Signalling

AS Unit G491 - Physics in Action

Chapter 3 - Signalling

Title	Description
Wave on a string	Investigate the oscillations of waves on a string. Complements the work done in the lab. Click here to load.
Task 1 - A History of signalling	Your teacher will explain some of the important milestones in the development of our signalling technology, using this powerpoint presentation to illustrate some ideas. It is also worth looking at this page.
Task 2 - Generating Signals Part I	Following these instructions, use Audacity to generate a range of signals with multiple frequency components and sketch what you see.
Task 3a - Sampling Signals I (Sampling rate)	In order to store a signal on a digital medium (such as a memory stick or computer hard drive) we must first sample the signal (read its value) at regular intervals. What we record will never be as good as the original signal, but if we sample often enough, we should be able to preserve most of the important information. These notes explain a little more about sampling, and also explain some of the problems which can occur if we do not sample a signal often enough, including aliasing and loss of high frequency detail. How often do we need to sample a signal to create an accurate reconstruction? Try this exercise to find out.
Task 3b - Sampling repetitive motion	Your teacher will demonstrate some of the effects which can occur when we do not sample often enough, using a strobe light, desk fan, and a spinning disc. These questions get you to do some number-crunching for the kind of problems you have just seen.
Task 4 - Sampling Signals II (Signal resolution)	The sampling rate determines how often we take a sample, but we also need to consider the resolution used for our measurements of signal value. Your teacher will explain what is meant by signal resolution. You may also find it useful to look at the diagram and notes on this sheet, which explain about quantisation errors. [Teacher note: insert link to , and page references for AS book] Try this activity to see how signal resolution and sampling rate affect the quality of the reproduced signal. You will need graph paper and a sharp pencil. Teacher note: there is a spreadsheet here showing the reproduced signal at each of the specified resolutions and sampling rates.
Task 4b - Sampling exam questions	Suggested exam question(s): June 2010 Q11 (Section B)
Task 5a - numerical analysis of signals
Task 5b - Signalling starter	This powerpoint presentation contains definitions of important key terms, and a starter question using the ideas you have learned about sampling rates and signal resolution.
Sending and Receiving Signals	See how radio waves are transmitted and received by the oscillations of charges and fields in an aerial. Click here to load.
Investigating signalling and audio editing	Use the "audacity" sound editing software and follow these instructions to learn about sampling, sampling frequencies and filters.

Signals as Digital Samples	Digitising A Signal - exercise in sampling and digital conversion. (powerpoint version here for display purposes)
Resolution of a Digital Signal	These summary notes explain how the resolution of a sample affects the quality of a digital signal, and how quantisation errors occur if our samples do not have sufficient resolution.
Data transfer rates	Answer these questions on data transfer times and rates for various types of data and connection.
Different Ways of Looking at a Signal	These summary notes explain the difference between the three main ways of looking at a signal - waveform views, spectral views and frequency spectra.
Sampling repetitive motion	Your teacher will demonstrate some of the effects which can occur when we do not sample often enough, using a strobe light, desk fan, and a spinning disc.
Sampling repetitive motion	These questions get you to do some number-crunching for the kind of problems you have just seen.
Noise in signals	Starter question here.
Noise in Signals	Suggested exam questions: Jan 2010 Q4 (section A, 5 marks) June 2011 Q9 (Section B, 10 marks)
Signal resolution - how many bits for each sample?	Look at this signal - your teacher will explain how each sample can be encoded digitally and show how the signal resolution (number of levels) can affect the signal quality. There is a worksheet for you to complete here.