By now, everyone should know that ALL “full-power” analog TV (ATV) broadcasting “over the air (OTA)” in the U.S. will cease by February 17, 2009 and that a new infrastructure of digital TV (DTV) broadcasting will take its place. If all the TV sets in your home are currently receiving TV programs from a satellite TV or cable TV operator and you are happy with the service and its price, then there’s nothing more for you to do. If, however, you are still relying on an ATV set with its own antenna, then you will need to do one of the following before the cutoff date if you wish to continue watching your favorite TV programs:
A fourth, but not usually recommended, option is a DTV set or set-top box that is CableCARD™ capable – consult Google for references.
In November 2003, my wife, Claudia, and I bought a 30” Sony Wega, a combination ATV and DTV set, and upgraded our cable service to High Definition TV (HDTV). This meant swapping our old “set-top” box for a new one: an “HD Digital Receiver (HDDR).” The upgrade has allowed us to enjoy DTV programming for almost 5 years in our family room. But in our kitchen, we had until very recently been using a 19” Toshiba ATV set with a “rabbit ears” antenna.
In November 2003, Cox offered 4 HDTV channels; Cox now offers 41. Cox now also offers about 180 Standard Definition (SDTV) digital channels plus many other On-Demand and Pay-per-View channels. Cox groups these into 15 different “service levels,” most of which must be paid for separately before your set-top box will unscramble them for viewing. Other channels are available from Cox at no additional cost and do not require using a set-top box in order to watch them.
So we had some decisions to make. The Toshiba ATV was too old to even consider buying converter box for it, and since we already have Cox cable service and one HDDR, our questions were: Which new DTV set do we purchase? And do we rent another HDDR for the kitchen?
In the end, we bought a new 19” Samsung DTV set with a 1440x900 pixel screen and decided against renting another HDDR. We also bought a signal splitter with 2 GHz bandwidth and a 50 foot length of RG6 coaxial cable. Cox cable is now connected to the splitter’s input side. One output is connected to the HDDR serving our Sony DTV; the other is connected to our Samsung DTV via the longer cable. The splitter divides the incoming signal power between the two outputs. Fortunately, the reduced signal strengths presented to both sets remained sufficient.
If signal strength had been a problem, we might have added an amplifier, but as noted on the Pi’s members-only message board “Telecomm Industry » getting ready for digital OTA TV”:
Paul Chernoff: “If you are using cable for Internet access, an amplifier will interfere with Internet packet traffic.”
Paul Schlosser: “It will. In our case we split the incoming signal, one side went to the cable modem, the other to the amplifier -- and then on to our TVs.”
Since Claudia and I depend on Verizon DSL for Internet access, this was not a consideration for us.
However, another friend wrote: “I am a Cox subscriber for both HDTV and Internet. The coax from Cox is split to feed seven outlets throughout the house. Two are connected to two HDDRs plus HDTV sets; a third is connected directly to another HDTV set. To solve low-signal problems, Cox installed amplifiers on two of the feeds. I now enjoy excellent TV and Internet performance.”
This suggests that every situation is different, so the following is not a “how-to” article. Rather, I’ll present a few key technical ideas and terms to help us understand what the transition to DTV is all about and then report on how the transition seems to be going so far for some folks.
From <http://en.wikipedia.org/wiki/HDTV_in_the_United_States>:
"On February 8, 2006, President Bush signed into law the Digital Transition and Public Safety Act of 2005, a section of the Deficit Reduction Act of 2005. This law mandated a hard shut-off date of February 17, 2009 for… all full power analog (NTSC) TV transmissions in the US… The act also provided for the auctioning off of the frequencies associated with UHF channels 52 to 69…" Since March 2007, all TV receivers offered for sale in the U.S. have been required by law to include built-in digital “ATSC” tuners to receive and decode DTV programs.
