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State the equation for the number of decibels.
Number of dB = 10 lg( P₁ \P₂)
What are 2 ways to improve the reproduction of input signal
1. Increase the number of bits . number for each sampling so that the step height is reduced. 2. Increase sampling frequency so that the depth isis reduced.
What are some advantages of digital to analogue?
The signal is able to be regenerated so there is minimal noise. Extra data can be added so the signal can be checked for errors.
What is the function of an analogue to digital converter?
The analogue signal is sampled at a number of regular time intervals and then each is converted to a binary number.
Which is a digital signal?
A digital signal is a signal which consists of a series of highs and lows with no intermediate values.
What is an analogue signal?
An analogue signal is a signal that has the same variation with time as the data does.
Which transmission media has the highest bandwidth?
Optical fibres.
What is the advantage of a small FM frequency deviation?
Less frequency deviation means more channels can fit into the same frequency spectrum.
Do FM or AM signals have higher noise immunity?
FM.
Define, using a formula, FM bandwidth.
FM bandwidth= 2 x (Δf + fM) fM is the peak frequency of the modulated signal.
What is frequency deviation, Δf ?
The maximum variation in frequency.
What is the effect of frequency modulation (FM) on the amplitude of the carrier wave?
None, the amplitude is constant but the frequency is varied depending on frequency variations of the audio signal.
What is the relationship between AM bandwidth and the highest frequency in the audio signal, fH?
In amplitude modulation (AM), the carrier waveform amplitude is altered depending on variations in the audio signal: AM bandwidth = 2fH
What process do high-frequency carrier radio waves undergo before transmission over long distances?
Modulation using audio signal information.
How do geostationary satellites and ground stations avoid de-sensing?
They transmit at different frequencies.
What are microwave links?
Line of sight transmission paths to receive and transmit information at microwave frequencies.
What are sky waves?
Radio waves reflected from the ionosphere by total internal reflection.
What are surface waves?
Radio waves that diffract over the curvature of the earth to cover large distances.
How do optical fibres transmit a signal?
By total internal reflection of light in a long, thin glass cable with a core and cladding.
What two forms can metal wire be found as in communication systems?
1. Coaxial cable. 2. Twisted pair cable.
What is meant by transmission path?
The physical medium over which the information is transmitted.
What are 4 reasons for modulation?
1. Less interference. 2. A shorter aerial can be used. 3. Less attenuation. 4. Less distortion.
What is modulation?
The process of impressing information onto a signal carrier.
What is a communication system made up of?
System blocks, each with an individual function in transferring a signal from source to receiver
What are 3 advantages of optical fibres compared to coaxial cables?
1. Larger bandwidth. 2. Lower attenuation of signal. 3. More secure.
What are Coaxial cables?(constructure, uses)
2 wire conductors, a signal transmits through a conductor which is surrounded by an insulator, an earthed wire braid protects from any interference.
What are wire pairs? One example of uses
Wire pairs are links between information transmitters and receivers. Nowadays they are used for low frequency short distance communications, e.g. doorbells.


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