Middleton W.M. (ed.) Reference Data for Engineers: Radio, Electronics, Computer and Communications
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TABLE
4.
NUMERICAL DESIGNATION
OF
TELEVISION CHANNELS
Channel
Band
Channel
Band Channel
Band
Number
(megahertz) Number
(megahertz) Number (megahertz)
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
54-60
66-72
76-82
82-88
174- 180
186-192
198-204
204-210
4 7
0
-
4 7 6
476-482
482-488
488-494
500-506
506-512
5
12-518
518-524
524-530
60-66
180-186
192- 198
2 10-2 16
494-500
530-536
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
536-542
542-548
554-560
560-566
566-572
572-578
584-590
548-554
578-584
590-596
596-602
602-608
608-6 14
614-620
620-626
626-632
632-638
638-644
650-656
662-668
668-674
644-650
656-662
48
49
50
51
52
53
54
55
58
58
60
61
62
63
64
65
66
67
68
69
674-680
686-692
692-698
704-710
7 10-7 16
716-722
734-740
752-758
758-764
764-770
680-686
698-704
728-738
746-752
770-776
776-782
782-788
788-794
800-806
794-800
The
frequencies
between
806
and
890
MHz,
formerly allocated to television broadcasting,
are
now
allocated to the
land
mobile
services. Operation,
on
a secondary basis,
of
some television translators
may
continue
on
these frequencies.
UHF television channels at different heights and pow-
ers. The F(50,50) curves are used for the prediction of
service, while the F(50,lO) curves are used for the
prediction of interference. Cochannel TV stations oper-
ating with offset carriers are afforded desired-to-unde-
sired interference protection of 28 dB, Le., F(50,50)
-
F(50,lO)
=
28 dB. The antenna height is the height of
the radiation center of the antenna above the average
terrain. ‘‘Average terrain” is determined by averaging
the ground elevations between
3
and
16
km
from the
antenna site, taken along eight radials separated by
45”
in azimuth. Effective radiated power is the product of
the antenna gain and the antenna input power. Antenna
input power is the peak visual output power of the
transmitter less transmission-line and diplexer losses.
The procedures to be followed in determining the
effective radiated power
used
in
the prediction of
coverage are detailed in Section
73.684
of the FCC
Rules and Regulations.
Directional antennas may be employed to improve
service. The ratio of maximum to minimum radiation in
the horizontal plane may not exceed
10
dB for channels
2-13,
and 15 dB for channels
14-69
if the transmitter
power is more than
1
kW.
There is
no
restriction for
channels
14-69
if the transmitter power is 1
kW
or less.
Transmission Standards-The standards for tele-
vision transmission in the
US,
as defined by the FCC,
are:
Channel Width:
6
MHz
Picture Carrier Location: 1.25 MHz
2
1000 Hz
above lower boundary of the channel.*
Aural Center Frequency:
4.5
MHz
?
1000 Hz above
visual carrier.
Polarization of Radiation: Horizontal normal, right-
hand circular optional.
Modulation: Amplitude-modulated composite pic-
ture and synchronizing signal on visual carrier,
together with frequency-modulated audio signal
on
aural carrier. (See
Figs.
15 and
16.)
Scanning Lines:
525
linesiframe interlaced two
to
one.
Scanning Sequence: Horizontally from left to right,
vertically from top to bottom.
Horizontal Scanning Frequency: 2/45 times chromi-
nance subcarrier frequency
(15
734
Hz).
Vertical Scanning Frequency:
2/525
times the hori-
zontal scanning frequency
(59.94
Hz).
Chrominance Subcarrier Frequency:
3.579 545
MHz
r10
Hz.
Polarity of Transmission: Negative-a decrease in
initial light intensity causes an increase
in
radi-
ated power.
Transmitter Brightness Response: For luminance sig-
*
Carrier frequencies may
be
offset
?C
10
kHz
(e.g..