For reference, the broadcast TV channels allocated in the U.S. currently are:
At VHF:
- channels 2 thru 4 (54 to 72 MHz)
- channels 5 thru 6 (76 to 88 MHz)
- channels 7 thru 13 (174 to 216 MHz)
At UHF:
- channels 14 thru 20 (470 to 512 MHz)
- channels 21 thru 36 (512 to 608 MHz)
- (channel 37 is now reserved for radio astronomy)
- channels 38 thru 69 (614 to 806 MHz)
Since digital broadcasting uses the radio spectrum much more efficiently than analog broadcasting, some of the spectrum now used for ATV can be reclaimed after 17 Feb 09 and put to use elsewhere. Some of the spectrum to be reclaimed has been set aside for use by expanded emergency and other public services, and the rest has already been auctioned off with the proceeds going to the U.S. Treasury.
From a consumer’s perspective, the reasons for moving to the new digital standard include these possible benefits: (1) seeing program images in much higher resolution and with truer and more stable colors; (2) hearing the accompanying audio with higher-fidelity, five-channel “surround sound” (3) being able to choose the language in which the program is heard and seen; and (4) participating in programs that include viewer interaction. The latter depends in part on packet-data protocols from the Internet.
A down side of digital broadcasting is that such signals are either “on” on “off”. One consequence is that such signals are either detectable or they are not. In the past, when a broadcaster's signal has been weak into your ATV set, you might have watched the program anyway. With your new DTV set, if the signal is too weak, you will not see the program at all. This is known as the “cliff effect.”
NTSC refers to the analog signal transmission standard adopted by the National Television System Committee (NTSC) for use in the United States, Canada, Japan, Mexico… Completed in 1941 and written to support the transmission of monochrome pictures, it defined a way to transmit images as a series of 525 horizontal lines that, at the receiving end, can be scanned onto a display screen at the rate of 60 lines per second. Scanning occurs in two interlaced passes: odd-numbered lines are scanned in one pass and even-numbered lines in a second pass. This results in a refresh rate for the entire picture of 30 times per second, frequent enough to be “flicker-free”. In 1953, an update was adopted that added “chroma” information to the video signal so that pictures in color could now be transmitted. This is the standard followed by all color TV sets sold in the U.S. until recently.
Successive images are displayed within a frame whose width-to-height ratio – called its aspect ratio – is 4:3. Traditionally, when the surface being scanned was the phosphor inside a cathode ray tube, the vertical dimension was set by the width of the scanning beam times 525 lines. With the advent of modern display screens that consist of pixels – small rectangles that can be individually illuminated – a standard resolution image can be displayed on a monitor whose pixel array is at least 640 pixels by 480 pixels in size.
The standard channel bandwidth is 6.0 MHz and contains three modulated carriers: two for the video signal’s “luma” and “chroma” information, and one for the audio signal’s sound information.
Video is imposed on the carrier wave using a form of amplitude modulation called Vestigial Side Band (VSB) modulation. The higher frequency energy contained in the lower of the two sidebands – sidebands which are characteristic of true AM modulation – is partially suppressed at the transmitter. The remaining lower frequency energy, i.e., the “vestige,” is transmitted along with a much wider upper sideband. This results in several technical advantages. For the fascinating story of how VSB was invented and developed for use in TV broadcasting, go here: <http://www.ieee.org/organizations/society/bt/news/summer08.pdf>
Audio is Frequency-Modulated (FM) on a carrier at the upper end of the channel.
ATSC refers to a family of digital signal transmission standards adopted in recent years by the Advanced Television Systems Committee (ATSC) – for details see <http://en.wikipedia.org/wiki/ATSC_Standards>.
ATSC formats: Though a number of different combinations of display resolutions, frame rates, and aspect ratios, or “formats,” are defined, the following four are the most important:Standard definition (SDTV): 480i to maintain compatibility with the NTSC formatEnhanced definition (EDTV): 480p to match the picture quality of movie DVDs
High definition (HDTV): 720p for more compact transmission of HD images
1080p for sharp resolution on all screen sizes
where: i = interlaced (2 pass scanning) p = progressive (1 pass scanning)
According to a source in the local office for the ATSC, the long-range goal is for all DTV broadcasters to transmit using the 1080p format, but in the meantime, the standard allows for HD broadcasting at 720p or 1080i. Meanwhile, most modern DTV receivers are already being built to scan at 1080p and to convert to that format when the incoming signal is either 720p or 1080i.
The aspect ratio is now 16:9 to more nearly conform with that used by motion picture theaters.
