Flashcards in nct 4 signals Deck (91)
The Cable TV System is also referred to what type of a system?
A Closed Loop System.
Within what part of the coaxial cable is the radioenergy is designed to be contained within?
The spot of damaged cable where the radio energy escapes into free space, transmitting (egress) and receiving (ingress) signals becomes what?
When a leakage is discovered, how do we isolate and locate the cause, make repairs, and verify that the leakage has been resolved?
By using radio receivers tuned to the aeronautical frequency band.
What must every system do to verify that there is no ingress above the power levels specified by the FCC?
Complete a proof of performance test and submit itsreport to the FCC periodically
What is the difference between a microvolt and a millivolt?
A Microvolt is unit of electric potential equal to one millionth (10-6) of a volt. A Millivolt (mV) is a unit of potential difference equal to one thousandth (10-3) of a volt.
Is the exponent or the power to which a fixed number (the base) must be raised in order to produce a given number.
How are Logarithms normally computed?
To the base of 10 and can therefore be defined as ‘The exponent of 10 required to equal the number.’
What is the log of 100?
The log of 100 is 2 (10 with an exponent of 2 = 100.)
What are Logs (logarithms) used for?
Is used for shortening mathematical calculations.
What’s an Exponent?
Is the number of times the base is multiplied by itself. (Example: 10 to the 2nd power = 100, 2 is the exponent)
What is a Base?
The number being raised. (Ex: 10 to the 2nd Power = 100, 10 is the base).
Any number raised to the exponent 0 is equal to what?
Any number raised to the exponent 1 is equal to what?
How does one multiply two or more numbers with the same base?
By adding the exponents.
How does one divide two or more numbers with the same base?
By subtracting the exponents.
What Prefix is a 10 with an exponent of 9?
What Prefix is a 10 with an exponent of 6?
What Prefix is a 10 with an exponent of 3?
What Prefix is a 10 with an exponent of -3?
What Prefix is a 10 with an exponent of -6?
What Prefix is a 10 with an exponent of -9?
What Prefix is a 10 with an exponent of -12?
if 256 QAM is employed the baud rate is how many bits per second?
Definition of Hertz
the System Of Units (SI) unit of frequency, equal to one cycle per second.
What is a continuous signal or carrier that varies in amplitude or frequency as a function of changes at its input?
An analog signal.
A non-continuous signal or carrier that changes its output in discreetly timed steps of voltage level and/or phase that can represent numerical values or other information.
Name 4 of the 8 advantages that digital transmission has over analog transmission:
1) No noise or distortion accumulation.2) High immunity to interference.3) Error checking may be included.4) Can be compressed and/or encoded.5) Easily stored and retrieved.6) Can be multiplexed and multi-layered.7) Unlimited copying or regeneration.8) Little or no loss of quality over long distances.
2 of the 3 disadvantages of digital transmission are:
1) Some loss of quality may occur in the conversion process.2) Added expense of digital processing devices.3) Digital terminal.
The basic Analog to Digital process includes what three steps?
1) Sampling2) Quantization3) Encoding
The term for the “measuring” of the analog signal at specific intervals is called:
What is the upside if more digital samples are taken for ADC?
The greater the number of samples taken, the more accurately the digitized signal will represent the originalanalog waveform.
What is the downside of additional samples for ADC?
A greater amount of bandwidth is required.
What is the the assigning of a specific value to each of the samples in ADC?
What is the process by which these specific values of samples are converted into a data or bit stream?
What type of noise can interfere with an analog signal and reduce its clarity?
Thermal or interfering noise.
What was our our earliest exposure to modulation?
An Analog Carrier Consists of what Three Carriers?
Video, Color, and Audio.
The digital carrier carries multiple channels. Thevideo, color, and audio carriers have been sampled, encoded, and converted into what type of streams?
What The five most common digital modulation schemes used today?
