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Larry Bloomfield & Jim Mendrala
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19, 1999 DTV Tech Note - 027
Published when any of us have something to share
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Subj: DTV Express and DTV Utah
From: Ed Williams - PBS
The DTV Express
was in Salt Lake City the last week of February. DTV Utah folks
had just been to see the FCC re their local plan and it was well
received. They take an interesting approach: Eight stations on non
adjacent channels alternately on two antennas with four to each
antenna. Cost for each station is well less than if each station
their own DTV
installation. KUED had made arrangements with Harris to have an
experimental DTV station on channel 40 for demonstrations during
our visits. Folks in several TV retail stores were watching....
and calling us when we were making adjustments to the system which
caused some temporary outages. KLS took their field measurement
truck around town to check on signals. Nice demo. They sure have
a problem with LPTV and translators tho. Took some of the best channels
for their main DTV signals and now must move many of the secondary
users. I expect DTV translators will be easy and cheap to implement.
Lower in power and able
to be put on
first adjacent channels in some cases through same antenna and line,
the costs should be acceptable. More on this later.
(Ed. Note: Ed Williams asked if we’d do
a hyperlink to the DTVExpress (dtvexpress.org) and have a list of
where their tour will be. No problem, we’ll run the list,
but some or our subscribers e-mail service can not accommodate attachments
or hyperlinks, so we don’t do that. The ball is in Ed’s court.)
PBS -- Tel: 703-739-5172 -- Fax: 703-739-8114 -- email: email@example.com
In response to
Anonymous in Burbank (Tech Notes # 25 & #26 )
Peacock Changing Colors?
The networks aren't the only game in town
anymore. Most of the money is being spent on programming like ER
which cost's "too much money per episode". As far
as technical quality, if the masses are not annoyed by a picture
that has been compressed down to nothing, why not do it? A cable
network operates on a budget that is a fraction of what NBC spends
and as far as the viewer is concerned the picture looks the same.
The bottom line is there isn't lots of money to be spent anymore.
A reasonable profit would be acceptable, but the other networks
are losing money and we are not far behind. As far as NBC being
sold, Bob Wright himself said that he wouldn't know how to go about
selling just the network and then who would buy it? A merger
is more likely. Television networks will never be what they
once were there is just too much to do out there technologically
these days and they had better find their new niche fast or face
(Note: This is a good simplified piece
that can help engineers explain to non-engineering types what’s
happening. There’s also a lot of engineers who could stand the refresher.)
Subj: What is HDTV and what does it
By: Jim Mendrala
all know that High Definition Television (HDTV) is television with
a lot of detail and an image in a wide aspect ratio. Let's break
What the camera is required to do.
What the broadcaster is supposed to do.
What the digital television (DTV) set does.
camera's lens focuses an image on to three CCD arrays. One for the
red, one for the green and one for the blue. We all know this because
that's the way it works in standard SDTV television. The major difference
between a SDTV and a HDTV camera is that the aspect ratio in a SDTV
is 4x3 (1.33:1) whereas in a HDTV camera it is 16x9 (1.78:1). Because
of the desire to have photographic quality pictures, the HDTV camera
has to have a lot more resolution than the SDTV. Lets compare.
of scan lines: 525
of active scan lines: 480
line time: 63.5 usec
pixels: 480 x 850
360 x 480
of scan lines: 1125
of active scan lines: 1080
line time: 29.6 usec
pixels: 1080 x 1920
720 x 1280
rate in both cases is 30 fps. If we lower the frame rate then the
same amount of spatial picture information will lower the bandwidth.
If we increase the frame rate, we will need an increase in spatial
bandwidth. For example, HDTV at 30 fps requires about 30 MHz of
bandwidth. 24 fps however only requires 24 MHz of bandwidth to get
the same picture quality per frame.
cameras scan the image in an interlaced mode, that is the even lines
first and the odd lines second creating two fields of information.