1.24
or
1.26
MHz
above band
edge)
for
cochannel-interference
considerations,
-
BROADCASTING STANDARDS
35-13
3
cr:
3
Fig. 10.
Estimated field strength exceeded
at
50
percent
of
the potential receiver locations for at least
50
percent
of
the
time for
TV
channels
2-6.
Receiving antenna height,
9
meters.
After
FCC
Rules and Regulations.
nal, radio-frequency output varies in an inverse
logarithmic relation to the brightness of the
scene.
Aural-Transmitter Power: Maximum radiated power
is
22%
of peak visual effective radiated power.
For color transmission, the luminance component is
transmitted as amplitude modulation of the picture
carrier and the chrominance components as amplitude-
modulation sidebands of a pair of suppressed subcar-
riers in quadrature (Fig. 17).
The interval beginning with line 17 and continuing
through line 20 of the vertical-blanking interval of each
field may
be
used for the transmission of data, test
signals, and cue and control signals. Test signals may
include signals designed
to
check the performance of
the overall transmission system or its individual compo-
nents. Test signals or cue and control signals may not be
transmitted during that portion of each line devoted to
horizontal blanking. Line
19
in each field may be used
only for transmission of the standard vertical interval
reference
(VIR)
signal. Line
21
may be used for
transmission data such as closed captioning for the deaf.
Lines 10-20 may be used for data and text transmission
(Teletext) except as noted above.
Aural
Transmitter-The TV audio signal is fre-
quency modulated
on
a carrier
4.5
MHz above the
visual carrier. The power level of the carrier may not
exceed 22% of the peak visual power. The carrier is
35-14
REFERENCE
DATA
FOR ENGINEERS
3
cr:
2
3
Fig.
11.
Estimated field strength exceeded
at
50
percent
of
the potential receiver
locations
for
at
least
10
percent
of
the time
for
TV
channels
2-6
and
FM.
Receiving antenna height,
9
meters.
After
FCC
Rules and Regulations.
deviated 25 kHz for
100%
modulation, and the same
75-microsecond pre-emphasis specified for
FM
broad-
casting
is used.
A
multichannel television sound system
(MTS)
may be employed to provide stereophonic and
other audio services. The common system in use is the
BTSC (Broadcast Television Sound Committee) format
which provides a compatible
(L+R)
signal, a com-
panded stereo difference signal, a separate audio pro-
gram
(SAP)
channel, and a utility audio-data channel
(PRO
channel). Total aural baseband information must
be maintained within a
120-kHz
bandwidth.
Cable
Television
Cable television (CATV) systems were originally
called “community antenna television systems.
”
They
had their origin in mountainous regions of Pennsylvania
where “off-air” reception of broadcast television sta-
tions was difficult, if not impossible. Beginning with
crude antennas and amplifiers that delivered a few
channels to homes in sparsely populated valleys, CATV
systems have evolved into a broadband technology
utilizing high-capacity coaxial cables to carry signals in
the spectrum from
5
MHz to over
500
MHz and
fiber-optic cables with seemingly limitless capacity.
Some modern systems employ multiple cables for
separate subscriber and institutional networks, each
with two-way capability. Cable TV systems have devel-
oped into carriers of more than “off-air’’ programming
from broadcast stations. Modern urban cable systems
carry more television signals emanating from satellites
and local sources than from broadcast stations.
BROADCASTING
STANDARDS
35-15
Fig.
12.
Estimated
field
strength exceeded at
50
percent of the potential receiver locations
for
at least
50
percent
of
the
time
for
TV
channels
7-13.
Receiving antenna height,
9
meters.
After
FCC
Rules and Regulations.
Converters are used at subscriber locations to change
nonstandard channel frequencies to a standard VHF
channel (usually between
2
and
6
inclusive)
so
that
ordinary television receivers can demodulate the sig-
nals.
Most new receivers are being manufactured with
“cable ready” tuners capable
of
tuning more than one
hundred channels. The cable channel frequency assign-
ments generally used are given in Table
5.
