LQ1 - Digital Communication - Electronic Comm. Fundamentals

Gain and Attenuation

Terms that describe the change in signal level of the output of the transmitter to the input of the receiver in a communication system.

Gain

Refers to amplification

A = O/I, O>I

Formula for gain

L = O/I, O < I

Formula for attenuation

Attenuation

Refers to loss

single, stage, multi, stage

Attenuation can be ___-___ or ___-____

Attenuation

Is an expected occurrence when a communication signal travels from one point to another

Gain

Is used to counteract the effect of attenuation to increase range or to mitigate the effect of noise

Decibel (dB)

a logarithmic way of expressing a ratio

1. audio, loudness

2. gain, attenuation

Decibel:

1. Was originally used to measure ___ ____

2. Conveniently expresses ___ and ___

20log(output/input)

gain formula

Modulation, carrier, modulating

The process of manipulating a signal using another signal to convey information about the 2nd signal. The 1st signal is referred to as the ___ signal, while the 2nd signal is referred to as ___ signal.

1. better transmission

2. multiplexing

Why modulate:

1. to take advantage of the carrier for ____ ____

2. to perform ___

Amplitude modulation

A type of modulation that encodes information into a carrier signal by manipulating its amplitude

sinusoidal, wave, V_c = A_c sin (2 pi f_c t)

In amplitude modulation, the carrier signal is a ___ ___. Its formula is ________

V_m = A_m sin(2 pi f_m t), where f_c » f_m

Formula for amplitude modulation modulating signal

C_m = (1 + m sin(2 pi f_m t)) A_c sin(2 pi f_c t))

Formula for the amplitude of the modulated signal

spectrum, modulating, frequency, carrier

Modulation shifts the ___ of the ___ signal to the ___ of the ___ signal

LSB

lower sideband of spectrum

USB/FSB

upper sideband of the spectrum

Frequency Modulation

A type of modulation where the carrier frequency is modulated

Phase modulation

A type of modulation where the carrier phase is modulated

Filters

Circuits capable of amplifying a range of frequencies while attenuating frequencies outside of the range

transfer, function, voltage, ratio, power, ratio

Filter response is characterize by its ___ ___

(Vo/Vi) vs freq - ____ ___

(Po/Pi) vs freq - ___ ___

Cut-off frequency

Delineates the pass band from the band stop regions

-3 dB

Typical ratio for cut-off frequency

Slope/roll-off

Indicates the sharpness of attenuation

dB/octave, dB/decade

Slope or roll off is often expressed in ___ or ____

1. wanted signals

2. attenuate

3. bandwidth

What are filters for?

1. To allow ___ ___

2. To ____ unwanted signals

3. To limit the ____ of signals

Transmission medium

Can be treated as a filter