Since most cameras have no shutter the images come out as field
one (the odd lines) and field two (the even lines). Any movement
during each field is faithfully recorded with half the number of
active scan lines. In the case of SDTV 240 x 850 with a resolution
of 180 x 480 and for the HDTV 540 x 1920 and a resolution of 360
x 1280. The rows of the CCD sensors in the camera are usually to
produce an image free from aliasing artifacts between fields. In
the new 24p, 30p and 60p cameras, an optical low pass filter (O-LPF)
rids the image of aliasing artifacts.
the new 24p cameras, just like a Telecine, the image is progressively
scanned one frame at a time in 1/24th of a second. Generally an
electronic shutter with a exposure time of 1/48th of a second or
less is needed so that the image doesn't look to soft from motion
blur on moving objects. If the shutter time is too short than strobing
of the image will become apparent like in animated cartoons.
film on a Telecine is always progressively scanned. The image was
photographed on the film in typically 1/48th of a second 24 times
a second. The shutter closes and for the next 1/48th of a second
the film mechanism moves the next unexposed film frame into position
and readies it for the next 1/48 second exposure. The image then
can be progressively scanned and output as two fields. Combining
these two fields in a frame buffer puts the progressive frame back
together. This is known as 48sF or 48 sequential frames. This is
what the new 24p recorders do internally. They record two fields
derived from the progressively scanned image that was captured in
1/48th of a second.
all know the cameras used in the digital domain have to convert
the analog images on their sensors to a digital signal. This is
done by an Analog to digital (A/D) converter. The output than is
either a serial or parallel bit stream. This combined with audio
and data is what the broadcaster transmits. The digitized pictures
and audio are compressed and are put into digital packets. The packets
also contain data and header information to tell the DTV receiver
what type of signal it is, and how it might be handled. Display
of these packets is left up to the DTV receiver. Panasonic's DTV
receiver, for example will output any picture at 480p only, 1080i
only or any of the formats in Table 3 of the ATSC.
order to transmit all of this information within the 6 MHz channel
the Moving Pictures Expert Group (MPEG) invented a compression scheme
MPEG-2. It systematically allows the massive amount of information
to be honed down to fit into the 6 MHz available to the broadcaster
and is transmitted as an 8 vestigial sideband RF signal (which is
an analog signal, by the way).
the information to be transmitted is digital it is converted into
packets of video, audio, data etc. Therefore it doesn't matter what
the frame rate or what the aspect ratio is.
NTSC the image must be an analog signal, must have a 30 fps frame
rate and must be 2:1 interlaced as that is what the NTSC receiver
can only handle. (Because of the sound carrier being 4.5 MHz above
the visual carrier. To eliminate moir+d+k-n the picture, the frame
rate was lowered from 30 fps to 29.97 fps (frame rate x 1000/1001).)
In DTV, it doesn't matter what the frame rate
is or what the numbers of scan lines are as long as you can compress
the information into the 6 MHz channel. Since SDTV has a much narrower
bandwidth requirement, several SDTV channels can be transmitted
on one DTV channel. The limit to how many is determined by the amount
of degradation to each sub-channel that is acceptable. An
HDTV signal has a much higher bandwidth requirement so only one
HDTV or possibly one HDTV and one SDTV channel can be transmitted
on one channel at the same time.
the DTV receiver the incoming packets of information are received
and based on how the packets are packaged, the DTV receiver can
then display that image on its native display at whatever frame
rate works. The native display could be, for example, a Panasonic
480p DTV set and converts everything to 480p at 60 fps progressive
or with 48 fields on an interlaced native display. A Sony HDTV Trinitron
DTV receiver would display everything at 1080i at 30 fps with 60
field per second.
do this with 24-fps material, the receiver would convert to 30 or
60 by adding the 2:3 pull-down sequence to the video information
or in other words display each frame 3 times at 72 fps. This is
great news for we no longer are tied to the display device, specific
frame rates or aspect ratios.
the 16 x 9 (1.78:1) aspect ratio results in the smallest amount
of “letter-boxing” for all active aspect ratios from 1.33 (4 x 3)
on up to 2.35:1 (scope).
the broadcaster still wants to transmit the same images to his NTSC
transmitter. The NTSC transmitter can only accommodate a 30 fps/60
fields 1.33:1 aspect ratio and without any additional compression
a maximum of 4.2 MHz of picture information. Interlacing of the
image and the reduced bandwidths of the chroma channels are two
forms of compression.
