Term
| What are the two primary purposes of modulating a signal? |
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Definition
1. Ease of radiation 2. Channel Allocation |
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Term
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Definition
Allows us to transmit low frequency signals at higher frequencies. |
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Term
| What must we do first to radiate a signal over long distances? |
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Definition
| First change them to an analog format by using a modulation technique |
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Term
| name the part of the AM carrier that varies according to the modulating signal. |
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Definition
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Term
| What frequencies are present at the output of an AM modulator |
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Definition
Carrier Frequency Carrier plus the Modulating frequency Carrier minus the modulating frequency |
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Term
| What would be the frequencies at the output of the modulator when you modulate a 500 kHz carrier with a 2 kHz tone? |
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Definition
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Term
| In conventional AM (DSBEC), what is the relation between the bandwidth required to transmit the signal and the bandwidth of the modulating signal? |
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Definition
| The bandwidth required is twice the modulating signal |
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Term
| What part of the bandwidth of a DSBEC signal carries the information signals? |
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Definition
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Term
| State the main disadvantage of DSBEC AM |
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Definition
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Term
| What determines the amount of deviation of a FM carrier? |
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Definition
| The amplitude of the modulating signal |
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Term
| how does the rate of deviation relate to the frequency of the modulating signal? |
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Definition
| They are directly proportional |
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Term
| Who determines the maximum amount of deviation in FM? |
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Definition
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Term
| How do you determine the modulation index in FM? |
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Definition
| By dividing the amount of frequency deviation by the frequency of the modulating signal. |
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Term
| What is a significant sideband? |
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Definition
| A sideband that contains at least 1 % of the total transmitted power. |
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Term
| WHere do FM sidebands get their power? |
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Definition
| From the unmodulated carrier |
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Term
| What is the relationship between modulation index and sideband power? |
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Definition
| higher modulation index means more power in the sidebands. |
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Term
In PM, what effect does the change in carrier frequency have? |
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Definition
NONE, the frequency change in PM is incidental |
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Term
| Describe the effect the positive and negative alterations of a modulating signal have onthe phase of the carrier in the PM. |
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Definition
| during the positive alternation of the modulating signal, the phase of the carrier lags behind the unmodulated carrier. During the negative alternation it leads the unmodulated carrier. |
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Term
| When is the carrier at its REST frequency in PM? |
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Definition
| During the constant amplitude of the modulating frequency |
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Term
| What part of the modulating signal controls the amount of phase shift in PM? |
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Definition
|
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Term
| What part of the modulating signal controls the rate of phase shift? |
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Definition
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Term
| How can you increase efficiency in digital modulation? |
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Definition
| By using multilevel encoding |
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Term
| Describe the QPSK process. |
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Definition
| The input NRZ signal is split into two directions ( I-rail and Q-rail), each at half the data rate. The Q-rail signal is phase shifted 90 degrees and both are modulated in bi-phase modulators. The signal are recombined to for the QPSK signal |
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Term
| What are the two reasons for using higher levels PSK? |
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Definition
| To increase capacity or decrease modulation rate |
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Term
| How many bits are grouped in 8 PSK? |
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Definition
|
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Term
| How many bits are grouped in 16 PSK? |
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Definition
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Term
| What is the main disadvantage of higher level PSK? |
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Definition
| You need a higher S/N ratio |
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Term
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Definition
| The process of converting analog signals to digital signals. |
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Term
Name the four steps of PCM ( Pulse Code Modulation) |
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Definition
Band limiting sampling quantizing encoding |
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Term
| State the main purpose of the band-limiting filter. |
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Definition
| It ensures the input to the sampler never exceeds a maximum frequency |
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Term
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Definition
| Converting a continuous time signal into a discrete time signal. |
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Term
| What part of the pulse train is varied using PAM, PWM, and PPM? |
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Definition
PAM=Amplitude PWM= Width or duration PPM=Position |
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Term
| What is the Nyquist sampling rate? |
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Definition
Sampling the input at twice its highest frequency |
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Term
| Which step of PCM assigns discrete amplitude values to the sampled amplitude values? |
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Definition
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Term
| Name 2 methods of quantization. |
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Definition
Uniform quantizing Non-Uniform Quantizing |
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Term
| Which method assigns amplitude values based on an equal amplitude range? |
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Definition
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Term
| WIth ATM, what is the length of each transmission unit? |
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Definition
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Term
| What part of an ATM transmission tells the receiving device that a character is coming and that the character has been sent? |
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Definition
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Term
How does the receiving device determine whether it has received a correct character? |
