During the constant amplitude part of the modulating frequency.
What part of the modulating signal controls the amount of phase shift in PM?
What part of the modulating signal controls the rate of phase shift?
What is the advantage for using QPSK over BPSK?
Faster data rates, doubling the data carrying capability over BPSK.
How can higher levels of PSK be achieved?
Smaller phase shifts to allow for more phase shifts and increased capacity as each shift represents more bits in combination.
Define the term digitization.
The process of converting an analog signal into a digital signal.
Name the four steps of PCM.
State the main purpose of the band-limiting filter.
To ensure the input to the sampler never exceeds the max frequency.
Converting a continuous time signal into a discrete time signal.
What part of the pulse train is varied using PAM,PWM, and PPM?
What s the Nyquist sampling rate?
Taking samples at twice the highest frequency in the bandlimited signal.
Which step of PCM assigns discrete amplitude values to the sampled amplitude values?
Name two methods of quantization.
Which method of quantization assigns amplitude values based on an equal amplitude range?
With ATM, what is the length of each transmission unit?
What part of an ATM transmission tells the receiving device that a character is coming and that the character has sent?
Start and stop bits.
How does the receiving device determine whether it has received a correct character?
By summing the 1 bits. If the character arrives with an even number of 1 bits, the device assumes that it has received a correct character.
What is an advantage of synchronous transmission over asynchronous transmission?
Reduce the overhead cost of data transmission.
Not prone to distortion.
How does synchronous transmission differ from asynchronous transmission?
Synchronous blocks many characters together for transmission.
What does VRC check each incoming character for?
Odd or even parity.
In LRC, what transmission character does the receiver use to determine if a transmission was error-free?
BCC Block Character Count
When using the checksum method of error detection, what binary number is used to divide the sum of all the characters in order to derive the checksum?
How does the CRC method of error detection determine the dividend when computing the BCC?
The CRC treats the binary ones and zeros in the frame address, control, and information fields as a single long binary number.
How effective is CRC at detecting errors in most applications?
How does ARQ work?
The receiver automatically sends a re-transmittal request to the sender if it finds an error in a receiving frame.
Using forward error control, at which end of the transmission link are errors corrected?
Using forward error control, what is the transmitter's function in error detection?
To send multiple copies of the same message to the distant end.
Using forward error control, what is the receiver's function in error detection?
To compare all the copies and then reconstruct a message by using the good portions of the message copies received.
What are the three basic components that make up a fiber optics link?
Name the three components that make up the optical transmitter?
What are the three main types of light sources for optic waveguides?
Semiconductor laser diodes LD
Non-semiconductor laser diodes LD
Give the three main requirements of a light source.
Operating speed or rise time must be fast enough to meet the application's bandwidth requirements.
Must provide enough optical power through the fiber to operate the detector.
It must produce a wavelength that takes advantage of the fiber's long-loss propagation characteristics.
What are the advantages of LEDs over lasers?
Small size, ruggedness, capability of single and direct modulation, reduced expense, and spectral match with both fiber waveguides and silicone photodetectors.
What are the two basic designs of LED?
How are lasers different from LEDs?
LED's light output is incoherent
Laser's light output is coherent
How are lasers' output power measured?
What are lasers sensitive to?
What factors limit a detector's performance?
Dispersion or attenuation.
What two factors control the light signal that's received by the detector?
Noise floor (Noise equivalent power)
Signal-to-noise ratio SNR
What terms refer to the relationship between the signal and noise?
Signal-to-noise ratio SNR
Bit error rate BER
Upon what does a detector's responsivity depend?
Wavelength of light.
What are the two main types of photodetectors?
Positive intrinsic negative (PIN) diode and the avalanche photodiode (APD)
For what type of application are APDs ideally suited?
High-speed, long-distance applications.
What are the purposes of repeaters in a fiber optics communications link?
To extend the distance and to preserve signal integrity.
How do regenerators work?
Regenerators receive incoming low-level, dispersed (distorted) digital pulses. After conversion to the electrical domain, the pulses are regenerated (the leading and falling edges are sharpened and the pulses are amplified). Finally the regenerated pulses are retransmitted optically.