Does HDTV look like?
far, all of the DTV receivers of today are deficient in the resolution
domain. Yes most have 1080 scan lines and a greater than 20 MHz
video bandwidth but there is more to the resolution issue. The most
critical is the electron beam's spot diameter. These are the beams
that are magnetically focused, deflected and are used to excite
the three phosphors, red, green and blue.
issue is dot pitch or the aperture grill. In an 800 x 600 14-inch
diagonal computer display the dot pitch has to be less than .02
inches or .51 mm. Now I'm referring to the native display of the
CRT tube not the number of scan lines that are on it. The number
of scan lines for this display has to be at least 600 to give it
about 400 lines of resolution.
you are looking at a 34-inch diagonal HDTV DTV set then that screen
is going to be approximately 17 x 30 inches. If you display the
scan lines so that they just touch each other, the spot diameter
would have to be 1/1000th of 17 inches or 0.03 inches. Most 35-inch
CRTs, with a 1.33 aspect ratio, today have a spot diameter of about
0.04 inches. This yields a maximum resolution of just about 350
lines. That's very different from the 720 lines of resolution with
1080 scan lines. The picture then tends to look soft compared to
a 480-scan line image with about the same resolution. Overlap of
the scan lines reduces resolution in the vertical. Bigger spot diameter
does the same thing in the horizontal, reduces resolution and smoothes
over detail. Remember the spot has a bell shape to it. It is not
a hard edge spot. It is brighter in the middle than at its edges.
With electron beam overlap, the display brightness tends to increase
up to a point. With space between the scan lines, the scan lines
themselves become visible and the picture looks apparently sharper.
eye can see more detail in the horizontal then in the vertical.
To prove this to yourself look at you're present TV from a distance
where the scan lines just blend in. Now tilt your head 90 degrees
and you will again see the scan lines. This is because of our stereoscopic
vision. We need to detect the vertical edges (horizontal scan) for
the brain to give us the sense of depth perception. The eye is constantly
vibrating back and forth a minute amount to help distinguish the
vertical edges of what's in front of us.
some of the new display technologies start showing up the displays
will take on a much better look. Texas Instrument's (TI) Digital
Micromirror Device (DMD), as an example, with 600 x 800 pixels would
give a resolution of about 400 x 500. If TI ever came out with a
DMD of 1080 x 1920 pixels the resolution of that display device
would be about 720 x 1280. As a point of reference that's about
40% of what a 35 mm academy aperture film resolves.
looking at the various HDTV sets, keep these things in mind. The
salesman will tell you the marketing propaganda with little technical
specs. As you can see line doubling or quadrupling yes makes a smoother
(soft) picture at the sacrifice of resolution unless the electron
beam is smaller and doesn't overlap. If interlaced then to eliminate
interline twitter the repetition rate must be at least 60 or better
especially if the display is very bright.
too that "You ain't seen nothing yet" when watching a
HDTV DTV broadcast. Display devices of today won't let you see all
the detail. When display technology improves the screen size in
the home most likely will grow to 4.5 ft. x 8 ft. That's not only
a big screen by today's standards but also a wide screen. You will
be able to view the screen from the same distance you now view your
27-inch TV set.
HDTV takes off then reduced resolution SDTV pictures will only be
okay on the smaller screens with 34 inch or less diagonal.
hope this helps in understanding where HDTV is today and where it
will go in the future. I'd like to hear some comments and/or questions
regarding the three areas discussed.
