402 Electronic Communication and Data Systems
3. The __________ __________ stage correctly
shapes the sawtooth waveform for the horizontal
deflection coils.
4. What is the purpose of a shadow mask?
5. A Sony Trinitron color tube uses a(n) __________
aperture.
6. Each TV channel bandwidth is:
a. 6 Hz.
b. 60 MHz.
c. 6 MHz.
d. None of the above.
23.3 TELEVISION INNOVATIONS
In addition to the electronics of television itself,
there are a number of other electronic innovations that
have been created to work with television. A few of these
innovations are detailed here.
Video Cassette Recorders
Video cassette recorders (VCRs) can be used to play
videotapes. They also can be used to record and play back
television broadcasts.
Most VCRs have four heads. A video head is a tiny
electromagnet that reads information from the recorded
tape during playback. It writes information onto the tape
during recording. VCRs can have extra heads that provide
better sound and picture quality.
Look at Figure 23-19. Recording information on a
magnetic tape is simple. The tape is plastic with a thin
coating of iron oxide on one side. The iron oxide is a
6 MHz
4.5 MHz
4 MHz
0.75
MHz
71.75 MHz
66 MHz
72 MHz
Picture
carrier
Sound
carrier
Lower
SB
Upper
Sideband
67.25 MHz
Channel number Frequency band
(MHz)
14 470–476
15 476–482
16 482–488
17 488–494
18 494–500
19 500–506
•
•
•
•
83 884–890
Figure 23-16. VHF frequency assignments.
Figure 23-17. Shown are the locations of the picture
carrier and sound for channel 4, VHF. The channel is 6
MHz wide.
Figure 23-18. Examples of some ultra high frequency
(UHF) channels and where they are located in the
frequency band.
Electrical signal
input
Recording head
Iron oxide coating
on plastic tape
Magnetized patterns
on tape represent
electrical signals
Coil winding
Alternating
magnetic
field
Figure 23-19. Magnetic tape recording is simply impres-
sions of a magnetic pattern on an oxide tape.
Channel
number
2 54–60 55.25 59.75
3 60–66 61.25 65.75
4 66–72 67.25 71.75
5 76–82 77.25 81.75
6 82–88 83.25 87.75
7 174–180 175.25 179.75
8 180–186 181.25 185.75
9 186–192 187.25 191.75
10 192–198 193.25 197.75
11 198–204 199.25 203.75
12 204–210 205.25 209.75
13 210–216 211.25 215.75
Frequency band
(MHz)
Video carrier
frequency
Aural carrier
frequency