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3-The Decibel Notation

# 3-The Decibel Notation - main amplifier and the power...

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PRINCIPLES OF COMMUNICATIONS 3 - THE DECIBEL NOTATION AND ITS APPLICATION IN TRANSMISSION GAIN AND LOSS CALCULATION

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TRANSMISSION GAIN / LOSS AND DECIBELS Decibel measurement was based on a comparison of two power levels. Transmission systems utilize amplifiers, devices that provide an increase in power level (gain). Also, passive devices are present, such as attenuator networks (cables, connectors, etc.) and filters, devices that lower the power level (loss). It is therefore necessary to perform transmission power calculation on several points of a transmission system
POWER GAIN AND LOSS Two-port System used for defining gain/ loss

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DECIBEL MEASUREMENT Decibel is not an absolute unit, rather it compares one quantity with another. However to say that a signal level is a certain decibels above a reference level is proper. Decibel measurements are made using standard reference levels
PROBLEM SET 1. Show that the power level (dBm) = power level (dBW) + 30. (5pts) 2. Determine the output power of the preamplifier, the

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Unformatted text preview: main amplifier and the power amplifier if the signal from the tape head has a value of 3 μW. 3. A certain cable signal transmission is shown in Figure 1. The nominal level at the signal source output is 10dBm. The signal is amplified before transmission by the line amplifier whose gain is 13 dB. The first cable section (section A) has a loss of 26 dB, and a booster amplifier with a gain of 20 dBm is placed at the output of that section. The second section of cable (section B) has a loss of 29dB. The system is operated on a matched impedance basis with all effective sources and terminations having a resistive impedance of 600Ω, and the characteristic impedance of the cable is the same. (a) Determine the signal level both in dBm and volts at the output of the line and booster amplifier. (b) Determine the gain of the receiver amplifier such that its nominal output level is 6volts (V) across a 600-Ω termination. END...
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