Which repeater device does not require converting to and from the electrical domain for signal amplification?
Describe the differences between a fiber optic patch cord, pigtail and breakout cable.
Fiber optic patch cord- short section of single fiber cable with a connector on each end. Each end is connected to a patch panel to connect circuits together.
Pigtails- similar to patch cords but they only have a connector on one end- the other end is spliced to the fiber optic cable.
Breakout cables- similar to pigtails but they are spliced to multifiber cables.
_____ connectors have conical shape.
_____ connectors use push-pull arrangement for mating.
SC Subscriber Connector
_____ connectors are used in high-vibration environments.
FC Field Connector
_____ connectors are the most widely used fiber optic connectors for local area networks and premise wiring.
ST Straight Tip
The _____ connector uses threaded coupling nut without a keying device.
The _____ connectors were the first connectors used on single-mode fiber optic cable.
What are "tunable" fiber optic connectors?
It means the keying slot in the connector can be rotated to find the optimal alignment.
Why are SC fiber optic connectors better for use in high-density applications than other types of connectors?
The other types of connectors require room to twist them for alignment. SC connectors use a push-pull arrangement and do not need this extra room.
What is one reason for modulation that involves modulating low frequency signals for transmission over long distances? a. Spectrum conservation b. Channel allocation c. Ease of radiation d. Companding
c. Ease of radiation
What are the three general categories used to produce modulation in RF transmission today?
When the modulating signal and carrier signal are combined within a modulator, the output signal contains
If a carrier frequency of 1MHz and a modulating tone of 10kHz goes to the modulator, the output signal will include
1.01MHz, 1MHz, and 0.99MHz
The bandwidth of an amplitude modulated signal is
two times the modulating signal.
If an oscillloscope displays a modulation envelope having an Emax of 200 volts and an Emin of 20 volts, what is the modulation percentage?
Which statement concerning bandwidth is true? a. Overmodulating increases bandwidth because the distortion produces harmonics. b.Undermodulating increases bandwidth because the distortion produces harmonics. c. Overmodulating increases bandwidth because the output's increased amplitude. d. Undermodulating increases bandwidth because the output's decreased amplitude.
a. Overmodulating increases bandwidth because the distortion produces harmonics.
The output of the oscillator in a FM modulator increases in frequency with each
positive half cycle of the carrier.
In FM, a significant sideband contains at least what percentage of the total transmitted power?
What is the formula to find the modulating index?
A 5 kHz modulating signal has enough peak voltage to cause a deviation of 15 kHz. What is the modulation index?
What is it called when a narrow frequency band between adjacent stations prevent frequency modulated sidebands from overlapping?
In PM, what part of the carrier signal is varied?
In phase modulation, the carrier's a. phase is shifted at the rate of the modulating signal. b. phase shifted with the phase of the modulating signal. c. amplitude is shifted at the rate of the modulating signal. d. amplitude is shifted with the phase of the modulating signal.
a. phase is shifted at the rate of the modulating signal.
What is the first step in the pulse code modulation process?
The analog signal is band limited.
In asynchronous transmissions, what bit is used by the receiving device to verify that the transmission was received correctly?
If an error should occur, what transmission is lost in a synchronous transmission? a. One character b. Block of data c. A parity bit d. A stop bit
b. Block of data
When using vertical redundancy check, what significance does the amount of ones have in a data bit pattern?
What error detection method is used for checking a data block greater than 512 and is about 99% effective in most applications?
Cyclic Redundancy Check CRC
Light sources that are applicable to fiber optic waveguide are light-emitting diodes and
Semiconductor laser diodes
What type of light is emitted from a laser?
What photo detector converts one photon to one electron?
Positive intrinsic negative diode
Which repeater amplifies optical signal without converting to and from the electrical domain?
A short section of single fiber cable that has a connector at each end is called a
Which fiber-optic connector uses quick-release, keyed bayonet couplings that are preferred in situations where severe vibrations are not expected?