1) Amplitude Shift Keying (ASK)2) Frequency Shift Keying (FSK)3) Phase Shift Keying (PSK)4) Quadrature Phase Shift Keying (QPSK)5) Quadrature Amplitude Modulation (QAM)
One of the most basic digital modulation schemes in use:
Amplitude Shift Keying (ASK)
Describe the frequency and phase of the signal carrier of ASK:
It is constant but the amplitude is varied.
Why is ASK considered to be not a very useful or reliable data transmission scheme?
Because amplitude variations occur on most transmission mediums too frequently.
A carrier with an amplitude level of 10 dBmV or less, possibly even no carrier at all would represent what?
A carrier with an amplitude level of greater than 20 dBmV represents what?
Describe the amplitude and phase of the signal carrier of Frequency Shift Keying (FSK)
Amplitude and phase of the carrier are constant but the frequency is shifted to represent the difference between a one and a zero.
In the figure of frequency versus time in FSK, what does the higher frequency represent, and what does the lower frequency represent?
The higher frequency represents a “one” while the lower frequency represents a “zero.”
Defined as the position on a waveform cycle at a specific point in time.
Describe the amplitude and frequency of the signal carrier of Phase Modulation Keying (PSK)
Amplitude and frequency of the carrier are constant but the phase is shifted to represent the difference between a one and a zero.
The original form of PSK is known as what?
Binary Shift Keying (BPSK)
Binary Shift Keying (BPSK) provides how many bits per cycle?
When is the only time Phase changes in PSK?
When data changes.
What are the two Methods for Increasing Bits Per Second (BPS)?
1) Increase the frequency (number of cycles per second) of the carrier in ASK/FSK/PSK modulation to transmit more information (bits) per unit of time. The more cycles per second, the more changes per second can be achieved, thereby increasing thetransmission speed.2) Combine changes in amplitude, frequency, and/or phase of the carrier to get more opportunities to increase the data flow.
What are the two most common digital modulation schemes that use a combination of changes?
1) QPSK2) QAM
When modulation increases, the downsides are:
1) Greater susceptibility to interference2) Increase in channel power and total power3) Also produces and is susceptible to distortions
The two carriers in QPSK are called?
1) “I” (In-phase) 2) “Q” (Quadrature—shifted 90º or one quarter of a cycle)
The term for one of the more common network impairments describing unwanted outside signals entering the coaxial cable through cracks, breaks, loose connectors, poorly shielded drops, etc.
June 2009, full power TV stations have been requiredby the FCC to broadcast digital signals to eliminate what?
the possibility of ghosting due to ingress.
Name three symptoms of Ingress:
1) beats2) ghosts3) co-channel and/or electrical interference
What symptom of ingress is usually caused when the same channel from two (or more) different TVstations is received by the same antenna?
What is the term for identifying problems in the return path of the drop for ingress or egress?
What are two techniques for Pre-screening?
1) Scanning the drop externally with a leakage detector for egress of forward path signals.2) Connecting a signal level meter (SLM) capable of measuring sub-band frequencies to the drop at the tap or ground and scanning for any signals present. You can also use a spectrum analyzer for this.
Define term which describes a source of interference that affects the forward and return paths.
Common Path Distortion (CPD)
What causes of CPD?
When two or more carriers encounter a non-liner device, such as a connection where oxidation has occurred, harmonics and difference are produced.
What is the term for A chemical change caused by a reaction to oxygen, such as rust?
What is the term for component frequency of the signal that is an integer multiple of the fundamental frequency.
In CATV, what is used as the temperatureof reference?
68 degrees Fahrenheit (293.15º K)
Noise added to the response due to a lack of, or improper termination is called what?
Root Mean Square (RMS) is:
The square root of the arithmetic mean of the squares of a set of values.
Undesired changes in the waveform of a signal that occurs in its passage through the amplifiers of atransmission system are called what?
