NTSC

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DIGITAL VIDEO
DV
NTSC
WHAT IS IT?
ATSC
ANALOG vs DIGITAL
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The Telecommunications Act of 1996   This act was
passed by congress and signed by the president.
One of its provisions requires all terrestrial TV
stations in the country to convert to digital
modulation. (Contrary to a persistent rumor, the
VHF channels will not be abandoned.)   The
deadline for this switch is February 17, 2009.
To stay competitive, all cable systems are
rapidly converting to digital, but there is no
deadline for that.   The pre-existing TV
technology is called analog. It is also called
NTSC (National Television System Committee),
which are the people who defined it. The NTSC
spec was created in 1946, updated for color in
1953, and updated for stereo in 1984. Both of
these updates were backward compatible, rendering
nobodys TV set obsolete. But the new digital
standard is totally different. The only thing it
has in common with NTSC is the 6 mega-hertz
channel width. To continue using an NTSC TV
after 2009 you might have to buy a converter box,
which will probably cost about 60. These boxes
are not yet available. You will not need such a
box if you can rely on a cable or satellite box
that has an NTSC output.   The new digital
standard is called ATSC (Advanced Television
Standards Committee). The government will
require that all new TVs be able to receive ATSC
channels. The ATSC standard includes multiple
formats from 640x480 pixels to 1920x1080 pixels.
All TVs must receive all of these digital formats
and display them suitably. The broadcaster
chooses the format.   To make the transition
gradual, the FCC is temporarily giving all
terrestrial TV stations a second channel, so that
they can broadcast a digital channel along with
their analog channel until 2009. There are 1700
terrestrial TV stations in the U.S. 1550 of them
have their digital channel on the air. Most
affiliates of the seven major networks (about
850) transmit some high definition programs.
Over 95 of the U.S. population can receive some
high-def programming from these stations. (These
numbers are as of December 2005.) The bad news
The cost to consumers of the new hardware. Home
TV systems may be especially complicated during
the transition. The picture-in-picture feature
many people enjoy will largely disappear as TV
set designers concentrate on more important
things, but it will eventually make a comeback.
NTSC images sometimes look worse on a big
high-def set than on a small standard TV.   The
good news The quality of TV reception will
improve dramatically. Temporary inconvenience,
permanent improvement.
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What exactly is ATSC? Advanced Television
System Committee is the name of the technical
standard that defines the digital TV (DTV) that
the FCC has chosen for terrestrial TV stations.
ATSC employs MPEG-2, a data compression
standard. MPEG-2 typically achieves a 50-to-1
reduction in data. It achieves this by not
retransmitting areas of the screen that have not
changed since the previous frame. Digital cable
TV systems and DBS systems like DirecTV have
devised their own standards that differ somewhat
from ATSC. Their high-def set top boxes (STBs)
conform to ATSC at their output connectors.
Most of these systems use MPEG-2. (DirecTV and
Dish Network are delivering systems that use
MPEG-4.)
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Bandwidth The bandwidth for NTSC is always 6
MHz. Without data compression, the bandwidth
for 1080i would be 300 MHz. With MPEG-2 data
compression the bandwidth varies according to how
fast the image changes. For 480i the bandwidth
rarely goes above 1 MHz. For 1080i and 720p the
bandwidth rarely goes above 3 MHz. Thus it is
possible to put six 480i programs or two 1080i
programs in a 6 MHz channel. The FCC allows
this. Thus terrestrial DTV stations have
sub-channels. It is up to the station managers
how many sub-channels to have and what
programming will air on those sub-channels.
Note that a sub-channel showing a static image
(e.g. a weather map or bulletin board) requires
almost no bandwidth despite being at high
resolution. ATSC is an imperfect standard in
that occasionally the bandwidth requirement will
exceed the channel size. When this happens,
the picture can get blurry or jumpy. Jumpiness
occurs when frames are deleted. Blurriness is
preferred because it is only momentary and often
not noticed. Transmission encoders have
improved gradually and hopefully will continue
to do so. In the future perhaps they will fail
in a completely unnoticeable manner.
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Which is better 1080i or 720p? 1080i and 720p
require about the same bandwidth when showing
live action A 1080i image has twice as many
pixels, while 720p shows twice as many frames per
second. While showing films at 24 frames per
second, 720p requires about half the bandwidth of
1080i. A common opinion is that 720p is better
for sporting events, while 1080i looks better
for documentaries, dramas, and most things that
come 24 frames per second. Unfortunately the
networks are picking one format for all their
shows. ABC, ESPN, and FOX have chosen 720p.
All other networks are using 1080i. Hopefully
some day they will choose the format according to
the content. 1080i and 720p are called High
Definition TV (HDTV). 480p is called Enhanced
Definition TV (EDTV). 480i is Standard
Definition TV (SDTV).
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TV channels are assigned a 6 MHz slot.
EXAMPLE OF AN ANALOG NTSC CHANNEL The
bottom edge of the over-the-air channel 2 is 54
MHz and the upper edge is 60 MHz. Within this 6
MHz space is a video carrier, a color carrier,
and an audio carrier. The frequency of the video
carrier is 1.25 MHz above the lower edge, so for
channel 2 the video is at 55.25 MHz. The color
carrier is approx. 3.58 MHz above the video
carrier so for ch 2 it is 58.83 MHz. The audio
carrier is 4.5 MHz above the video carrier, so
for ch 2 it is 59.75 MHz.
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ANALOG vs. DIGITAL Spectral display

