Chapter 23 Television and Video Display Units 403
Electron
beam
Electron
gun
Phosphor-coated
internal screen
(red, blue, or green)
Image projected
to 4 1/4 5 2/3 feet
screen
Corrector
lens
Spherical projection
mirror
Infrared coded beam
Infrared receiver
Infrared transmitter
Remote
control
Digital
decoder
Figure 23-22. Projection tube for a large-screen
television.
Figure 23-21. A television remote control sends digital
information to the infrared receiver mounted on the TV.
magnetic material. The voice or picture message is con-
verted to electrical impulses. These electrical impulses
are applied to the coil winding on the recording head. The
fluctuations of the electrical impulses make the magnetic
recording head fluctuate at the same rate as the electrical
impulses. The magnetic head induces a magnetic pattern
on the metal-oxide tape. The magnetic patterns uniquely
match the original voice or picture patterns.
The videotape not only records voice and video but
also speed information, end of tape location, copyright,
and anticopy coding.
Digital Video Recorder
A digital video recorder (DVR) combines computer
and television components to form a television receiver. A
DVR receives a television signal and can record the tele-
vision program as well. A hard disk drive is used for the
recording medium rather than magnetic tape as found in
a VCR system. A hard disk drive is capable of recording
and storing hundreds of hours of television programming.
See Figure 23-20.
Remote Control
A remote control is an application of infrared light
and digital techniques. When a button on the remote con-
trol is pushed, a digital code is sent out of the remote con-
trol to an infrared sensor on the TV. The sensor on the TV
amplifies and decodes the signal. See Figure 23-21.
Large-Screen Projection TV
Most large-screen projection TVs use a special elec-
tron gun assembly that projects three separate images
onto a screen. Early projection TVs had screens with a
significant curvature. As these televisions became more
popular and more advanced, engineers were able to
develop a flat screen projection. Figure 23-22 shows how
the electron gun is assembled.
The main performance problem with large-screen or
projection TVs is the loss of clarity of the video image.
Remember there are only 525 lines per frame of display.
As the picture is increased in size, the lines become a dis-
traction. The image does not magnify; it simply gets
larger. Some large projection TVs offer a slight improve-
ment in video image by scanning the same lines twice for
a total of 1050 lines across each frame. These sets do
have a sharper, more appealing video image to the human
eye, but no real magnification has taken place.
Figure 23-20. A digital video recorder (DVR) with its
case removed. The hard disk drive is located in the cen-
ter of the device under the metal support. To identify the
hard disk drive, look at the thicker red cable.