Ntc362: Analog and Digital Comparison Paper

Analog and Digital Comparison Paper

Amanda Dyer, Derick Campos, Jesse Ford, Mehran Gerami, Nicolas Monteiro, Wendell Taylor

NTC/362

October 15, 2015

Richard Swafford, Jr.

Analog and Digital Technology: A Comparison

Analog and digital are two different types of signals used to transmit audio or visual information from one place to another.  Analog signals are continuous, meaning that there are no breaks or interruptions and digital signals are not continuous, they use specific values to represent information (Strickland, 2008).  Analog transmissions are sent via electronic pulses of varying amplitude, while digital transmissions are converted into binary format to represent two individual amplitudes.  Analog is cheap and has been used quite some time now, but the biggest issue with analog signals is the limitation of data that can be transmitted.  Nowadays almost all equipment being produced is digital based.

Analog to digital conversions or A/D conversions is the process of changing a continuous variable signal to a multi-level signal without altering the vital contents or the information or data.  A prime example of a telecommunication that uses this form of conversion is a telephone modem.  Voice communications vary in range and are not in binary form, so these analog signals must be translated into digital signals.  Digital to analog conversions or DAC is the conversion of binary code to analog signal.  In order words, signals having few defined levels or states are converted into signals having a theoretically infinite number of states (Rouse, 2005).  Going from digital to analog can sometimes be tricky and even cause the quality of the signal to be compromised.  An example of digital to analog conversion would be the use of Internet via a modem; the modem converts computer signals (digital) using standard phone lines.

Amplitude Modulation & Frequency Modulation

Analog and Digital signals can now be understood as types of signals, or wave forms that are used to transmit the audio or visual information from one place to another.  The next step is understanding how the signals (wave forms) can vary and the advantages and disadvantages of those wave forms modulation types, in either a transmitted or received signal.  

Two types of modulations are Amplitude Modulation (AM) and Frequency Modulation (FM).  The textbook defines ‘amplitude’ as a measure of the height of the wave (signal), which indicates the strength, or power, of the signal, and ‘frequency’ as the number of oscillations per second of an electromagnetic wave (Goleniewski, 2007).  AM signals are known to modulate in amplitude by the signal that is to be transmitted.  FM signals are known to modulate in frequency by the signal that is to be transmitted.  Although it is cheaper, AM has poorer sound quality and in FM, it is much more reliable security wise because the signal can be encrypted (Poole, 2015).

These are just a few of the advantages and disadvantages, and depending on the transmission modulations and signals being used, meeting the endpoint can be determined from these factors, as far as clarity of signal goes for audio and video.  

Phase Modulation (PM)

Phase Modulation (PM) is the modulation technique in which carrier phase varies based on analog baseband information signal to be transmitted using wireless device. Phase modulation is referred as indirect frequency modulation due to the fact that phase modulation produces frequency modulation. The advantages and disadvantages of phase modulator differ from other modulators. For example, one advantage is the phase modulation & demodulation can be easily compared to frequency modulation. In other words, if one understands frequency modulation they should have no problem understanding phase modulation. Another advantage of phase modulations is that it is used in determining velocity of moving targets by extracting Doppler information. Doppler information refers to the Doppler Effect which is the change in frequency of a wave. Doppler information needs a stable carrier, which is possible in phase modulation but not in frequency modulation.  On the other hand, here are some disadvantages of phase modulation. One disadvantage of phase modulation is that phase ambiguity comes into effect if you go pass its modulation index (180 degree). This means the frequency output signal becomes inverted in relation to the input. Another disadvantage is that you need frequency multiplier to increase phase modulation index.

Quadrature Amplitude Modulation (QAM)

Quadrature Amplitude Modulation, also known as QAM is a method of combining two amplitude-modulated (AM) signals into a single channel, thereby doubling the effective bandwidth. One of its advantages is its capability to increase the efficiency of transmission due to the use of both amplitude, and phase variations in radio communications. However, its disadvantages are that in order to move the signal to a different decision point, the lower levels of noise are needed. This noise may present a problem with QAM. QAM also contains an amplitude component and a linear amplifier is needed for transmission. This is also a disadvantage because the use of linear amplifiers consumes more power thus making it less desirable for mobile applications.

Modulation Techniques

The word modem is actually an acronym that stands for Modulation/Demodulation. A modem also allows for two computers to communicate I each other. The term modulation is defined as the alteration of a carrier signal based on whether it is transmitting a 1 or zero. Modulation is required in order for the transmission of digital information to take place. Modulation methods vary, for example, the type of wire needed, the immunity to noise and the overall complexity requirements may result in incompatibility issues (Feibel, 2000). 

56k Modem

56K modems modulate by utilizing ordinary telephone lines. In order for the modulation to complete successfully, the lines cannot be multiplexed. Multiplexed lines are commonly used in areas that are densely populated. If these lines were to be used, there would be too much noise on the line to successfully transmit the data and information through the line. It is also recommended that a user of the 56k modem reside within one to two miles of the phone company’s central office. Anyone who uses a 56k modem outside of this distances takes the risk of not having a clean line for the transmission of their data (Feibel, 2000).