Study Sheet Flashcards
What is sound?
Audible frequencies created by a source such as a person talking.
A periodic variation in air pressure.
travels in form of sound waves
types of sound waves
Pressure waves that vibrate molecules in a medium such as the air.
high frequency vs low frequency
loud vs soft (amplitude)
pleasant vs noise
frequency
number of cycles per second
Number of events happening over a defined time period.
wavelength
length of the waveform
The length of one complete waveform. The higher the frequency, the shorter the wavelength; and the lower the frequency, the longer the wavelength.
what is a decibel used for
unit used to measure signal strength
used on a logarithmic scale
convert decibels to milliwatts
10 milliwatts equals how many decibels
100 milliwatts equals how many decibels
10mw = 10dbm
100mw = 20 dbm
milli watts on the x axis and decibels on the y
to double a milliwat is how many decibels
3
human ear can hear from qhat decibel to what decibel
0-120
formula to convert power to decibels
Decibels (dB) = 10 log(P2/P1)
P1 is reference and P2 is output
frequency of human hearing
20 Hz
20,000Hz
20kHz
frequency of human speech
400 hz
4,000 hz
4khz
local loop
subscriber loop consisting of twisted pair connecting each phone to local exchange.
has both DC and AC power
ADSL
Asynchrnous Digital Subscriber Line
used for internet access on same wires
local exchange office does what
provides power to telephone circuits
dial tone
ring signal
other info and billing tracking
circuitry for routing
ringing voltage
90 VAC at 20 hz
where do telephones enter home business
demarcation point
subscriber interface
LEC
local exchange carrier
local companies that provide phone service
LATA
local area and transport network
geographic regions
POP
point of presence office for that compnay in a LATA
trunks for long distance carriers are called
IXC;s
inter exchange carrier
IXC
interexchange carrier
what is DTMF
Dual Tone Multi Frequencey
used for dialing and sending the number input as a frequency to the central office
Steps of Analog to Digital conversion
Sampling-8000 times
Quanitizing: compares to 255 level scale
Encoding: Translating PAM sample into PCM word converted into bipolar signal and multiplexed into DS-1
digital modulation techniques
ASK-amplitude FSK-frequencey PSK-phase shift QAM-quadrature amplitude PCM-pulse code modulation