Subj: Television and the NAB
By: Larry Bloomfield
The annual gathering of the broadcast clan, under
the banner of the National Association of Broadcasters, is just
around the corner. Broadcasters, vendors and an interesting
assortment of other folks will descend on what has become the de
facto point of confabulation for the broadcast industry, Las Vegas,
Nevada. Television, the largest part of this whoopty doo,
hasn't always been a part of NAB.
NAB was formed as a group for radio broadcasters
in early 1922. It's kind of interesting to compare the attitudes
of the "then broadcast industry" about this new "upstart"
television to how many now feel about the onset of digital television
today. Despite the fact that many of television's early engineers
came from radio, as television emerged from the laboratories, it
was a curiosity. Despite this, the NAB was dominated by AM
radio interests who weren't happy about TV's encroachment.
Back in early 1940, Fred Wolcott, Technical Director
of Gilfillan Brothers and Irwin Stanton of RCA discussed the desirability
and need for an organization that would further the interest of
television both locally and nationally. As early as the 40s there
were enough people actively working in television to make it a reality.
Harry Lubcke, Director of Television for the Don Lee Broadcasting
System since 1931, and recognized for his pioneering efforts even
in those early days, was contacted by Wolcott and Stanton to assist
them in laying the ground work for the establishment of the Society
of Television Engineers (STE).
STE, which first met in July 1940, had a charter
membership that reads like a "Who's Who" out of
a television-engineering history book. Their stated aims and
purposes, which have remained unchanged through the years, are:
"To advance the theory and practice and to enlarge the use
of television and to promote harmony and cooperation within the
The STE played a very major roll during its early days in proposing
the NTSC standards. Remember this was way before Color. STE
enlisted the support of the industry and as the result of their
efforts, the NTSC standards became effective on April 30, 1941.
It was during this effort that they concluded that the television
industry needed of a national organization, within which industry
differences could be resolved so that a united and harmonious front
could be presented to government agencies.
In June 1943, Klaus Landsberg, Chief Engineer
of Television Productions, Inc., a Paramount Pictures subsidiary,
was asked to contact television and allied industries leaders, as
a representative of STE to explore the possibilities for such a
"national" organization. Because of the overwhelming positive
response to Landsberg's efforts, the constitution for a new, national
organization was unanimously adopted by STE at their August 1943
meeting forming under the name of The Television Broadcasters Association
(TBA). The first organizational meeting of TBA was held at
the Palmer House in Chicago, IL on Jan 17, 1944.
Content the formation of the TBA would carry
on the original goals and objectives on a national level, STE withdrew
Despite the many pressing wartime activities of the STE
membership, those early members took the time to continue holding
monthly meetings throughout the war years, in the interests of television.
The time for television to be a part of the NAB
was still down the road. The "Television Digest
and FM Reports," in their April 30, 1949
issue said that the TBA is "a small but cohesive alliance of
telecasters and major TV manufacturers decided ….. to go it alone."
But time changed attitudes. Within two years, in a mailing
entitled "News from NAB" it was reported from Chicago,
IL that, "A new autonomous television organization to operate
within the structure of the 29-year old NAB was formed here today."
A few days later Broadcasting-Telecasting reported
the "formation of a completely autonomous NAB-TV, operating
under the aegis of NAB, but to act as its own court of last resort,
was unanimously voted."
Paul Raibourn of KTLA was the chairman of TAB's
committee to study the feasibility of a single trade association
under NAB auspices. The voting took place only after various
segments of the TV industry were assured that autonomy could only
be achieved under NAB if each segment was its own court of last
resort. Raibourn was quoted as saying, "that having achieved
the autonomy it desired, TAB will in the near future wind up its
affairs. Not even two weeks later "Television
Digest" reported that the NAB would become the
NARTB in April 1951. It further reports that the Television
Broadcasters Association (TAB) will be dissolved and its manufacturer
members urged to join NARTB as associate members." On
Jan 1, 1958, the NARTB changed its name back to NAB completing the
If you're ever in Los Angeles on the 3rd Thursday of the Month,
except during July & August, the STE still meets. Just
ask most any Television Chief Engineer in the LA area and he'll
tell you the time and place. There's still interesting folks
and a good program and tell 'em, Larry sent you.