Modulation and bandwidth in ATSC: ATSC retained the 6 MHz channel bandwidth, but now both the video and audio signals are digitized and compressed before modulating the transmitter’s carriers. Because of the efficiencies gained thereby, the bandwidth required to transmit an STDV program is only one-fourth that required using NTSC modulation. Consequently, either a more-bandwidth-demanding HDTV program, or up to 4 SDTV programs, can be transmitted simultaneously within one 6 MHz channel. For example, PBS broadcasts HDTV on channel 26 and broadcasts STDV on up to four virtual channels:
“26.1 26.2 26.3 26.4”
Terrestrial OTA broadcasters are required to use 8VSB modulation, a more capable version of the method used in NTSC. It has a maximum data rate of almost 20 megabits per second (Mbps).
Recall that only full-power OTA broadcasters are required to cease transmitting ATV programs. Exempted from the 17 Feb 09 cutoff are thousands of low-power stations serving communities that lie in the shadows of mountains or in rural areas not served by the full-power stations. These translator stations can continue broadcasting unaffected, according to the current law.
In a similar fashion, existing Cable TV operators, such as Cox, Comcast, and Verizon, and the various Satellite TV operators, such as DirectTV, rebroadcast programs carried by the full-power stations to their own subscribers in return for monthly fees. The FCC has a “must-carry” rule requiring these operators to carry either the analog or digital transmissions, but not both, of terrestrial broadcasters when so requested by those broadcasters.
The set-top box that you lease from your cable or satellite TV operator converts the signals being received via cable or satellite into formats acceptable to your ATV or DTV set and unscrambles any premium channels for which you have paid. Their internal methods for TV program transmission and delivery are expected to continue unchanged, at least for the time-being.
It’s worth noting that cable operators use much more benign transmission media than OTA (wireless) broadcasters. For example. Cox Communications in Northern Virginia uses a mixed network of optical fibers and coaxial cables to transmit signals from its head–end plant to its customers. Consequently, cable operators are able to use either 16VSB or 256-QAM modulation, methods that achieve data rates about twice that of 8VSB modulation.
“QAM,” pronounced ‘kwam,” is short for Quadrature Amplitude Modulation. In its most basic form, two carrier waves centered on the same frequency are independently modulated. Each is transmitted “in quadrature,” i.e., out-of-phase relative to the other. This doubles the data rate otherwise achievable. In digital systems, dependent modulation of both carriers simultaneously is advantageous because it can result in much higher data rates: multipliers of 2, 4, 8, 16… 256 can be achieved. For details, see <http://en.wikipedia.org/wiki/QAM>
“Satellite broadcasters” use other standards for re-transmitting TV programs to their customers.
This is a box inserted between your TV antenna and your ATV set to convert the ATSC signals received OTA into the NTSC format recognized by your ATV set. The quality of the picture you can expect will depend in part on the strength of the received signal. Some converter boxes have a switch that allows incoming signals to bypass ATV-to-DTV conversion and be presented to the connected ATV set, but most do not. Switchless boxes have proven to be a problem for viewers living in areas still served by both ATV and DTV “over-the-air” broadcasters.
Installation instructions for converter boxes can be found here:
<http://www.dtv.gov/wilmington/publications.html>
along with other useful information prepared for TV viewers in five counties around Wilmington, NC. These counties were selected for an early cutoff of September 8, 2008 so that all could learn how well these people coped with the transition. Some results have been posted on this website.
The federal government will send you up to two coupons worth $40 each. Each can be applied to the purchase of a converter box. For details and coupons, go here:
Let’s first briefly consider wireless reception of DTV signals as relayed by a geosynchronous satellite positioned above the Earth’s equator. For example, DirectTV subscribers in the Washington DC area must have unobstructed views to the southwest in order to receive signals from its satellite. During installation, a customer’s antenna is adjusted in azimuth and elevation until the strength of the received signal is maximized. Since a geosynchronous satellite remains in the same location in the sky, the antenna needn’t be moved again. DirectTV ads claim that reception remains reliable even during most rain storms.
