Analog Communication Systems

Topics: Modulation, Frequency modulation, Amplitude modulation Pages: 10 (2753 words) Published: May 17, 2013
Analog Signal Transmission

Rafia Awan
Reg. No: FA09 BET 076
Student, Department of Electrical Engineering
COMSATS Institute of Information Technology
Islamabad, Pakistan

Abstract— the document presents the basic transmission system of analog signal over a distance. Different techniques most advantageous to different transmission systems are discussed. Elements used, like modulators, filters, mixers, power amplifiers, and channel media while transmission are also analyzed. The report presents different methods of generation of AM, carrier generating oscillators, frequency mixers, FM generation via VCOs and NBFM generation.

Keywords— Analog modulation; Bandwidth; Chopper circuit; Crystal oscillator; Impedance matching; RF power amplifiers and filters; Telephone microphones Introduction
nalog transmission is still put into practice but holds its own drawbacks. Analog information signals in their raw form cannot be transmitted, they need to be processed and prepared before that. The reasons why such a need arises are briefly discussed below and throughout the document. A. Bounded Canvas

This step can be excluded if digital transmission is not a preference; analog signals can be transmitted without undergoing A/D conversion. But because the human senses do not necessitate the precision to be infinite to be able to comprehend something (a signal), sampling and quantization processes barely effect the information but significantly reduce the cost. B. Antenna Practicability

For antenna practicability the need for the signals to have a much higher frequency than they customarily do rises, which is accomplished through modulation. However it raises the call for of a higher bandwidth than the information signal alone acquires. Bandwidth then again is too expensive an entity to squander. A fine modulation technique takes that into account. C. Bandwidth Efficiency

SSB filters filter one of the sidebands and as a consequence save power and bandwidth at the receiver end. RF power amplifiers further increase the power of the modulated signal to a suitable level for transmission. For different channels to share a bandwidth FDM is used. But Quadrature Amplitude Modulation technique sends two signals on the same bandwidth which in the process saves bandwidth too. Signals are after being processed are fed to the transmission channel/media, be it antenna or co-axial cables. Channel is the major culprit for the introduction of noise and distortion in the intelligence signal which the receiver end must be capable of handling while demodulation. In the end, the document describes the pros and cons of the different configurations. Comparison Between Analog and Digital Transmission

An analog signal offers an unnecessarily high quality signal but digital systems that take the sampled and quantized versions of the analog signals and do not even contain the precise information, can amazingly transmit higher quality signals than analog systems. Analog modulated signals while transmission loose amplitude and undergo distortion and noise introduction which drastically affects the quality of the received signals. Digital signals too need to be transmitted through the same analog channels and similar channel losses come into the picture, but digital systems tend to be more noise resistant; they convert the signal into bits before transmission. So at the receiver end the quality of the received signal doesn’t matter given that the recognition of the zeros and the ones is still possible. This promises zero noise in the signal and makes digital transmission superior. The first generation technology analog AMPS was long ago replaced by the later ones, but telephony predominantly still rehearses analog though there are digital telephone systems which tend to be cheaper for they offer a high quality at a lesser bandwidth but this feature makes them prone to overcrowding. Moreover, analog...
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