Answers to Questions [Basic Color Television Course (1972)]

SECTION 1 ANSWERS

1. Electromagnetic waves

2. Same as 1.

3. Magnetic and electric fields.

4. Time and deviation (or amplitude)

5. In AM modulation, the carrier envelope is "expanded" or com pressed by another signal. In FM, carrier amplitude is held constant while the carrier frequency is varied.

6. Upper and lower chroma sidebands

7. Same as 6.

8. 12 VHF and 70 UHF, a total of 82 channels, each with a passband of 6 MHz

9. 54 MHz to 216 MHz, and 470 MHz to 890 MHz

10. By 57 and 147 degrees, respectively

11. Same as 10; burst is 0 degrees

12. V, 1.4 milliseconds; H 11.1 microseconds

13. Same as 12.

14. The vertical and horizontal blanking intervals

15. 75 percent; 12.5 percent; between 25 and 30 percent, round figures

16. H, 59.94 Hz; V, 15,734.264 Hz; C, 3.579,545 MHz

17. 15,734 kHz, the horizontal scanning frequency

18. Y equals 30 percent red + 59 percent green + 11 percent blue

19. See Fig. 1-10.

20. Above by 4.5 MHz

21. To avoid excessive standing wave ratios (SWR) that can mean reflected signals which cause images and picture ghosts and distortions.

22. The 3.579,345-MHz subcarrier oscillator

23. They compress sync pulses and video levels, causing vertical or horizontal rolling and often an overly contrasty picture that may even go negative. Audio will often buzz with IF amplifier overload.

24. Basically, it's a frequency discriminator-to-DC converter operating at a center frequency of 45.75 MHz.

25. Negative; better AGC control, 30 percent extra output power, noise in black region always less noticeable.

SECTION 2 ANSWERS

1. Brightness-picture shadings, the gray scale; hue-describes the actual color; saturation-the degree of color intensity.

2. Because it adds luminance to the primary red, blue, and green colors

3. More than 30,000; between 400 and 700 nanometers at frequencies ranging from 3 x 10^14 and 3 x 10^15 Hz.

4. All three unmodulated saturated colors

5. Anything; same as 4

6. NTSC and gated rainbow

7. R-Y and B-Y signals, like I and Q, contain green, too, and are 90 degrees out of phase when demodulated, so green-210 degrees from R-Y and 120 degrees from B-Y-is by no means a quadrature signal ana is not useful.

8. Same as 7

9. The color subcarrier xtal ; 0.0003 percent or 10 Hz in 3.6 million

10. Same as 9.

11. A field of non-contaminated color 12.

110 degree deflection angle; Chromacolor screen-in-line gun structure

13. A pattern of brightness variations appearing as sheer window curtains with overlapping folds. Actually, line-to-line variations as electron beams miss shadow mask holes. More prevalent because of better-designed tubes.

14. Dynamic convergence is already built in SECTION 3 ANSWERS

1. EIA color-bar pattern, and the vertical interval test signal ( VIT).

2. 195 divided by 80 or 2.44 MHz (something near the bandpass of many of the cheaper monochrome receivers).

3. High-frequency horizontal resolution

4. Ringing, regeneration, interference, receiver bandpass, etc.

5. The sweep-marker generator; f equals the number of lines divided by the sweep rate. However, you use this latter method only for very heavy input signals of millivolts to volts, which probably saturate the RF input.

6. To display the relative phase and amplitude of chroma signals on polar coordinates.

7. Look at both the EIA color bar broadcast pattern and the VIT signal.

8. Yes, when both are included in receiver controls; noise is adjusted first.

9. It fine tunes the local TV oscillator and can move a receiver's video, sound, and chroma response around on the response curve, causing much interaction.

10. No, Zenith's new solid-state set doesn't.

11. Vertical height and linearity, sometimes HV centering

12. Set for minimum of color snow in the raster on any blank channel.

SECTION 4 ANSWERS

1. One or more beams are not striking the color phosphors as they should.

2. Gun beams striking other than normal dots and in a weak magnetic field.

3. Back toward the convergence assembly.

4. Before

5. Before

6. To agitate and randomly orient magnetic lines of force in the metal shadow mask (demagnetize).

7. False; it increases

8. 100 percent

9. The screen cutoff points so all guns will extinguish at the lowest brightness levels.

10. Parabolic

11. Sawtooth

12. Two-pole convergence with red-green lateral magnets, simplifying red-green convergence.

SECTION 5

ANSWERS

1. Each marker is at 50 percent points on curve

2. The 41.25-MHz sound trap and 47.25-MHz lower-adjacent sound trap.

3. Same as 2.

4. Sound by 4.5 MHz

5. False. Almost all UHF tuners use semiconductors.

6. Positively not! The graph in Fig. 5-4A is substantial proof, at least from this manufacturer.

7. Low noise, adequate bandpass, good adjacent-channel sound rejection, low SWR, etc.

8. Selecting certain RF frequencies, then converting separate video and sound carrier to IF frequencies.

9. The internal generation (modulation of one by the other) of extra RF signals from two strong incoming signals.

10. Take your answer from Fig. 5-4. Of course, it is yes, since there's no filament, less heat, low noise, good gain, etc.

