Start Grob TV End Chapter Exercise 15
Answers are Underlined
Chapter 15
Cable Television
15-1
- a. The superband channel number just above VHF broadcast channel 13 is 23.
- b. VHF broadcast channel does a TV receiver with a cable converter stay tuned at 2, 3 or 4.
15-2
- a. The outer conductor of coaxial cable serves as a shield.
- b. Generally RG-59U cable is used for the drop line. T
- c. Thinner cable has greater losses. T
15-3
- a. The value of Resistance that was used to terminate RG-59U coaxial cable for impedance matching is 75 ohms.
- b. A line with more C per unit length has a lower Zo.
- c. Open ends of transmission line correspond to a parallel resonant circuit.
- d. The value of the VSWR when a cable is terminated in its Zo is 1.0.
15-4
- a. Cable losses increases at higher frequencies. T
- b. Coaxial cables have I2R losses.
- c. A 6-dB loss reduces the signal level by one-half.
15-5
- a. The head end of a cable system is the starting point of cable signals. T
- b. A trunk cable is the main line for cable signals. T
- c. The insertion loss is lower than the tap loss for line taps.
- d. A balun is used to match the 75-W coaxial cable to the 300-W receiver input.
15-6
- a. The reference level for the dBmV unit is 1 mV.
- b. The signal level of 2 mV in dBmV units is 6 dBmV.
- c. The signal level of 0.5 mV in dBmV units is –6 dBmV.
15-7
- a. Sync and blanking bars from another channel can be caused by overload distortion. T
- b. Losses increase with higher temperature.
- c. A slope-control circuit increases the amplifier gain for higher-frequency channels. T
15-8
- a. In two-way cable systems, the same cable for downstream and upstream signals.
- b. The upstream signal is in the band of 5 to 30 MHz.
- c. The poling signal is in the band of 107 to 119 MHz.
15-9
- a. The cable converter uses two local oscillators. T
- b. The video IF carrier in a cable converter is generally 612.75 MHz.
- c. The local oscillator for the up converter operates in the UHF range. T
- d. Each cable channel is selected by setting the frequency of the VCO for the up converter. T
15-10
- a. Wave traps to attenuate premium channels are usually located in the feed line to each subscriber.
- b. A scrambled channel usually has a picture that is out of sync, as evidenced by rolling and diagonal bars.
- c. A scrambles channel needs decoding pulses to restore the sync. T
15-11
- a. Supertrunks have the cable channels that are heterodyned down to lower frequencies.
- b. The frequency of 13 GHz is in the microwave band. T
- c. FM can be used for microwave links for television. T
15-12
- a. Fiber-optics cable has very low losses. T
- b. A light-modulated signal is limited to narrow bandwidth in the modulation. F
- c. Refraction means the bending of light waves. T
- d. Fiber-optic cable makes use of internal reflections of light. T
- e. Typical index of refractions: glass - 1.8, diamond - 2.4, water - 1.3
1. Which of the ff is a midband cable TV channel is A or 14.
2. Coaxial cable for distribution systems has an impedance of 150 ohms.
3. The cable converter output for the TV receiver is usually on channel 3.
4. A tap for the subscriber drop line has a high tap loss.
5. The most popular plug for the RG-59U coaxial cable is the F connector.
6. Which of the ff is true? Weak signal causes snow in the picture.
7. The upstream signal in two-way cable systems has the frequency of 5 to 30 MHz.
8. A typical value for the IF signal, in megahertz, for up-down cable converter is 612.75.
9. Frequency synthesis is used for the VCO in the up-converter.
10. For in-band descramblers, the decoding pulses are sent on the sound carrier.
11. A trunk cable run has a loss of –20 dBmV. To make up for this loss, the voltage gain of the next amplifier should be at least 10.
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