Washington Apple Pi

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Preparing for The Switch to Digital TV Broadcasting

By Dick Rucker

Washington Apple Pi Journal, reprint information

By now, everyone knows that ALL “full-power” analog TV (ATV) broadcasting “over the air (OTA)” will cease by February 17, 2009, to be replaced by digital TV (DTV) broadcasting. If you are still relying on an ATV set, you will need to do one of the following:

A fourth, but not usually recommended, option is a DTV set or set-top box that is CableCARD™ capable – consult Google for references.

A case in point:

In 2003, my wife and I bought a Sony Wega TV set and upgraded our Cox cable service to High Definition TV (HDTV), swapping our old “set-top” box for a new “HD Digital Receiver (HDDR).” This allowed us to enjoy DTV programming in our family room, but in our kitchen, an old ATV set with a “rabbit ears” antenna remained.

Back then, Cox offered 4 HDTV channels; Cox now offers 41, along with 180 Standard Definition (SDTV) and other channels, most viewable only for extra fees. Some channels are available at no additional cost and don’t require the set-top box to watch them.

So we had a decision to make: Our ATV was too old to keep and since we had Cox service, our question was: Which new DTV set do we purchase and do we rent another HDDR?

We bought a new  Samsung DTV set and did not rent another HDDR. We also bought a two-way signal splitter, which divides the incoming signal power between two outputs. Our Cox cable is connected to the splitter’s input; one output is goes to the HDDR and Sony DTV; the other goes to our Samsung DTV in the kitchen.

Fortunately for us, the signal strengths presented to both sets remained sufficient, but other folks have had to add a signal amplifier to one or more of the runs from their n-way signal splitters. Still others have found that adding an amplifier has interfered with their cable-supplied Internet service.

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, but an attempt to help you understand what the transition to DTV is all about and to become aware of of a few potential problems.

Over-the-Air (OTA) Broadcast TV Transmission in the US

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:
channels 2 thru 4 ( 54 to 72 MHz)
channels 5 thru 6 ( 76 to 88 MHz)
channels 7 thru 13 (174 to 216 MHz)
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)

What benefits are expected to accrue from the move to OTA DTV?

Since digital broadcasting uses the radio spectrum 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, possible reasons for preferring the new digital standard include:

(1) seeing program images in much higher resolution, with truer, 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) being able to participate in interactive programs.

The latter depends in part on packet-data protocols from the Internet.

A down side is that DTV signals are either “on” on “off” so they are either detectable or they are not. In the past, when a signal has been weak, you might have watched the program anyway. With your new DTV set, if the signal is weak, you will not see the program at all. This is known as the “cliff effect.”

What do these technical terms mean?

NTSC refers to a standard adopted by the National Television System Committee (NTSC) in 1941 to support the transmission of monochrome pictures: images are transmitted as a series of 525 horizontal lines that, at the receiving end, are scanned onto a display at 60 lines per second. Scanning occurs in two interlaced passes: odd-numbered lines in one pass and even-numbered lines in a second, resulting in a refresh rate for the picture of 30 times per second. Successive images are displayed within a frame whose width-to-height, or aspect ratio, is 4:3.

 In 1953, NTSC added “chroma” information so that pictures in color could be transmitted. All color TV sets sold in the U.S. until recently followed this standard.

Traditionally, when the display 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.

Modulation & bandwidth in NTSC: A TV channel is 6.0 MHz wide and contains three modulated carriers: two for the video’s “luma” and “chroma” information, and one for the audio’s sound information. Video is Vestigial Side Band (VSB) modulated onto its carriers; audio is Frequency-Modulated (FM) onto its carrier.

In VSB, 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:


ATSC refers to a family of digital signal transmission standards adopted by the Advanced Television Systems Committee (ATSC) – for details see http://en.wikipedia.org/wiki/ATSC_Standards.

ATSC formats: Many are defined, including:
Standard definition (SDTV): 480i to maintain compatibility with NTSC.
Enhanced definition (EDTV): 480p to match the quality of movie DVDs.
High definition (HDTV): 720p for compact transmission of HD images and 1080p for sharp resolution on all screen sizes; i = interlaced (2 pass scanning) and p = progressive (1 pass scanning).

The goal is for all DTV broadcasters to use the 1080p format, but the standard allows for HD broadcasting at 720p or 1080i in the interim. Most DTV receivers are being built to scan at 1080p and to convert to that 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: The 6 MHz bandwidth remains, but all signals are now digitized and compressed before the carriers are modulated. Because of gains in efficiency, the bandwidth required is now one-fourth that previously required. Consequently, either a more- demanding HDTV program, or up to 4 SDTV programs, can be transmitted within one channel. 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 use 8VSB modulation, a more capable version of VSB, with a maximum data rate of 20 megabits per second (Mbps).

The Role of the Cable TV and Satellite TV operators

Cable TV operators; e.g., Cox, Comcast, and Verizon, and satellite TV operators; e.g., DirectTV, rebroadcast programs to their subscribers for monthly fees. The FCC has a “must-carry” rule requiring them to carry either the analog or digital transmissions – but not both – of terrestrial broadcasters when so requested.

Cable TV operators use more benign transmission media than wireless broadcasters; i.e., coaxial cables and optical fibers. Consequently, cable operators are able to use either 16VSB or 256-QAM modulation, methods that achieve data rates about twice that of 8VSB modulation.

Their internal methods of transmission are expected to remain unchanged, so their set-top boxes must convert the signals being received into formats acceptable to either your ATV or DTV set, as well as unscrambling any premium channels.  A similar observation applies to Satellite TV operators.

Cox Communications in Northern Virginia uses a mixed network of optical fibers and coaxial cables to transmit signals from its head–end plant in Merrifield, Virginia, to its customers. For a photo-tour of Cox’s head-end plant, see:


 “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

The DTV-to-ATV Converter Box

This is a box inserted between your TV antenna and your ATV set to convert the ATSC signals received OTA into the NTSC format. The federal government will send you up to two coupons worth $40 each. Each can be applied to the purchase of one converter box. For details and coupons: https://www.dtv2009.gov/

Installation instructions for converter boxes can be found here:


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.

What can you expect from wireless reception of DTV signals?

Consider reception of DTV signals relayed by a satellite stationary above the Earth’s equator. DirectTV subscribers in the Washington DC area must have unobstructed views to the southwest in order to “see” its satellite. Once the antenna is installed and aimed, you’re done.

During installation, a customer’s antenna is adjusted in azimuth and elevation until the strength of the received signal from the satellite 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.

DTV signals to be received from a terrestrial broadcaster’s antenna are more problematic. The further away the transmitting antenna is,  the more the Earth’s curvature works against reception. There is a range beyond which reception is no longer possible. TV broadcasters typically assume that all consumers have antennas 30 feet up. Because of the “cliff effect,” consumers on the fringes will discover that DTV is not nearly as forgiving as ATV.

Website http://www.antennaweb.org/ lists antennas that can receive broadcasts within some range of your location, plus a map showing azimuths to the stations within range. The latter is important if you are considering a directional high-gain antenna.

The ranges and directions to all TV broadcast antennas, ATV and DTV, within range of a specified location can also be looked up here: http://www.2150.com/broadcast/default.asp

Viewers living in a building of many dwelling units are often dependent upon an central antenna, signal-splitters, and long feed lines, components that may well be past their prime. Reception problems can be expected.

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.

Reports from some folks who have experience with using OTA DTV

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 monthly 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.

How far along is the build-out of DTV broadcasting in the US?

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.”

Some things to be aware of:

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:


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.”


I wish you success in finding a solution in your situation.