Bidirectional cable systems normally employ a low-
band split (i.e., downstream channels above
50
MHz
and
upstream channels below
50
MHz)
or a midband
split with the division occurring near
150
MHz.
As
the
upper limit of usable cable-system frequencies increas-
es, the frequency where the split occurs has been
adjusted.
Cable systems are not regulated to any great extent by
the FCC,* and the technology has far exceeded the
minimum performance requirements set by the Com-
mission. Of particular regulatory concern, however,
is
the unwanted leakage from poorly constructed and
maintained CATV systems
of
radiations such as spuri-
ous signals in radio-frequency bands used for services
crucial to the safety of life. The Commission has
restricted CATV operation
on
frequencies which coin-
cide with aviation services
(108-137
MHz)
and other
governmental/public-safety
bands.
Some services delivered by CATV systems are tiered
to varying levels of subscription fees, and access to the
_I
*
FCC
Rules
and
Regulations, Part
76.
35-16
REFERENCE
DATA
FOR ENGINEERS
Fig.
13.
Estimated field strength exceeded
at
50
percent
of
the potential receiver locations for
at
least
50
percent
of
the time
for
TV
channels
14-69.
Receiving antenna height,
9
meters.
After
FCC
Rules
and
Regulations.
higher-level tiers is limited by the use of scrambled
signals and addressable converters and decoders. Newer
technology incorporates provisions
for
“pay-per-view’’
access to special-events programming.
One of the limitations on the number of channels a
cable system can carry is the distortion due to intermod-
ulation and cross-modulation products resulting from
system nonlinearities and the numerous carriers.
Com-
posite triple beat
is a term applied to third-* and
higher-order products, which can greatly degrade the
performance of a system. One method used to reduce
these effects is the employment
of
coherent oscillators
-
*
Products
of
the general type
(2f,
i
fi)
or
(fi
+
fi
f
A).
to regenerate (and convert) carrier frequencies such that
they are harmonically related
(HRC).
This intermodula-
tion problem increases with amplifier output levels and
builds as amplifiers are cascaded. This then becomes
the limiting factor
on
the length of a system (number of
amplifiers in cascade), and, as the number of channels
is increased, the amplifier separation must be reduced
to compensate for lowered output levels. Extension
of
systems and system interconnection into large networks
are also limited by this constraint.
Fiber-optic, or light-wave cable, systems are being
developed which promise to improve many of the
transmission characteristics of coaxial-cable (broad-
band) amplifier systems. While there are few operating
CATV systems delivering signals directly to subscribers
BROADCASTING STANDARDS
35-17
-40
I I I
1
I
I
I
30
50
100
200
500 1000
1600
TRANSMlTTlNG ANTENNA
HEIGHT
IN METERS
Fig. 14. Estimated
field
strength exceeded
at
50
percent
of
the potential receiver locations for at least 10 percent of the
time
for
TV
channels 14-69. Receiving antenna height,
9
meters.
Afer
FCC
Rules and Regulations.
via fiber optics, this technology is being employed to
deliver signals to headends or as “super trunks” to
deliver signals to multiple miniheadends in many sys-
tems. However, coaxial-cable hardware development
has advanced to the point where it has been the most
practical method
of
constructing economical broadband
systems; fiber-optic technology has emerged from the
developmental stage for this application, and greater use
will be seen.
As
this section was being written, the FCC had
initiated regulatory action which would permit tele-
phone companies to deliver video and wideband infor-
mation services. If these companies decide to get into
this business, they will employ fiber-optic systems, and
this could eventually lead to the installation of light-
wave capability into most homes and businesses for all
communications.
Other Television Services
Translators
and
LPTV-Television broadcast
translators and low-power television
(LPTV)
stations
operate under Subpart
G
of
Part
74
of
the FCC Rules
and Regulations.