There’s more to think about when considering DTV signals to be received wirelessly from terrestrial broadcasters. VHF and UHF signals broadcast from a terrestrial antenna can be thought of as circular waves spreading out over the Earth from the antenna’s location. The further these waves travel, the more pronounced the effect of the Earth’s curvature. Because of that, there is a range beyond which the transmitted signal can no longer be received by consumer’s antenna at a given height above ground. When a TV broadcaster estimates the coverage area for a planned antenna, the usual assumption made is that all consumers have outside antennas 30 feet above the ground. Because of the “cliff effect,” consumers on the fringes of coverage will discover that DTV is not nearly as forgiving as ATV.
The ranges and directions to all TV broadcast antennas, ATV and DTV, within range of a specified location can be looked up here: <http://www.2150.com/broadcast/default.asp>
Here’s a similar site: <http://www.antennaweb.org/>, a joint effort of the Consumers Electronics Association (CEA) and the National Association of Broadcasters (NAB). It provides (1) a listing of antenna types, ordered by decreasing ease of installation, that can be used to receive TV stations within range of a specified location, (2) a street map centered on the specified location with azimuth arrows aimed at the stations within range and (3) other useful links.
VHF is much more forgiving than UHF; i.e., the higher the frequency, the more difficult it is to receive signals of adequate strength at a given location, all other factors being equal.
For a report of one person’s recent experience with a DTV-to-ATV converter box, see
<http://www.spectrum.ieee.org/oct08/6814> The author is Tekla S. Perry, a staff writer for the magazine IEEE Spectrum. If her experience is representative, the transition for some may prove troublesome. She begins her article:
“I ordered two coupon cards back in January. They arrived in April, and in June I purchased a $50 RCA converter box… Like most people who watch broadcast television, I get my signals through an ancient antenna on my roof—a bent, cobwebbed, aluminum monstrosity that is… optimized for VHF signals. Most digital channels come in on the UHF band.”
The converter box worked fine, but the existing antenna system proved inadequate. Her husband replaced the VHF antenna with a new UHF antenna, but that didn’t solve all problems. A signal-splitter installed interior to a wall by a previous owner divided the received signal power among five feeds to other rooms in house. The result was an inadequate signal delivered to one set. At the time of writing the article, she was considering the purchase of an amplifier to boost the received signal.
Viewers living in a building of many dwelling units may be dependent upon an central antenna, signal-splitters, and long feed lines, and those components may well be past their prime. Reception problems can be expected in such situations.
A friend living in the City of Fairfax has a Sony ATV+DTV set connected to a 12-db gain VHF+UHF antenna on the roof of his two-story home. He reports good reception from DTV stations located to the northeast (Washington DC, Baltimore), but not-so-good reception from stations on other azimuths (he has not invested in an antenna rotor). The “SquareShooter” antenna he’s using can be found here: <http://www.winegard.com/offair/squareshooter.htm>
Another friend living in the City of Fairfax writes: “We are not fans of the mindless fare found on cable television and consequently cancelled our cable contract some years ago. But now and again we like to watch a PBS documentary or TV news program... I installed a rooftop Yagi all-band antenna that brought good analog reception on VHF, but left much to be desired on UHF.” He then added a UHF antenna and connected both to a combiner in the feed line. “I bought a Sony Bravia 40" HDTV with 1080p resolution. With this setup I get 48 HD channels… The antenna is aimed to get all of Baltimore's channels (2.1, etc); I receive the Baltimore UHF channel 45.1 clear as a bell.”
Bottom line: The adequacy of signals received OTA will depend on a number of factors including each broadcast transmitter’s effective radiated power, its range and azimuth from your location, the height and gain of your antenna, the method of feeding signals to your TV set(s), and the possible presence of buildings or terrain that either block signals or that produce multiple reflections. Because of slightly different travel times to your antenna, the latter can produce strange effects when combined at the receiving end.
Such complicating factors may drive some viewers to subscribe with their local cable TV or satellite TV operator, but, of course, there are monthlu fees to be paid for that. In the past, Claudia and I have cut back on the premium services we bought from Cox each time their rates went up. We now subscribe only to the basic tiers for SDTV and HDTV programs.