11. Basically, the turret tuner has channel strips mounted on a rotating drum instead of wafers, plus individually tuned RF and oscillator sections instead of series coils shorted by switches.

12. By application of DC voltages that make the diodes act like capacitors.

13. Amplifies video and chroma IF carriers for chroma, sync, and luminance processing by the rest of the receiver circuits.

14. Because of possible interference between it and the chroma in formation, which would cause chroma de-saturation in the picture.

15. See Table 5-2.

16. Rolloff.

17. Video IF, sound, and chroma (represented by sidebands)

18. No, because the LA trap is on the opposite side of the response curve from the 41.25-MHz sound carrier, at 47.25 MHz.

19. They consumed power, drew large currents, and would break down easier then less loaded resistors.

20. To achieve broader bandpass response and trap suckout.

21. RCA

22. This question is open to discussion. Consider the progress and multiple functions on a chip, then realize what the old systems did NOT do. Base your arguments on utility and not parts count; also, remember that the IC is mounted on a quickly detached module.

23. 1) No; 2) markedly. The RCA IC looks much different from the Motorola discrete component system.

SECTION 6 ANSWERS

1. White to the point of blooming.

2. In the absence of signals, the CRT is dark and there is no excess current drain.

3. No, and therein lies a problem.

4. So that chroma and luminance (fine detail) can be processed together when they are matrixed either before or in the picture tube.

Delay is 0.8 microseconds.

5. In circuit with a dual trace, triggered sweep, carefully calibrated oscilloscope.

6. In the luminance amplifiers.

7. It is cutoff

8. Nonlinearities that look like spurious voltages developed by nonlinear, half-wave diode video detectors.

9. By using a double-balanced, full-wave video detector; filtering is another.

10. 50 kHz to 150 kHz, a ratio of 3:1.

11. Foster-Seely discriminator

12. Yes, they're usually better designed and have excellent band widths.

13. Parallel, series

14. The outputs. The ratio detector output is a ratio change across the output resistors, while that of the discriminator is a voltage difference.

15. Its tuned quadrature grid causes larger or smaller current phase lags as a result of incoming signals which produce different pulse current widths at the detector plate.

16. Complementary symmetry output stage and capacitor coupling to the speaker.

17. Positive forward bias on the emitter, since its base is already biased on by R6 and R8.

SECTION 7 ANSWERS

1. To time the horizontal and vertical oscillators.

2. A diode. Today it's a separate circuit driven by the video amplifier and keyed into conduction by a pulse from the flyback transformer.

3. Low voltage, selected load and bias control.

4. Positively, and this early module control (it has since been eliminated) would cause the receiver to lose sync if it is not set correctly.

5. In microseconds, so the disturbance will affect only one part of a line.

6. Same as 7.

7. They show how exceptional IF amplifiers, if designed properly, can peak on weak signals in both video circuits and at the sound detector.

SECTION 8 ANSWERS

1. 1/59.94 Hz; two; 16.664 msec.

2. Interaction of linearity and size (height) controls, plus all around good linearity.

3. Trapezoidal waveform; a sawtooth

4. Resistors and capacitors

5. Because of its input DC-set RC time-constant and feedback from the vertical output stage.

6. Better frequency stability with temperature, small size, lower cost, and greater linearity with fewer components.

7. In Motorola it's 5.33 ohms at fo.

8. With a signal in, no signal out and DC voltages OK, substitute a complete IC for a cure if the grounds (chassis common) are secure.

9. C708, C709 SECTION 9 ANSWERS

1. They must have good hold and pull-in ranges, proper phase differences, little noise, good damping, and proper time constants.

2. At turn-off time when high voltages and currents coincide, causing the highest collector dissipation.

3. Horizontal repetition rate; because the raster is a 525-line system and all the lines must be generated in the time of one 30th second.

4. Yes. RCA uses a pair of SCRs, many use brightness limiters, there are HV doublers, triplers, quadruplers, and all these have smaller and in many cases unshielded flybacks.

5. They are RC series time constants in the control section of any horizontal oscillator to prevent over control when the receiver is warming up.

6. It is the anti-hunt network.

7. At 3/4ths of the rising forward scan.

8. Being a voltage-sensitive resistor, its resistance decreases with applied voltage and so reduces the grid voltage and the output tube's ability to conduct.