A
television broadcast translator is a
station that rebroadcasts the programming
of
a broad-
cast station in an essentially unaltered form. The signals
from the originating station may be delivered by direct
off-the-air pickup, microwave relay, satellite transmis-
sion, or rebroadcast
of
another translator.
An
LPTV
station is similar to a translator station in terms of
35-18
I
PICTURE
CARRIER
I
CHROMINANCE
I
SUBCARRIER
i
FREQUENCY
0.5
SOUND
CENTER
FREQLIENCY
I
I
I
7.1
CHANNEL FREQUENCY SPECTRUM IN MEGAHERTZ
REFERRED
TO
LOWER FREQUENCY LIMIT
OF
CHANNEL
Field
strength at
points
A
shall
not
be greater than
-
20
dB
Fig.
15.
Radio-frequency amplitude characteristics of televi-
sion picture transmission. (Drawing
not
to
scale.)
equipment and service area, but it is permitted to
originate programming from virtually any source. The
technical rules governing translators and LPTV stations
are essentially identical.
For VHF stations, the transmitter output power (peak
visual) may be up to
10
watts unless the station operates
on an unoccupied channel assigned to its community for
regular television broadcast use; in this case, 100 watts
may be employed. A
UHF
station may be authorized on
any channel with transmitter power up to
1
kW.
There is
no limitation on effective radiated power for either type
of station. If stations employ circular polarization,
authorized transmitter power may be doubled for all
classes.
The technical standards for operation of these sta-
tions are generally the same as those for broadcast
stations (A5/F3 modulation) with the principal excep-
tions relating to carrier-frequency tolerances, spurious
emissions, and lower-sideband attenuation character-
istics.
Channel assignments are made on the assumption
that these facilities are secondary to broadcast stations
and must protect existing facilities from objectionable
interference. While the service area of a regular broad-
cast station is defined as the area within the predicted
Grade
B
contour, the service area of an LPTV station is
much smaller and generally equivalent to the area
within a predicted contour approximating its Grade A
service area. Existing LPTV stations are protected from
interference from newly proposed LPTV stations.
High Definition Television-High definition tele-
vision (HDTV) system proposals abound as of the
writing of this text. The FCC is considering various
systems through the Advanced Television System Com-
mittee and the Advanced Television Test Center. The
latter is conducting laboratory and field tests on the
systems, while the former group
is
dealing with the
development of HDTV transmission standards. A 1993
target date has been established for the completion of
the work. Major issues include compatibility of any new
system with existing NTSC systems, channel bandwidth
requirements, modulation (analogldigital), signal prop-
agation anomaly correction methodologies, and the
impact of emerging international standards.
ITFS-Instructional Television Fixed Service
(ITFS) stations operate under Subpart
I
of Part 74 ofthe
FCC Rules in the band 2500-2686 MHz. These
stations are licensed to eligible educational entities for
the distribution of program material
to
students enrolled
in instructional curricula. Public broadcast stations
rendering such services are also eligible. An additional
4
MHz (2686-2690 MHz) is assigned for ITFS re-
sponse stations. Response channels are intended for use
as return links to the originating point for aural infor-
Notes for Fig. 16:
1.
H
=
time from start
of
one line to start of next
line.
2.
V
=
time from start of one field to start of next
field.
3. Leading and trailing edges of vertical blanking
should be complete in less than 0.1H.
4. Leading and trailing slopes of horizontal blank-
ing must be steep enough to preserve minimum
and maximum values of
(x
+
y)
and
z
under all
conditions of picture content.
5.
Dimensions marked with an asterisk indicate
that tolerances given are permitted only for
long-time variations, and not for successive
cycles.
6. Equalizing-pulse area shall be between 0.45 and
0.5
of the area of a
horizontai-synchronizing
pulse.
7.
Color burst follows each horizontal pulse, but
is
omitted following the equalizing pulses and
during the broad vertical pulses.
8.
Color bursts to be omitted during monochrome
transmission.