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Definition
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Term
| What is an advantage of synchronous transmission over asynchronous transmission? |
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Definition
| To reduce the overall cost of data transmission. |
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Term
| How does synchronous transmission differ from asynchronous transmission? |
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Definition
| Synchronous transmission blocks many characters together for transmission. |
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Term
| What does VRC check each incoming character for? |
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Definition
|
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Term
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Definition
| There is an even number of 1's in the bit pattern for each character |
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Term
| What is the difference between VRC and LRC? |
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Definition
| VRC checks each character for odd parity ; LRC check an entire horizontal line within a block for odd or even parity |
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Term
| What transmitted character does the receiver use to determine if a transmission was error free? |
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Definition
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Term
| When using the checksum method of error detection, what binary number is used to divide the sum of all characters in order to derive the checksum? |
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Definition
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Term
| How does CRC method of error detection determine the dividend when computing the BCC? |
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Definition
| CRC treats the binary ones and zeros in the frame address, control, and information fields as one long binary number. |
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Term
| How effective is CRC at detecting errors in most applications? |
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Definition
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Term
|
Definition
| The receiver automatically sends a retransmittal request to the sender if it finds an error in a received frame. |
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Term
| What is the most common method of error correction? |
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Definition
| ARQ ( Automatic retransmit on Request) |
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Term
| On what type of circuits is forward error control most useful? |
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Definition
| On circuits with extremely high error rates or on 1-way broadcast circuits. |
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Term
| Using forward error control, at which end of the transmission link are errors corrected? |
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Definition
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Term
| Using forward error control, what is the transmitter's function in error correction? |
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Definition
| To transmit multiple copies of the same message to the distant end. |
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Term
| Using forward error control, what is the receiver's function in error correction? |
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Definition
| To compare all copies of transmitted message, then reconstruct the message using the good portions of the message copies received. |
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Term
| How do we define fiber optics (FO)? |
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Definition
| A technology in which light is transmitted along the inside of a thin flexible glass or plastic fiber.l |
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Term
| What is the most common use of Fiber Optics? |
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Definition
| Transmission link connecting two electronic devices or circuits |
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Term
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Definition
| The information carrier capacity of a carrier wave. |
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Term
Compare attenuation in Fiber optics to attenuation in metallic cables. |
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Definition
| Optical fibers have less attentuation (power loss) than metallic cables. |
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Term
| how are fiber optic cables affected by electromagnetic interference? |
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Definition
| Fiber optics are immune to this kind of interference |
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Term
| Why are communications over fiber optic cables highly secure? |
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Definition
| It is virtually impossible to tap a fiber optic cable unnoticed because the light carrying part of the core is so affected by the tap that it is easily detected. Since fiber does not radiate energy, other eavesdropping techniques are useless |
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Term
| Why do we use the metric system to measure fiber optics? |
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Definition
because fiber optic dimensions, weights and frequencies are generally very small or very large |
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Term
|
Definition
| One Thousandth of a meter |
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Term
|
Definition
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Term
|
Definition
|
|
Term
|
Definition
|
|
Term
| Name two safety precautions to observe when working with fiber optics. |
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Definition
DO NOT look into a laser beam. Always wear goggles to protect against flying fragments of silica. |
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Term
| What are the components of a typical fiber optic cable? |
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Definition
| Core, Cladding, and protective coating |
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Term
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Definition
| the optical transmision path that carries the lightwaves to the receiving end. It may be glass or plastic. |
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Term
| The fiber cladding surrounds the core. What is its purpose and what material is it made of? |
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Definition
| The cladding surrounds the core and provides the reflective surface that allowes light to propagate along the core to the distant end. It is also a solid section of transparent glass or plastic, but with much lower density than the core. |
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Term
| Name the three MAJOR types of buffering designs. |
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Definition
1. Tight buffer tube 2. Loose Tube 3. Ribbon |
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Term
| How is a loose tube buffer formed? |
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Definition
| Optical Fibers are usually coated with a thin layer of acrelate and then several fibers are placed in a hard plastic tube with an inside diameter several times larger than the diameter of the fiber. |
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Term
| What characteristic of the carrier wave does the energy possessed by the photon determine? |
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Definition
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|
Term
| Photon particles are a part of what spectrum? |
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Definition
|
|
Term
| What is the frequency range of infrared light? |
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Definition
|
|
Term
| Describe refractive index. |
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Definition
| It's the ratio of the speed of light in a vacuum to its speed in a given medium. |
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Term
| Light bends as it passes through materials of different density. What do we call this phenomenom? |
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Definition
|
|
Term
|
Definition
| it is bouncing back of light from an object |
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Term
| What are four basic facts that we must consider in understanding lightwave propagation? |