9. 1) Trace resonant, 2) Retrace resonant, 3) Power resonant

10. In RCA semiconductor sets, in parallel.

11. By cutting off its current, or reducing the anode-cathode voltage.

12. Same as 11

13. The retrace SCR conducts for some 25 microseconds, while the trace is on for only about 15 microseconds. This is because the trace moves the scan beam only about 38ths of the time, or 26 microseconds, vs 63.5 microseconds for retrace and blanking.

SECTION 10 ANSWERS

1. Have them oscillator driven and well-regulated.

2. To provide better current regulation and give the capacitive aquadag coating on the picture tube a chance to discharge. If it didn't discharge, a brightness spot would remain on the CRT long after the receiver was turned off.

3. To supply the deflection yoke with a linear sawtooth current to move the trace across the screen.

4. Absolutely not. The grid comes on first as shown in Fig. 10-3.

5. In the same direction.

6. It increases proportionally, if the control and circuit are linear.

7. Initially, it decreases, but then tries to increase. Certainly, if there's too much beam current without brightness limiting, there will be too much HV current drain and the flyback could go up in smoke.

8. How about the luminance amplifiers? A lot of service people always miss this one.

9. Oscillator drive of all voltage supplies, especially low voltage.

10. Center and amplitude.

11. The yoke current is shaped to linearize the sweep, not selective beam bending as with dynamic convergence.

12. Let R333 equal Rx, then:

10 = 200 x Rx x10 10^6+Rx 13.

10 x 10^6 Rx-1.990 x 10^3 5.03 x 10^3 = 5K = answer.

10^3 12 x 10^6 + 12 x 10^3 12-_ 12 x 10^3 166+ 10^3 10^3 E_in = 12 KV

14. Control beam current as a function of high voltage.

15. Magnetic flux

16. Replaced by the retrace SCR.

17. Due to the wider deflection angle of the 110-degree tube.

SECTION 11 ANSWERS

1. A set with a power transformer has isolation from house current; because it's less expensive than using a power transformer.

2. Through D1, which conducts on a negative input; D2 conducts on a positive input.

3. RMS x 1.414 equals peak, and 2 x 1.414 equals peak-to-peak. So 340 divided by 2.828 equals 120 volts, RMS, the usual receiver design center.

4. Less heat, reliable, maintain life efficiency, require smaller power transformers.

5. It becomes an AC shunt.

6. Voltages drop and AC ripple appears.

7. You don't! Only a totally open or shorted reactance can be accurately evaluated. You must use current, for instance, to evaluate electrolytic capacitors, or a capacitance checker, and a pulse voltage and an oscilloscope for inductors.

8. Base and emitter ( currents)

9. gm equals u/rp for the tube, while gm equals Id Vgs for the FET; AV equals gm x ZL which translates to gm equals AV/ ZL.

10. To comply with FCC regulations to disable part of the receiver in case the high voltage became excessive and threatens X-radiator.

11. By modulating the B+ supplied to the horizontal output trans former with a 60-Hz parabola.

12. By using regulators in the individual modules and not in the main supply.

13. AC all the way. If you missed this one, re-read the theory of operation twice! 14. The oscillator in Delco's is a 20-kHz free-running Colpitts instead of a "governed" oscillator at 15,734 Hz.

SECTION 12 ANSWERS

1. Color, burst, and flyback gating pulses

2. At or after the demodulators. In old-style receivers it is not used in the color subsystem. Instead, luminance is matrixed with chroma in the cathode ray tube.

3. Keeps the oscillator in color sync and somewhat controls the gain

4. Always externally

5. Down below the X axis in the fourth quadrant

6. 85, 90, and 105 degrees

7. In the cathode ray tube between control grids and cathodes.

8. From the negative outputs of the R-Y and B-Y demodulators across a resistive matrix.

9. No qualifications are required in the demodulation process to compensate for gray-scale tracking adjustments made solely in the luminance channel.

10. The 3.579,545-MHz chroma subcarrier.

11. 33 degrees

12. 3.08 MHz to 4.08 MHz; I and Q, since the R-Y and B-Y phase shift has not yet theoretically occurred.

13. The color killer 14. Traces of sync, slanting white lines, or flashes of color could appear on the CRT screen. One receiver with shorted vertical guide diodes even produces horizontal traces during this interval.

15. By the amplitudes of the demodulated RGB outputs

16. Injection lock; the sync burst rings the crystal directly.

17. It's a Schmitt trigger; one half is off when the other half is on.

18. Three, since ICI is a tri-phase demodulator.

19. Delivers more red to the CRT and changes the demodulator phase angle to include broader fleshtones.

20. Accu-Tint (RCA) 21. Preset (passive) brightness, hue, contrast, and intensity, while active semiconductors increase the red output gain, ride DC gain on the second color IF, and change the demodulator phase.