9. The burst frequency shall be 3.579545 mega-
hertz. The tolerance on the frequency shall be
?IO
hertz with a maximum rate of change
of
frequency not to exceed
1/10
hertz per second.
10.
The horizontal scanning frequency shall be
2/455
times the burst frequency.
1
1.
The dimensions specified for the burst determine
the times
of
starting and stopping the burst but
not its phase. The color burst consists of ampli-
tude modulation of a continuous sine wave.
12. Dimension
P
represents the peak excursion of
the luminance signal from blanking level but
does not include the chrominance signal. Di-
mension
S
is the synchronizing amplitude above
blanking level. Dimension
C
is
the peak carrier
amplitude.
13.
Refer to FCC standards for further explanations
and tolerances,
14. Horizontal dimensions not to scale in
A,
B,
and
C.
BROADCAST1 NG STANDARDS
35-19
VERTICAL SYNC PULSE INTERVAL
EQUALIZING PULSE INTERVAL
71
~,
1
,,
EQUALIZING PULSE INTERVAL
HORlZOhTAL SYNC PULSES
710
075
t
0
02SIP
MAX. CARRIER VOLTAGE-
4
HI-
(SEE NOTES
3
AND
51
BOTTOM
OF
PICTURE
TIME
ZERO CARRIER
-
A
Fleld
1.
PICTURE
HORIZONTAL
BLANKING
B.
Field
2
t
10
075
t
0
025)C
(0
125
t
0
025lC
-TOP
OF
PICTURE
COLOR BURST (SEE NOTE
8)
C
Detoll
between
3-3
In
B
HORIZONTAL SYNC
BLANKING LEVEL
[SEE NOTE
3)
REFERENCE WHITE
ZERO CARRIER
I1
5s
11
10
OF
MAX BLANKING
OF
MAX
SYNC
,
D.
Detoll
between
4-4
In
B.
9/10
OF
MAX SYhC
8
CYCLES Mlh
0
125H
MAX
E
Detoll betueen
5
5
In
C
Fig.
16.
Television composite-signal waveform data. (See notes
on
facing page.)
REFERENCE DATA FOR ENGINEERS
Fig.
17.
Phases
of
color
signal.
matioddata such as student questions and responses.
These stations employ very low power and narrowband
equipment (250 mW at
125
kHz). The ITFS channels
are six megahertz wide and have a standard television
broadcast signal format. The channels are presently
grouped in bands of four alternately spaced channels
(e.g., group A is composed of A-1, 2500-2506 MHz;
A-2, 2512-2518 MHz; A-3, 2524-2530, etc.), with
adjacent groups interleaved as shown in Table 6.
Licensees are permitted to use multiple channels (up to
four) based
on
need and availability. Stations are
usually limited to an equivalent isotropically radiated
power (EIRP) of 33 dBw unless a directional antenna is
employed. The EIRP is further limited by coverage
requirements and considerations of interference to other
stations in the band (some “grandfathered” facilities of
other services remain in the ITFS band). The band is
also shared with the broadcast satellite service, and
protection to that service is afforded by the Rules.
Reception of ITFS signals usually requires the use of
a small parabolic antenna, which is coupled to a
down-converter. The down-converter incorporates a
low-noise front end (NF
<
5
dB) and converts the
signal(s) to VHF channels. A block of four channels
(group) can be converted in a single device to yield four
alternately spaced VHF channels (e.g.,
7,
9,
11, 13) or
wideband devices can down-convert all 31 channels to
VHF “cable” channels in a single block. Four-foot
antennas are generally used at distances up to ten miles
for received carrier-to-noise ratios of approximately
50
dB
.
MDS-The Multipoint Distribution Service (MDS)
is
a common-carrier service but is included in this
chapter on broadcasting because the service is used
primarily for the distribution of television program
material
to
subscribers (“pay TV”). It is governed
under Subpart
K
of Part 21 of the FC Rules. This
service
is
assigned 10 MHz of spectrum in the band
2150-2160 MHz, except in the top
50
market areas
where the band is extended
to
2162 MHz. Channel
1
has “inverted” carrier relationships (i.e., aural carrier
below visual carrier) with respect to channel 2 in order
to minimize adjacent-channel interference in those
locations where two channels are authorized. The band
2156-2160 MHz in smaller markets is too narrow to be
used for standard television picture transmission but
may be assigned for other purposes.
