This lecture covered a number of aspects of analogue and digital technology. Looking at the various types of signals and the corresponding data types that can be transmitted using the various signal types:
| Analogue Data | Digital Data | |
|---|---|---|
| Analogue Signal | Radio, TV | Fax Machines |
| Digital Signal | Mobile Phones | Computers |
The difference between the two types of signal and the different data types transmitted using each signal was shown.
An analogue signal is naturally varying over a certain range, within that specific range there are an infinite number of values that the analogue signal will represent at any one point. A classic example that is used to distinguish between analogue and digital is a dimmer switch that is used to turn on a light. The dimmer switch can be moved to any point around its circumference, and at any one point between the 360 degrees that the switch may turn the light will be varied at that level. This is in contrast to a regular light switch that can only be turned on or off.
This is fundamental to the understanding of a digital signal. A digital signal is represented electronically as either a ‘1’ or a ‘0’, an electrical pulse or no electrical pulse, a pulse of light, or no pulse of light, ‘on’ or ‘off’ in the light analogy respectively.
Analogue signals can transmit analogue data, this is experienced in our every day lives as television, radio, everything we hear and see is also in analogue and can be considered as analogue data. An analogue signal can transmit digital data such as used in a fax machine.
Broadband technology such as ADSL (Asymmetric DSL) is an example of an analogue signal being used to transmit digital data, as is the case with communications using a normal modem. A regular modem will simply convert a digital signal to an analogue signal and vice versa most modems offer data transfer rates of 56kbps. ADSL has the capability of offering 8mbps downstream data transfer and 1mbps upstream data transfer compared to 56kpbs. The only difference however is to use ADSL the user requires a specific ADSL modem, a splitter which removes voice from data, and an Ethernet card which creates a short two node network between the computer and the ADSL modem, but providing high speed communication between the two.
In terms of signals and data transmission, for effective communication there are very specific requirements, and environmental constraints; providing these are satisfied analogue can be an effective method for data transmission. However it can be prone to errors, digital provides an alternative.
Digital signals can transmit digital data, and analogue data. Digital data refers to the way data moves around circuits within computers and other such devices such as the internal workings of a video recorder, mobile phone, or even microwaves. The binary values of zero or one are converted to pulses of electricity and pass along circuits this way. At the other side of the circuit it is converted back into its binary representation.
Analogue data can also be sent using a digital signal. The mobile phone provides us with an example. Within a mobile phone the analogue voice signal is converted into binary, binary is then converted to an undulating current and sent as pulses along analogue circuits. These pulses are sent over 823 microwave frequency channels divided into four dedicated categories for control, paging, access and data. When the signal arrives at its destination is converted back into binary, and then back into its corresponding analogue signal. The mobile phone used to use analogue signals to represent the voice signal, but applying digital technology now allows for the transmission of digital voice data, and digital voice and data, represented as third generation technology (3G).
The advantage of converting the analogue voice signal to digital is that any distortion introduced into the signal during transmission can be located and removed at any point, usually at the destination mobile, this allows the user on the other end of the mobile to receive a full quality communications transmission. This is called error correction and is one of the many advantages of using digital signals to transmit analogue signals. It is not possible to achieve this within the analogue signals used to transmit analogue data.
The lecture also looked at the spectrum of signals and the concept of bandwidth of a particular type of wave. Hand-shaking protocols were also covered, which allow analogue communications methods to achieve the highest communications rate possible.
Digital signals, for analogue and digital data transmission does have its advantages. But it also has its disadvantages, such as the frequencies that are removed using the mp3 encoding process to reduce the size of a sound recording, this would not be possible with an analogue recording, and it is be debatable which would provide the better quality playback. Also the ability to receive an analogue signal is relatively easy as was shown with an old record and needle, and a basic crystal radio, not even accurate documentation of digital circuitry, and architecture could allow for a layman to pick up the blue print for a digital radio box and recreate one, technological expertise would be needed to create the circuits, and to even understand the plans. Therefore the question must be asked how much should one rely on digital wizardry? Unfortunately the answer may not be provided until one day we are forced to find out.
References
www.ieee-virtual-museum.org - accessed 28th January 2005
www.webopaedia.org - accessed 28th January 2005
www.marconicalling.com - accessed 28th January 2005
Bibliography
Brookshear, J. G. (2000). Computer Science, An Overview. Addison-Wesley
Tanenbaum, A, S. (1996). Computer Networks. Prentice-Hall