Digital Signal
An example of a digital signal can be seen below. A digital signal works on similar functions to that of the binary number system used in computers. It has two basic ranges unlike the analogue, 0 and 1. The benefits of digital signals can be quite extensive so it’s interesting to look at a couple. Digital is the new up and coming form of communications, especially when it comes to television. It appears to be the new thing and whilst analogue appears to take a back seat the digital era continues to grow. Digital data is not only easily compressed but has further security values involved. Encryption is used widely throughout and enables the signal to not be tampered with by any other outside source. With this in mind when sent as a secured, compacted, source it’s clear to see that more data will be sent with a lot less interference. This is all a computerized process and once again has benefits to it. The computer equipment used in the process is distinctly more reliable than that of its analogue counterpart. The biggest negative though is the fact that analog has been around for some years now and with any new system there needs to be a conversion period. This is likely to happen with any new brand of technology and it just costs money.
When digital signals are sent through the channels they still receive resistance. It’s however on a lesser scale due to the encryption and so on. Using basic numbers such as 0 and 1 in a methodological approach can assist in fixing these errors. There will always be some sort of deviation from the original signal, however today things need to work to
their optimum performance levels. Analogue in its day was just that but is now far too outdated. With such extreme advances in technology, digital is the way forward.
Role of the Modem
The modem is vital for making communications happen in computing. It’s the central figure of the way communications from computer to computer occur. As described, computers are forms of digital applications. They are in turn only capable of producing a digital output. As the globe has only been using analogue signals to communicate for the last 10 – 20 years, this rather limits opportunity in sending digital data from one computer to another. Phone lines are all forms of analogue signaling and this is perfect for telephone calls, however this generation need more. For information to be sent over the internet it MUST be passed through a phone line. The phone line is the channel where the signaling error takes place. As previously mentioned phone lines only send analogue signals, so how do they pass through as digital? Well the answer is they are modulated. This is part of the role of the modem.
Different Types of Modulation
There are three kinds of modulation that take place on a daily basis. They are Amplitude Modulation, Frequency Modulation and Phase Modulation. They are all ways of modulating a digital signal from the computer to be able to pass freely down the phone line to its desired destination. As analogue wave signals can only pass through a phone line this operation becomes an imperative task. The difference between Amplitude and Frequency is given in the name. Amplitude is varied by the way it changes its height and strength of the wave. Frequency is varied by its timing; this is what makes then the two different. The two are well associated with radio and are the different forms in which the signals are sent. Phase modulation is another variant form however this time is changed by varying the angle of the wave to allow a different kind of signal.
Figure 1 is a basic example of a digital signal that would have left a computer on its way to the modem to be sent to its destination. As previously said, a digital signal has values of 0, 1 making the error correction possibility higher due to logical methods of repair. To be sent this can be modulated into the three different forms. It’s done by changing the values of 0 and 1 to wave forms and they come in different variations.
For amplitude Modulation 0 =
For amplitude Modulation 1 =
This process is continuous in the fact that for different forms of modulation the values are changed into analogue form. overleaf will be examples of Frequency Modulation and Phase Modulation using the digital signal from figure 1 as a constant reference.
For frequency modulation 0 =
For Frequency Modulation 1 =
For Phase Modulation 0 =
For Phase Modulation 1 =
Once the signals have been modulated into their variant forms they are then able to be sent through a channel. What form the digital signal is modulated into depends on the nature of what it shall be used for. For Radio the likely hood will be that it will be in either a Frequency or Amplitude modulated signal. This is due to the channel it is being sent through. The channel it’s being sent through constrains the signal to be sent. Amplitude is suitable for radio as it can increase the amps of wave strength to suit whilst the frequency remains a constant. Frequency modulation is commonly preferred today due to its vast array of differences although it does use a much higher bandwidth than its counterpart. It’s an adaptable radio wave and comes in many forms. It has a narrow band feature which can be used in day to day radio for speech and music. Narrow band ensures that a low bandwidth is to be used. Further, frequency modulated waves are used to record on basic VHS recording systems. VHS has a large range of frequency components which range from a few mega hertz to several.
