In electronics media, a signal is an electric current or electromagnetic field used to convey data from one place to another. The simplest form of signal is a direct current (DC) that is switched on and off, this is the principle by which the early telegraph worked. More complex signals consist of an alternating-current (AC) or electromagnetic carrier that contains one or more data streams.

Mainly two types of data signals are used while transferring information through electronic media. They are:

Analog signals are signals with continuous values. Analog signals are used in many systems, although the use of analog signals has declined with the advent of cheap digital signals. The primary advantage of an analog signal is that it’s much cheaper than a digital signal.

Digital signals that represented by binary numbers, 1 or 0. Ther 1 and 0 values can correspond to different discrete voltage values, and any signal that doesn’t quite fit into the scheme just gets rounded off. Unlike analog signals, digital signals are not constant. Instead, they constitute a series of pulses, each with exactly the same amplitude and lasting the same length of time. They don’t rise and fall the way analog signals do, and the pulses are cleanser. The digital signals can travel through digital lines much more quickly because they consist of binary code. This allows more data to be transferred, which results in s sharper, clearer signal.

The main difference between analog and digital technologies is that in analog technology, information is translated into electric pulses of varying amplitude. In digital technology, the translation of information is into binary format (0 or 1) where each bit is represented by two distinct amplitudes.

Modulation is the technique of adding the information to a carrier wave ready for transmission which allows a large number of communication channels to use the same transmission route. Therefore Modulation is the technique of converting a digital signal to its analog form, and demodulation is the reverse process of converting an analog signal to its digital form.

Following are the common three forms of Modulation techniques:

AM represents two binary values (0 and 1) of digital data by two different amplitudes of the carrier signal, keeping frequency and phase constant. Voice-grade lines use amplitude modulation up to 1200 bps.

FM represents two binary digital data by two different frequencies, keeping amplitude and phase constant. It is also known as Frequency Shift Keying (FSK), this method is less susceptible to error than amplitude modulation.

PM represents two binary values of digital data by a shift in phase of the carrier signal. That is a sine wave with phase =00 represents a digital 1, and a sine wave phase =1800 represents a digital 0. This technique is more noise resistant and efficient than both AM and FM techniques.

Modem stands for modulator and demodulator. It is an electronic device, which allows the computer to send and receive data through telephone lines. It is a combined device for modulation and demodulation (modulator + demodulator = modem). It modulates the digital signal (0 and 1) into an analog signal similarly, it demodulates the analog signal back into a digital signal. Modems send data by converting it into analog signals and receive it by converting analog signals back into digital form.

Modems are of two types, internal modems, and external modems. The modem fixed inside the casing is called an internal modem and the modem placed outside the casing is called an external modem. The internal modem usually uses a PCI (Peripheral Component Interconnect) Express slot on the motherboard. High-speed modems are typically external boxes, but we can find them in the internal variety for desktop computers. A laptop has external slots that can contain wired or wireless modems. A wireless modem may use Wi-Fi or a cell phone network.

Bandwidth is the amount of data that can be transmitted through a communication channel during a specified period of time. It is the data handling capacity of a communication system. The bandwidth of the digital signal is measured in bits per second (bps) whereas the bandwidth of the analog signal is measured in cycle per second (cycle/ sec) or Hertz. The bandwidth of the modem is measured in bits per second (bps). High bandwidth provides less data traffic whereas low bandwidth provides high data traffic.

The term bits per second (bps) are usually used to refer to the speed of different types of Internet services. Faster services are said to have higher bandwidth than slower ones. Dial-up Internet service is a low-bandwidth connection. Broadband services such as DSL, cable, and satellite Internet are typically high-bandwidth services. Some DSL services are as slow as 128 kilobits per second (Kbps). However, many services providers are offering high-bandwidth DSL service for 768 Kbps and over. Cable Internet service typically starts at 1 megabit per second (Mbps) and can theoretically go as high as 30 Mbps. Satellite speeds run between 1 Mbps and 3 Mbps.