaced sections, where the duration of each segment is associated with one binary data bit. Where the binary data is a ‘one’, a voltage level of ‘one’ is illustrated for the duration of the segment. Where the binary data is a ‘zero’, a voltage level of ‘zero’ is illustrated for the duration of the segment.

The second waveform is labelled ‘Unmodulated carrier’. This is a sine wave and the Y axis extends from plus one to minus one. The segments that correspond to the duration of each of the binary data bits in the first waveform are also indicated on the X axis here. The frequency of the sine wave can be varied by using the sliding scale labelled ‘Carrier frequency’ described previously. With the sliding scale at its lowest value, two full cycles are completed within each bit duration. With the sliding scale at its highest value, ten full cycles are completed within each bit duration.

The third waveform is labelled according to the binary modulation scheme that was selected using the drop-down menu. That is, either ‘On-off keying (OOK)’, ‘Amplitude shift keying (ASK)’, ‘Frequency shift keying (BFSK)’ or ‘Phase shift keying (BPSK)’. This waveform also has the segments that indicate the bit durations marked, and the Y axis extends from plus one to minus one.

If OOK has been selected from the drop-down menu, then where the bit value illustrated in the first waveform is one, the third waveform looks the same as the unmodulated carrier. Where the bit value illustrated in the first waveform is zero, the third waveform is also zero.

If ASK has been selected, then where the bit value illustrated in the first waveform is one, the third waveform looks the same as the unmodulated carrier. Where the bit value illustrated in the first waveform is zero, the third waveform looks like the unmodulated carrier in terms of phase and frequency, but the peak value is smaller – approximately 0.5.

If BFSK has been selected, then where the bit value illustrated in the first waveform is one, the third waveform looks the same as the unmodulated carrier. Where the bit value illustrated in the first waveform is zero, the third waveform looks like the unmodulated carrier in terms of phase and amplitude, but the frequency of the waveform is lower – in fact, it is half the frequency of the carrier.

If BPSK has been selected, then where the bit value illustrated in the first waveform is one, the third waveform looks the same as the unmodulated carrier. Where the bit value illustrated in the first waveform is zero, the third waveform looks like the unmodulated carrier in terms of frequency and amplitude, but the phase of the waveform is different – in fact, it is the unmodulated carrier with a phase shift of pi radians or 180 degrees.

 1.6 Phase-shift keying (PSK)