In all other aspects, MDS stations are very much akin
to ITFS stations, including hardware. As
in
ITFS,
reception is accomplished with a down-converter that
changes the 2-GHz signal to a standard VHF channel.
The higher power generally employed in the MDS
service permits the use of smaller receiving antennas
and higher-noise-figure down-converters, making home-
receiver reception practical.
The FC has allocated groups
E,
F, and H
to
the
MMDS (Multichannel MDS) service, which has
evolved into an “over-the-air” or “wireless” cable
service.
ITFS
licensees are permitted to lease excess
capacity
to
MMDS operators, thus increasing the total
channels potentially available to 3 1-33.
Network Distribution
of
Broadcast Program Signals
Terrestrial-Most network radio and television
programming formerly was distributed by terrestrial
microwave systems owned and operated by common
carriers (see Chapter 38). Television program transmis-
sion
is governed by the Network Transmission Commit-
tee Standard. NTC-7, which establishes reasonable
requirements for a system that is presumed to have over
100
microwave relay stations in tandem. While most
programming formerly was carried over facilities be-
longing to AT&T and other carriers, those facilities are
being supplanted by satellite-based systems. The princi-
pal advantage of the terrestrial system was its infrastruc-
ture which provided many routing alternatives; its
primary disadvantage was the poor performance of long
repeater cascades (coast-to-coast) as compared to satel-
lite transmission circuits.
Satellite Program Distribution-Space stations
in the Domestic Satellite Service are Seing used exten-
sively for the distribution of television programming.
Space stations are located in the geostationary (or
geosynchronous) orbit located approximately 23
000
miles in space above the equator. Satellites located
between approximately 70” and
145”
west longitude can
be “seen” from most sites in the continental
US
except
those
in
the most northerly latitudes. The Public
Broadcasting Service (PBS), was the first to distribute
its television Programming exclusively by the use
of
satellite channels; its sister organization, National Pub-
lic Radio (NPR), also distributes its programming
almost exclusively by satellite. Now virtually all net-
work TV program distribution is accomplished via
satellite.
When a satellite system is viewed as a point-to-point
microwave system with only one heterodyne repeater, it
is
readily apparent that vastly improved performance
can be obtained over the terrestrial system if carrier-to-
noise limitations can be overcome. With very-low-noise
amplifiers (30-50
K),
the weak signals from C-band
35-21
Freq.
Range
(MHz)
TABLE
5.
CABLE
TV
CHANNEL FREQUENCIES
Carriers
(MHz)
Video Color Sound
Channel
T- 8
T-
9
T-10
11.75-17.75 13 16.58 17.5
17.75-23.75 19 22.58 23.5
23.75-29.75 25 28.58 29.5
I
T-
7
I
5.75-11.75
I
7
I
10.58
I
11.5
i
T-12
T-13
2
35.75-41.75 37 40.58 41.5
41.75-47.55 43 46.58 47.5
54-60 55.25 58.83 59.75
I
T-11
I
29.75-35.75
1
31
I
34.58
I
35.5
1
5
6
76-82 77.25 80.83 81.75
82-88 83.25 86.83 87.75
1--3
I
60-66
I
61.25
1
64.83
I
65.75
I
27
28
29
I
4
I
66-72
I
67.25
I
70.83
I
71.75
I
240-246
241.25 244.83 245.75
246-252
247.25 250.83 25 1.75
252-258
253.25 256.83 257.75
I
7
~~
I
174-180
I
175.25
I
178.83
I
179.75
I
I
8
I
180-186
I
181.25
I
184.83
I
185.75
I