22. Switching, since the chroma is demodulated by 3.58-MHz switching at different phase angles.

23. No transformers to adjust, only 3 DC potentiometers

24. A color-bar generator and a vectorscope

25. Certainly. With no output from no. 1, there's no input to no. 2; therefore, no combined output.

26. No. A great deal of chemical and mechanical progress has been made since the original specification.

27. The latter. It's more expensive sometimes to generate, but it's also very reliable.

28. Be careful of neutralization and damping so the circuit has maximum transient response.

29. It will lock on a single cycle of burst.

30. "...out of phase with those opposite, so one pair switches while the other pair is off."

31. Differential amplifiers

32. A Schmitt trigger color killer

SECTION 13 ANSWERS

1. 1.5 percent

2. Shielded cable, preferably 300 ohms

3. No! Overall losses in all cables are greater at higher frequencies.

4. Make at least a visual inspection of the antenna and lead in.

5. Because of its characteristic impedance match with the receiver and the antenna. It should also contain the surrounding magnetic field in

its encapsulated sheath, and have the correct wire size and conductor spacing.

6. When you have seen the gain and lobe patterns and know the guaranteed strength in high winds

7. Normally, such an antenna doesn't exist.

8. See Fig. 13-1. They must be separated enough to avoid interference with each other.

9. They may turn or jump out of the connecting joints in high winds if you don't.

10. They last, look pretty, and you get more money for your installation.

11. No, it will absorb water and dirt, deteriorate, and lose signal and add ghosts. Furthermore, don't use ordinary twinlead except for FM radios.

12. Leading ghosts are normally found in installations close to the transmitter, while trailing edge ghosts are encountered in more remote locations-some distance, that is, away from the transmitter.

13. Use a fully shielded line and a directional, narrow front lobe antenna and a rotor, if at all possible.

14. 60 to 80 db.

SECTION 14 ANSWERS

1. Have a need where the instrument will pay for itself.

2. Perhaps to measure high voltage, current, and ohms. But there are even scopes by Tektronix that will do all these things and many more.

The realistic answer is no.

3. Digital multimeters, many of which already have astonishing accuracies, good ranges, and sell for less than $400.

4. Simply flip the AC-DC switch to DC and count the volts (determined by the number of graticule divisions) the waveform rises or falls.

5. Certainly, because at DC, the scope reads waveforms at peak-to-peak values anyway, just as it does on pulse voltages. And pulse voltages of certain repetition rates and durations are equal to DC voltages. Sine waves, however, must be divided by 2.828 to equal an RMS-DC calibration.

6. 2 to 5 milliseconds and 10 to 20 microseconds per division.

7. Yes, since it's taken at the AFC diodes. Sync information here is constantly correcting the horizontal oscillator.

8. The chop rate so far in oscilloscopes just isn't fast enough. Rarely does it exceed 150 kHz to 200 kHz, if that. So you'd see chopping "hash" all over the place and there would not be a useful signal display.

9. You might make a mistake among the changes, and this could put you in double trouble, not to mention the time wasted.

10. Not like the vacuum tube receivers where much of this trouble occurred in the horizontal output tube between grids and plate in the form of small but persistent oscillations. Semiconductor sets certainly develop faults-and some may look like Barkhausen, but they're really not.

11. 1) Saturable reactors; 2) solid state 12. Birdie, absorption, pulse and intensity.

13. Probably not, but a trap might be misadjusted or the fine tuning may not be right.

14. Probably not. The problem is associated with one of the video amplifiers.

15. You probably do need alignment. A test pattern or VIT signal would undoubtedly tell you right away.

16. Because you're using an oscilloscope as a real-time X-Y plotter and neither the receiver nor oscilloscope need vertical and horizontal sync. The sweep generator, however, does produce a 60-Hz sine wave for the X-amplifier terminals of the oscilloscope.

17. The double markers are the large ones and the f0 resonant frequency output is exactly between them.

18. The vectorscope can see only R-Y, B-Y; not G-Y and luminance.

19. Not always, especially if the positioning is critical.

20. Insufficient AGC bias, a bad cable connection or termination, or a bad sweep generator.

21. Find a common, secure chassis point, and make sure all equipment grounds meet at this point.

22. Turn off the line markers one by one and you'll know which ones to count on.

23. Not usually, and their frequency characteristics are lousy.

24. A triggered sweep oscilloscope with an accurately calibrated time base.

25. Because there may be trouble in a luminance amplifier instead, and you need to know if the tube emission is OK, whether it has shorts, and if its three guns track. A "gassy" tube might just turn up good. Of course, a gas check provision in the tube checker might help, too.

Also see:

TV Antennas and Transmission lines

Air Time--An Intro to Television Broadcasting

Video Handbook (1954)

TV and Radio Tube Troubles (1958)