John Reiser, a friend who is a retired FCC engineer writes: “Around 700 full-power TV stations will be changing their transmitting channel as part of the transition. For a complete listing of all broadcast TV stations in the U.S. and their current status and plans for making the transition to DTV, go to <http://www.rabbitears.info>
“Many of the existing digital TV stations are now operating on temporary channels during the transition period and will be moving to another frequency sometime next year. In Washington, DC, both ABC and CBS will be moving their UHF digital operations down to their now-analog channel 7 and 9 frequencies after next February. Other stations may also have plans for later increasing power and moving or improving their antennas.
“Many DTV stations are not yet operating using their final transmitting frequencies and facilities because some digital operation of theirs had to squeeze into an existing analog allocation without causing undue interference to other analog or digital stations, and so is temporarily operating at a lower output power and with more restricted coverage. Many existing antenna towers could not support the addition of full-sized digital antennas either on top or to the side, and finding suitable locations to build new tall TV towers in major market areas has become extremely difficult.
“Broadcasters who hold allocations in the 174 to 216 MHz band have an advantage because, relative to UHF, equivalent coverage can be achieved with much lower power transmitters and much simpler antennas.”
However, as noted on rabbitears.info:
“Channels 2-6 [54 to 88 MHz] have severe problems which can be tolerated in the analog world, but cause havoc in the digital world. Chief among these is that electrical noise from lightning, as well as from… anything with an electric motor, can cause the signal to drop out or disappear completely.
“These channels also suffer from a phenomenon called ‘E-skip’ which is when ions in the E-layer of the ionosphere create a sort of mirror which reflects signals… back down to Earth. This allows stations from as far as 1500 miles away to interfere with what you are attempting to watch.”
From Paul Chernoff: “DTV refers to any program that is being delivered according to the ATSC standards, so the term encompasses both the HDTV formats of 720p and 1080i and the SDTV format of 480i. The SDTV format has the same visual resolution as the older NTSC standard and is all that an ATV set is capable of displaying. While a program you are watching may have been captured and transmitted in HDTV format, you’ll not see it in that format unless you at least have an ATSC tuner and a screen capable of displaying high-definition images.
“Keep in mind that there are different kinds of set-top boxes serving different purposes: HD digital receivers vs. DTV-to-ATV converters. For example, a DTV-to-ATV-converter has nothing to do with programs being delivered by a cable TV or satellite TV operator; it is only used to convert programs being received over-the-air from terrestrial broadcasters.
“If you have cable TV service, you will need a set-top box, or its equivalent, for each DTV set on which you want to be able to watch the premium channels; i.e., those that arrive in a scrambled format.
“You can watch unscrambled DTV programs without a set-top box so long as the TV receiver you are using can decode and display the formats of those programs.” For example, the author’s Samsung DTV set currently recognizes and displays 29 SDTV channels delivered by Cox cable in unscrambled format.”
Macintosh users have yet another option:
“If someone wants to watch Digital TV on a Mac, one can buy a 2008 model of the Eye-TV Hybrid which has ATSC. Earlier versions will convert digital over-the-air programs, but not digital programs over cable. If you have an earlier model (like I do) you will need to hook the Eye-TV up to a set-top box, and since it uses RCA jacks, HDTV programs will be converted to SDTV.” For more on the Eye-TV offering, go to:
<http://www.elgato.com/elgato/na/mainmenu/support/dtvtransition.en.html>
To help viewers quickly find available channels of interest, the Program and System Information Protocol (PSIP), one of many ATSC standards, requires all conforming receivers, including converters, to scan all DTV channels, identify those currently available for viewing, and memorize those along with their familiar labels and NTSC channel numbers; e.g., Though WRC-DT will broadcast on channel 48, the viewer will see the following in his list: “Channel 4: NBC station WRC”
The reason for this requirement as stated by John Reiser: “For years, TV stations used channel numbers for market recognition. Fox grabbed many Channel 5 outlets and identified them as ‘FOX-5’ channels, as NBC did for ‘NBC-4,’ and ABC did for ‘ABC-7.’ They were not about to give up these hard-earned marketing symbols and so fought hard to keep them.
“When first installed, each DTV receiver goes through this scanning process. After that, whenever a DTV broadcaster moves to a different channel, all affected receivers will require rescanning. While some receivers do a rescan periodically, others may not, at least not by default. Viewers who remain unaware of this need will discover that a moved station has disappeared from their set’s listing.”
That’s the story as I understand it. I wish you success in finding a solution in your situation.