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Definition
1. The normal 2. The angle of incidence 3.The angle of refraction 4. The angle of reflection |
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Term
| What happens to light when it passes from a higher index material to a lower one? |
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Definition
| It's bent away from the normal. |
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Term
| Describe the critical angle. |
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Definition
| The angle of incidence that causes the angle of refraction to equal 90 degrees |
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Term
| What does Snell's law State? |
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Definition
| If a ray of light enters a junction of two media of different refractive indices beyond the critical angle, the light is totally internally reflected. |
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Term
| Describe numerical aperature |
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Definition
| It's a fiber's inherent light-gathering capability |
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Term
How is light affected in a cable that has a large numerical aperature? |
|
Definition
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|
Term
| How does a fiber reach equilibrium-mode distribution? |
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Definition
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|
Term
| How do we express the amount of power in a fiber optic link? |
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Definition
| In microwatts or milliwatts |
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Term
| To what can we attribute fiber-to-fiber connection power losses? |
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Definition
| Acceptance cone/ejection cone mismatches, fiber core diameter mismatches, connector insertion loss, and intrinsic fiber loss. |
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Term
| What unit of measurement do we use to express fiber optic attenuation? |
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Definition
| Decibals per kilometer (dB/km) |
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Term
| What are the two MAIN causes of attenuation in optical fibers? |
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Definition
1. Absorption 2. Rayleigh Scattering |
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Term
| What is spectral attenuation? |
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Definition
| It is related to light wavelengths and requires careful balancing of light sources and fibers. |
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|
Term
| How can we reduce Fresnel losses in a fiber? |
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Definition
| By using index matching fluids |
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|
Term
| What does nuclear radiation cause in fiber optic cables? |
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Definition
| Increased attenuation caused by absorption and scattering. |
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Term
| What happens when a fiber's bending radius is exceeded? |
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Definition
| It experiences macrobends or microbends |
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Term
| What is dispersion in a fiber optic cable? |
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Definition
| The spreading out of the light in the fiber |
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Term
| How does dispersion affect the bandwidth? |
|
Definition
|
|
Term
| What causes each of the two main types of dispersion? |
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Definition
1. Modal dispersion is caused by different paths of light in various modes 2. material dispersion is caused from different velocities of different wavelengths |
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Term
| How do we measure dispersion? |
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Definition
| In nanoseconds per kilometer (ns/Km) |
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|
Term
| Optical fibers are normally composed of what materials? |
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Definition
| Entirely of glass or silica, plastic-clad silica, or all plastic |
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Term
| How are optical fibers generally classified? |
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Definition
| By the number of modes and the core's refractive index profile. |
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|
Term
|
Definition
| A mathematical and physical concept describing the propagation of electromagnetic waves, but for our purpose its simply a path that light can take in traveling down a fiber. |
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|
Term
| The refractive index is a relationship between what elements of a fiber? |
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Definition
| The Core's refractive index and the cladding's refractive index |
|
|
Term
|
Definition
| This fiber has a core diameter of 30 to over 800um with a constant index of refraction, and with a step change in index at the cladding boundary. Allows many modes of light to travel. |
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Term
|
Definition
| Small Core diameter of 2 to 8 um helps eliminate dispersion. Propagates one mode efficiently. |
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Term
|
Definition
| Has a core diameter of 50-125um. The core has numerous concentric layers of glass that decrease in refractive index as they go away from the center. Light rays are refracted continously so that all modes tend to arrive at any point at the same time, reducing dispersion. |
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Term
| Which fiber classification has the highest dispersion factor? |
|
Definition
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|
Term
| Which fiber type is every efficient for long distance and very high speed applications, but is hard to work with? |
|
Definition
|
|
Term
| explain the purpose of the meter's range switch |
|
Definition
| To obtain any of the meter's range or functions |
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|
Term
| Where do you set the function switch for measuring resistance? |
|
Definition
|
|
Term
| how do you calibrate the meter pointer for zero ohms when you measure resistance? |
|
Definition
| Short the test leads together and adjust the zero ohms control to move the pointer to zero ohms |
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|
Term
| Which control compensates for the meter's internal batteries? |
|
Definition
|
|
Term
| Which circuit jacks get the most usage? |
|
Definition
| The common (-) and (+) jacks |
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|
Term
| WHen might you have to use the reset button? |
|
Definition
| When an overload (voltage or current) triggers the protection circuit, the reset button "clicks" or "pops up". Pressing down and releasing the reset button should return the meter to normal operation. |
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|
Term
| WHen preparing to measure resistance, what is the first thing you must do before you make a measurement? |
|
Definition
| be sure that no power is applied to the circuit and that all capacitors are discharged. |
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|
Term
| How often do you "zero" an analog multimeter during resistance measurements? |
|
Definition
| Each time you select a new range |
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|
Term
| How can you electrically isolate a resistor from its circuit when measuring resistance? |
|
Definition
| By disconnecting one of the resistor's soldered connections |
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|
Term
| On what part of the meter's scale can you best read resistance measurements? |
|
Definition
|
|
Term
| What is the difference between measuring DC voltage and AC voltage with regard to the test leads? |
|
Definition
| The polarity of the leads are not important when measuring in AC. |
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|
Term
| How do you place the test leads in a circuit when you measure voltage? |
|
Definition
| Place the test leads parallel with the load to measure voltage |
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|
Term
| How do you place the test leads in a circuit to measure current? |
|
Definition
| Place the test leads in series to measure current |
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