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CURRENT CHANNEL ASSIGNMENTS
Channels 2 6 to be reallocated!!
Channels 60-69 will become the 700 MHz Band 
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8VSB HUH?
8VSB is the Transmission method for HDTV and
means 8-level vestigial sideband modulation
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Like traditional NTSC, the 8-VSB format utilizes
a vestigial sideband approach in the interest of
conserving spectrum space. Unlike NTSC, however,
8-VSB takes this concept to greater extremes
the lower RF sideband is almost completely
removed.                                       
                                                  
                                           
Hum!! Lets see, SSB carrier inserted.. SOUND
FAMILIAR?

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HD Radio???
It has been reported that as of June 2008, over
1,700 AM and FM stations are broadcasting with
HD Radio technology. Most of the stations that
have adopted the technology are FMs, while AM
stations have been slower to adopt the brand.
FM and Digital
Normal FM

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Sending pure digital data through the narrow 10
kilohertz AM channel is roughly equivalent to
sending data through an analog telephone line
(33.6k), thus limiting the maximum throughput
possible. By using Spectral Band Replication the
HDCSBR codec is able to recreate sounds equal
to or exceeding 15,000 Hz, thus achieving FM
quality on the bandwidth-tight AM band. The HD
Radio AM hybrid mode offers two options which
can carry approximately 40 or 60 kbit/s of data,
but most AM-digital stations default to the
more-robust 40 kbit/s mode which features
redundancy (same signal broadcast twice).
Currently, FM stations in the United States and
Canada are licensed to carry 130 kilohertz of
audio modulation bandwidth, requiring
approximately 260 kilohertz of RF spectrum. Only
15 kHz of the modulation bandwidth is used by
analog Monaural audio. Analog stereo uses 53 kHz
of space, and RBDS is centered at 57 kHz. The
"remainder" is currently available for other
services, including rental for secondary
broadcast services, paging and datacasting, radio
reading service, or as a transmitter-studio link
for in-house telemetry.
As with AM, FM stations may use separate exciters
to modulate the very different signals. A
combiner is often used, either before common
amplification or after separate amplification,
though stations are also now allowed to use a
separate transmitting antenna slightly higher or
lower on the radio tower. In each case the ratio
of power of the analog signal to the digital
signal is standardized at 1001. The 1 power
level of the digital signal from FM stations is
sufficient to approximate the coverage area of
the analog signal. Going forward, advances in
digital tuner design will create the scenario
where the digital signal coverage will probably
exceed the analog coverage due to the greater
potential ability to extract digital information
from a noisy signal.
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QUESTIONS???