Name of 5 types of distortions:
1) Discrete Second Order2) Composite Second Order (CSO)3) Discrete Third Order4) Composite Third Order or Composite Triple Beat (CTB)5) Cross Modulation (XMOD)
Composite Second Order (CSO). Although a 12 log function, CSO is similar to CTB in that it is acombination of the amplitude and the logarithmic sum of the number of beats that fall in a channel that determines the level of interference. Of course, only those beats that fall into a visually susceptible portion of a TV channel’s bandwidth need be considered. The offending location is a group of beats 1.25 MHzand .75 MHz (± 15 kHz) above and below the visual carrier of the channel where the interference has occurred.
When two carriers, “A” and “B,” are applied to the input of an amplifier, the output of the amplifier will contain both the carriers plus their second harmonics (2A & 2B) and any combination of the sum and difference frequencies (±A ±B) that don’t result in a negative frequency.
Literally means the “crossing” of modulation from one channel to another.
Cross Modulation (XMOD)
Amplifier circuit paths that allow AC voltage to be directed onto specific distribution cables are referred to as what?
Power Passing Chokes
Hum Modulation appears as what on the TV screen
Appears as a horizontal bar in the picture.
Name 2 of the 4 Hum Modulation Solutions
1) Be sure that the power passing capabilities of the passive devices in your system exceed the maximum current that will be drawn through them.2) Take care if adding another amplifier to an existing AC power supply.3) If your taps are powering devices at the subscriber’s residences, the maximum potential current draw through the power passing devices from the power source must also be considered.4) A carrier-to-hum ratio of 30 dB or better (< 3% hum) is considered acceptable.
What is Hum Modulation?
Hum modulation is a low frequency signal level?
The FCC states Hum Modulation must be less than what percentage of the video carrier?
Most CATV systems carry what two things?
1) A Legacy Analog System2) A Digital Line-Up
Identify the 3 analog distortions that affect both the analog and digitally modulated carriers.
1) Carrier to Noise 2) Carrier to Coherent Interference3) Carrier to Low Frequency Distortion
What is the Carrier to Noise distortion?
The RMS level of the carrier to the thermal noise floor generated by the electronics.
What is the Carrier to Coherent Interference distortion?
Distortion components caused by non-linear mixing of carriers in the transmission system, which includes CTB and CSO.
What is the Carrier to Low Frequency Interference distortion?
Generally HUM at low frequency—60Hz from the power system, 120Hz from linear power supplies, < 1 KHz from switching power supplies, and other low frequency sources.
Name 3 of the 5 digitally modulated signals are affected by some unique impairments that minimally affect analog carriers:
1) Carrier to Sustained Impairments (CI) – Continuous unwanted signal within the channel pass band that can affect digital decoding but has minimal adverse effect on analog signals.2) Spectral Regrowth – Digital effect due to power loading on amplifier circuits, generally present in processing equipment.3) Multipath and Micro-reflections – In the analog world, this results in “Ghosting” or “fringing,” also known as “ringing.” These are reflections that, if high enough in level in relation to the carrier, cause digital decoding problems.4) Phase Noise – Generally has no effect in the analog world, but cancause severe reliability problems in digital carriers. This is usually due to oscillator instability in processing equipment.5) Amplitude and Phase Distortion – Result of the presence of any of the distortion components listed above that cause an error in the digital decoding.
What are Carrier to Sustained Impairments (CI)?
Continuous unwanted signal within the channel pass band that can affect digital decoding but has minimal adverse effect on analog signals.
What is Spectral Regrowth?
Digital effect due to power loading on amplifier circuits, generally present in processing equipment.
Define Multipath and Micro-reflections:
In the analog world, this results in “Ghosting” or “fringing,” also known as “ringing.” These are reflections that, if high enough in level in relation to the carrier, cause digital decoding problems.
Define Phase Noise:
Generally has no effect in the analog world, but can cause severe reliability problems in digital carriers. This is usually due to oscillator instability in processing equipment.
What is Amplitude and Phase Distortion?
A Result of the presence of any of the distortion components listed above that cause an errorin the digital decoding.
How is C/N measured?
With a Signal Level Meter (SLM), o spectrum analyzer.