Analog to Digital (A/D) Conversion
As with frequency measurements, the
sample rate is measured in terms of
cycles, or hertz
 A rate of one sample per second would be
designated 1 Hz. A rate of 1000 samples
per second would be 1 kilohertz, or 1 kHz.
 Typically, audio signals for CDs and other
digital music are sampled at 44.1 kHz or 48
kHz.
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Analog to Digital (A/D) Conversion
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When reconstructing an encoded analog
signal, the higher the sampling rate and
the greater the number of bits in each
sample, the more accurate the analog
reconstruction can be.
Pulse Code Modulation (PCM)
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Pulse code modulation is the most
common method of digitizing data for
transmission.
Data transmission using PCM is serial,
which means that the binary words are
sent one after another in the order they
were generated.
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The circuitry that converts the data also sends
a timing, or clock, signal so the receiver can
synchronize itself with the data that is being
transmitted and reconstruct it accurately.
In order for pulse code modulation to be
effective, an analog signal must be sampled
at a rate that is at least twice the highest
expected frequency, this is called Nyquist
Therom.
Nyquist Therom
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For example, in a telephone conversation,
the highest frequency encountered is
about 4 kHz.
That means sampling must take place at
the Nyquist Minimum of 8 kHz to maintain
a basic signal quality
Multiplexing
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Most fiber optic data transmission systems
can send data at speeds that far exceed
the requirements of single stream of
information.
Multiplexing can be used to carry several
information channels, such as telephone
conversations, nearly simultaneously.
Multiplexing is the process of transmitting
many channels of information over one
link or circuit.
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A multiplexer first divides each channel into
several parts. In a process known as
interleaving, the multiplexer sends the first part
of each channel, then the second part of each
channel, continuing the process until all of the
transmissions are completed.
 At
the receiving end, a demultiplexer
separates
the transmissions into their
individual channels and reassembles them in
their proper order.
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Decibels (dB)
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When the light travels from its source
through a medium, it loses energy.
The decibel was originally used to
measure the strength of sounds as
perceived by the human ear.
To calculate the decibel value of a gain or
loss in signal power, use the following
equation:
dB = 10Log (P  P )
10
out
in
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To calculate the gain or loss If the
decible value is known:
(P  P )= antilog(dB  10)
out
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in
Calculate the power loss in decibels of a signal that starts at 3
milliwatts and arrives at 1.8 milliwatts.
1. Use the dB equation dB = 10Log10(Pout Pin).
2. Plug in the Pin and Pout values: dB = 10Log10(0.0018 0.003) =
10Log10(0.6).
3. 10Log10(0.6) = 10 * –0.2218 = –2.218.
4. The power loss in dB is –2.218.
Thank you