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What is the purpose of the equalizers in a CATV Amp?
Compensate for the cable loss
What can cause ghosts?
- Direct pick up of off-air signals by the TV receiver connected to the cable
- Poor return loss at the tap feeding the TV and missing end-of-line (EOL) termination
- A channel's reflected and direct signal picked up by the headend antenna
What is ingress?
Undesired signal(s) entering the cable plant
What may cause a "beat?"
- An unwanted carrier entering the system
- Co-channel interference
- Amp levels running several dB higher than specified
What is the proper way to write decibel-millivolt?
What might Cross modulation (Xmod) look like?
A stationary (or slightly moving) VERTICAL bar in the video portion of a channel carried on the cable system
What happens at the output of the last Amp if the imput and ouput levels of a cascade of Amps is raised by 3dB?
Carrier to Noise (C/N) has improved by 3dB and XMOD has degraded by 6dB
The signal level at the input to a tap is 32dBmV, you measure 15dBmV at the tap port. What is the tap value
What is potential difference?
The difference in Voltage between one point and another.
What is a conductor?
A substance that allows heat or electricity to pass along or through it.
What is polarity?
The direction of an electrical field in a radiated wave.
What are electrons?
Subatomic particles found in atoms that balance out the positive charge of a proton (within the nucleus) with their negative charge.
What is Alternating Current (AC)?
An electrical current, of which the polarity is periodically reversed.
A hertz is equal to?
One cycle per second (CPS).
What percent of electrical power in the US comes from AC power sources?
What are the four common waveforms encountered in CATV?
- Sine Wave
- Square Wave
- Quasi-square Wave
- Saw Tooth Wave
Where will you see Sine Waves?
When reading the voltage/current that feeds the home, powers your power supplies and TV channels that carry program info to the home
Where will you find a Square Wave?
Often found within the switching regulator DC output power supplies in Amps.
What meter is best used to measure Quasi-Square Waves?
a "True RMS AC Voltmeter"
What is the definition of Frequency?
the number of cycles of an AC waveform that occur in one second (CPS), and is called a Hertz (Hz).
What is the definition of a Wavelength?
the physical length of one cycle of the voltage waveform.
What is the formula to find a wavelength?
Wavelength = speed of light/Frequency
What is another name for the peak value of an AC waveform?
An AC's Amplitude
How is Ohm's law formula written?
R = E/I, where R is Resistance, E is Volts and I is current in Amps
What is the "skin effect?"
The difference in loss using the equation: the ratio of cable attenuation at two discrete freq is approx equal to the sq root of the ratio of the two freq.
What is Unity Gain?
A design philosophy wher ethe loss of the cable and other passice devices before an amp station equal the gain of the amp station
What is the Coax Attenutaion/Frequency Formula?
- AFN/AFO=√FN/FOWhere AFN is the loss in dB at the New Freq
- AFO is the loss in dB at the Old Freq
- FN is the New Freq
- FO is the Old Freq
- The 0.143 takes into account the higher dielectric loss at higher freq
What is a sweep response?
A representation of the network's response to a sweep signal and the effects of all the network components such as cable, connectors, passives, and signatures added by the amps.
What is tilt?
The difference in cable attenuation or amp gain between lower and higher freq on the cable network.
What is a slope?
The difference in gain between the ends of a band of frequencies.
What is roll-off?
A gradual or sharp attenuation of gain (Versus frequency) at either or both ends of the spectrum.
What is suck-out?
A sharp reduction in the amplitude of a narrow band of frequencies within the networks overall freq responses.
What is an Amplifier?
An active device used to increase the level of an input signal. Used in a cable system to compensate for the effect of attenuation caused by coax cable and passives
What is a pad?
A small plug-in device used to attenuate signals to correct operating levels.
What is an attenuator?
A device used to reduce signal strength.
What is an equalizer?
In a cable amp it is typically a small, plug-in device used to compensate for the fact that cox attenuation varies as the square root of freq.
What are signatures?
The effect a particular type of amp has on the overall freq response.
What is peak to valley?
The difference, in amplitude, between the most positive (peak) and the most negative (valley) levels of an electrical signal.
What causes diagonal lines on a TV screen?
Ham and other broadcast AM carries that cause interference.
What causes LEAD ghosting?
direct pick-up (Off air signal getting into the cable system viewed on the right of the image) while a following ghost is usually caused by signal reflection.
What is a ghost?
outline or multiple images of the primary TV picture to either side.
What causes FOLLOWING ghosts?
Usually caused by signal reflection (viewed on the left side of the image).
What causes co-channel interference?
Usually caused in one channel by the carrier from another transmitter operating on the same channel.
What is the definition of a beat?
The unwanted sum and/or difference freq resulting from the heterodyning (mixing) of two or more signals.
What is zero beat?
A method of reception using an RF current of the proper magnitude and phase relation so the received voltage is of the same nature as the original wave.
What are sparkles in the picture caused by?
Power line arcing, lightning, electric motors, automobile ignition and other sources of high-rise time energy entering the cable system from the tap up to and including the TV receiver.
What is Common Path Distortion (CPD)?
Interference in the return path signals caused by the reasction of the dissimilar metals, round in active of passive devices, to a combination of the oxidation process and the forward electrical signals.
What is absolute zero?
A theoretical temp equivalent to the absolute absence of heat and equal to -273.15oC or -459.67oF.
What is termination noise?
Noise added to the response due to a lack of, or improper temination.
What is Boltzman's Constant?
The proportionality constant that relates temp and bandwidth to power. 1.38x10-23.
What is the formula for calculating the noise produced in a 75-ohm resistor?
- En=Electromotive Force or RMS noise voltage
- k=Boltzman's constant (13.8x10-23)
- T=the temp in degrees Kelvin
- B=bandwidth in hertz
- R=resistance in ohms
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