Term
| What are the two primary purposes for modulating a signal? |
|
Definition
| Ease of radiation and channel allocation. |
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Term
| What must we do first to radiate a signal over long distances? |
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Definition
| The signal must first be converted to analog format. |
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Term
| Name the part of the AM signal that does not fluctuate in amplitude by the modulating signal. |
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Definition
|
|
Term
| What frequencies does the amplitude modulated waveform contain? |
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Definition
Carrier frequency, carrier plus the modulating frequency (USB), and carrier minus the modulating
frequency (LSB). |
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Term
| What part of the modulated carrier wave contains the information carrying component? |
|
Definition
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Term
In AM, what is the relation between the bandwidth required to transmit the signal and the
frequency of the modulating signal? |
|
Definition
| The bandwidth required is two times the modulating signal frequency. |
|
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Term
| The amount of effect or change that the intelligence has on the carrier. |
|
Definition
|
|
Term
| Find the % mod if a 4 Vpk-pk RF signal is modulated by a 2.5 Vpk-pk audio signal. |
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Definition
| The percent of modulation is 62.5 percent—found by dividing 2.5 by 4 and multiplying the result by 100. |
|
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Term
Emax of 50 mVrms and an Emin of 5 mVrms, what is its %
mod? |
|
Definition
|
|
Term
| What are two results of overmodulation? |
|
Definition
| Severe distortion and increases bandwidth of an AM signal. |
|
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Term
| What determines the amount of deviation of an FM carrier? |
|
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? |
|
Definition
| They are directly proportional. |
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|
Term
To prevent interferences with other FM stations, who establishes limits on the maximum amount
of deviation in FM? |
|
Definition
The FCC establishes the maximum
amount of deviation. |
|
|
Term
| What is a significant sideband? |
|
Definition
A sideband that contains at least 1%
of the total transmitted power. |
|
|
Term
| How do you determine the modulation index in FM? |
|
Definition
| Divide the amount of frequency deviation by the frequency of the modulating signal. |
|
|
Term
| Where do FM sidebands get their power? |
|
Definition
|
|
Term
| What is the relationship between modulation index and sideband power? |
|
Definition
A higher modulation index means more power in the sidebands. It is even possible to have all the power in
the sidebands and none in the carrier. At this point, any further increase in modulation would start taking
power from the sidebands and placing it back in the carrier resulting in a redistribution of power. |
|
|
Term
| In PM, what effect does the change in carrier frequency have? |
|
Definition
| None. The frequency change in PM is incidental. |
|
|
Term
Describe the effect the positive and negative alterations of a modulating signal have on the phase
of the carrier in PM. |
|
Definition
| During a 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? |
|
Definition
| During the constant amplitude part of the modulating frequency. |
|
|
Term
| What part of the modulating signal controls the amount of phase shift in PM? |
|
Definition
|
|
Term
| What part of the modulating signal controls the rate of phase shift? |
|
Definition
|
|
Term
| What is the advantage for using QPSK over BPSK? |
|
Definition
| QPSK has faster data rates, doubling the data carrying capability over BPSK. |
|
|
Term
| How can higher levels of PSK be achieved? |
|
Definition
| By using smaller phase shifts to allow for more phase shifts and increased capacity as each shift represents more bits in combination. |
|
|
Term
| The process of converting analog signals into digital signals. |
|
Definition
|
|
Term
|
Definition
| Band limiting, sampling, quantizing, and encoding. |
|
|
Term
| What is the main purpose of a band-limiting filter. |
|
Definition
| Ensures the input to the sampler never exceeds a maximum frequency. |
|
|
Term
| Converting a continuous time signal into a discrete time signal. |
|
Definition
|
|
Term
| What part of the pulse train is varied using PAM, PWM, and PPM? |
|
Definition
PAM = Amplitude
PWM = Width or duration
PPM = Position |
|
|
Term
| What is the Nyquist sampling rate? |
|
Definition
| Taking samples at twice the highest frequecy in the bandlimited signal. |
|
|
Term
| Which step of PCM assigns discrete amplitude values to the sampled amplitude values? |
|
Definition
|
|
Term
| The 2 methods of quantization. |
|
Definition
|
|
Term
| Which method of quantizing assigns amplitude values based on an equal amplitude range? |
|
Definition
|
|
Term
| With ATM, what is the length of each transmission unit? |
|
Definition
|
|
Term
What part of an ATM transmission tells the receiving device that a character is coming and that
the character has been sent? |
|
Definition
|
|
Term
| How does the receiving device determine whether it has received a correct character? |
|
Definition
| By summing the 1 bits. If the character arrives with an even number if 1 bits, the device assumes that it has received a correct character. |
|
|
Term
| What is an advantage of synchronous transmission over asynchronous transmission? |
|
Definition
| To reduce the overhead costs of data transmission. |
|
|
Term
| How does synchronous transmission differ from asynchronous transmission? |
|
Definition
| Synchronous transmission blocks many characters together for transmission. |
|
|
Term
| What does VRC check each incoming character for? |
|
Definition
|
|
Term
| What is the purpose of non-uniform quantizing? |
|
Definition
| To provide more coded amplitude levels at the low signal levels. |
|
|
Term
|
Definition
| A process that compresses the high-amplitude parts of a signal before transmission, decreas |
|
|
Term
| In LRC, what transmitted character does the receiver use to determine if a transmission was errorfree? |
|
Definition
| BCC (block check character) |
|
|
Term
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? |
|
Definition
|
|
Term
| How does the CRC method of error detection determine the dividend when computing the BCC? |
|
Definition
| CRC treats the binary ones and zeroes in the frame address, control, and information fields as one long binary number. |
|
|
Term
| How effective is CRC at detecting errors in most applications? |
|
Definition
| 99% in most applications. |
|
|
Term
| How does Automatic retransmit on request (ARQ) work? |
|
Definition
| The receiver automatically sends a retransmittal request to the sender if it finds an error in a received frame. |
|
|
Term
| Using forward error control, at which end of the transmission link are errors corrected? |
|
Definition
|
|
Term
| Using forward error control, what is the transmitter’s function in error correction? |
|
Definition
| To transmit multiple copies of the same messageto the distant end. |
|
|
Term
| Using forward error control, what is the receiver’s function in error correction? |
|
Definition
| To compare all copies of the same message to the distant end |
|
|
Term
| What are the three basic components that make up a fiber optics link? |
|
Definition
| An optical transmitter, a transmission medium and a detectoe or optical receiver. |
|
|
Term
| Name the three components that make up the optical transmitter? |
|
Definition
| A transmitter is comprimised of a driver, an optical source, a detector, and a FO pigtail. |
|
|
Term
| What are the three main types of light sources for optic waveguides? |
|
Definition
| LED, simiconductor laser diodes, and non-semiconductor laser diodes. |
|
|
Term
| Give the three main requirements of a light source |
|
Definition
1. Operating speed must fast enough to meed bandwidth requirements
2. Must provide enough optical power through the fiber to operate the detector.
3. It must produce a wavelength that takes advatage of fiber's long-loss propagation characteristics. |
|
|
Term
| What are the advantages of LEDs over lasers? |
|
Definition
| Small size, ruggedness, capability of single and direct modulation, reduce expense, spectral match with both fiber waveguides and silicon photodetectors |
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