report on the SMPTE - Hollywood Section Meeting
March 17th, St. Patrick's Day, a lot of people in the TV and film
world showed up at Gene Autrie's Western Heritage Museum. The meeting
itself was a panel discussion on "The Digital Transition -
Report from the Trenches. Among the speakers were Bill Bouroghs,
Engineering, KCET, Ed Gordon, Director of
Engineering, E! Entertainment Television, George Hamilton, Manager,
NBC High Definition Studios, James A. Smith, Director of Engineering,
KMEX and Dan Sullivan, Manager of CBS Video Tape Technical Operations.
Horace Scott, VP of Engineering Operations, KCET was the moderator.
Prior to the meeting in the Mary Pickford
Auditorium there was a demonstration of HDTV DTV. Panasonic supplied
two DTV ready receivers, one a m/n CT 32XF55 480p only 30"
DTV ready set and a 35" m/n DTM 3050 HDTV DTV ready set.
Both were fed from a Panasonic DTV Receiver. Sony supplied one of
their Wega Flat Screen 34" HDTV's and a DTV receiver to
it. In addition the HDTV signals were displayed on a computer monitor
model CDM W900 in a 16 x 9 format. The signal was received off the
air on an ordinary Radio Shack Antenna and split with a Winegard
four way splitter.
lot of people were impressed with the fact that the HDTV being broadcast
in 16x9 format was also being shown simultaneously on the 4x3 480p
only Panasonic DTV set.
would have transmitted some HDTV at 720p but they had some technical
difficulties and were off the air at the time of the demo that was
between 6:oo p.m. and 8:00 p.m. PST.
was transmitting a locally produced HDTV travel log program on the
sights and sounds in and around Los Angeles, CA, narrated by the
local anchor person Anne Martin. The equipment used a Panasonic
HD D-5 for playback with it's signal fed to a Utah Scientific HDTV
switcher then to a Mitsubishi HDTV MPEG-2 encoder and uplinked to
Mt. Wilson using a
Twinstream Digital STL. From the digital receiver to the Harris
transmitter and then to a Dialectric CP antenna.
was transmitting upconverted regular programming from its regular
NTSC feed. A Snell & Wilcox MDD2000 "Golden Gate"
Decoder up converting to 1080i with a Snell & Wilcox HD5050
Up-Converter and encoding with a Tiernan THE1 Encoder at 19.4 Mbs
the signal was linked to Mt. Wilson by a California Microwave "Twinstream"
Digital STL and fed to a Comark "Advantage" Xmtr with
a Dielectric CP antenna.
used the Sony HDCAM playback of the "Rose Parade" using
NDS encoding equipment and uplinked to the Comark IOT DTV transmitter
using a STL by Microwave Associates.
Horace Scott's opening statement he said "What you saw next
door was nowhere near as good as its going to be when display devices
are developed out to the 1920 x 1080 spec. and the beam sizes reduced
to light a single pixel. These pictures will be much, much better
than what we are looking at today."
Scott thanked Steve Bloom, KCBS and Frank Geraty, KTLA for the broadcasting
of HDTV material during the SMPTE demonstration.
was interesting listening from all the panel members. One of the
panel members, James A. Smith, KMEX, said management wants KMEX-DT
to go digital with HDTV and be the #1 TV station in the LA area.
He elaborated on the problems up on Mt. Wilson and with the US Forrest
who want to clear up some of the clutter up there. KMEX-DT will
erect a candelabra on Mt. Wilson and share it with other broadcasters.
Other members of the panel had interesting "war stories"
on their experiences with DTV.
The DTV Tech Notes are published for broadcast
professionals who are interested in DTV, HDTV, etc., by Larry Bloomfield
and Jim Mendrala. We can be reached by either e-mail or land lines
(408) 778-3412, (805) 294-1049 or fax at (805) 294-0705. News
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