May 09, 2008
| by Ben Hardy
Rate increases, HD-Lite, outages – there are plenty of reasons why subscribers get fed up with their HD service providers. What are the alternatives? Switch to another provider? That’s one solution, but it could simply bring its own set of problems unique to that service. There’s always Over-the-Air (OTA) HDTV. Just like your mom and dad (and grandma and grandpa) got their TV for free through the rabbit ears, so can you get your HDTV for free.
OTA HDTV in Brief
Receiving OTA HDTV is in most ways just like receiving the OTA analog signals that have been around since the days of “I Love Lucy.” Broadcast towers transmit a digital signal which is captured by the receiver (antenna), which is sent to the TV (in this case an HDTV, with either a built-in tuner or using a set-top box tuner). The antenna can be of the outdoor or indoor variety, and can include any number of accessories, including a rotor, an amplifier, and other augmenting features. The digital signals can be broadcast as VHF (Very High Frequency) or UHF (Ultra High Frequency). The VHF band covers channels 2-13, and the UHF 14-69. (After the analog to digital transition in February 2009, channels 52-69 will be claimed by the federal government for reallocation elsewhere). Stations broadcasting in digital can choose to broadcast programs in HD, and many do. Just what is broadcast in HD, and when, will vary from station to station.
One big difference between digital OTA and analog OTA is that with digital there is no in-between – you either get the channel or you don’t. As many analog OTA users will attest, “snowy” pictures can be quite common, caused by a weakened signal due to any number of factors, including distance, geography, and obstructions. The video and audio is coming through, but the picture isn’t the sharpest, though it will do. With digital, it’s an all-or-nothing situation. “We call it the ‘cliff effect,’” says Shermaze Ingram, Senior Director of Media Relations for the DTV Transition Campaign at the National Association of Broadcasters (NAB). The digital receiver (antenna) requires so many bits of data to deliver content to the television. If the signal is weak enough such that the antenna is not receiving the minimum required data, it will simply show nothing at all. According to Ingram, however, “if you are already getting good analog signal, you should be able to get good digital.”
As the controversy over HD-Lite continues to grow, many consumers point to OTA HDTV as the best source for quality, uncompressed HD. Here are some facts on OTA HDTV that the consumer needs to know. First, OTA HDTV is compressed, using MPEG-2 technology. This compression has to be done in order to comply with regulations that mandate broadcasters to use 19.4 Mbps per channel – no more, no less. However, broadcasters have some freedom to determine how much of the 19.4 Mbps is allocated for an HD program. “One can image a pie just shy of 20 Mbps around,” says Kelly Williams, Senior Director of Engineering for the NAB. “Broadcasters can divvy it up any way they want.” And most do, by multi-casting. That is, they will broadcast more than one program on a channel, creating sub-channels. As an example, in my town of Burlington, Vermont, WCAX (a CBS affiliate) broadcasts their analog signal on channel 3, and their digital content on channel 3.1. At any given time during the day they might also broadcast a different program on channel 3.2, and yet another on sub-channel 3.3. This multi-casting enables broadcasters to feed multiple programs at the same time. This can, and will, include HD content. “A broadcaster can make a nice HD picture and still have room for a couple sub-channels that require a low bit-rate,” says Williams. Where some cable companies have been criticized for sending HD-Lite content that weighs in as low as 9 Mbps to make room for all the other bit-rate-consuming content they promise to consumers, the broadcasters have a little more flexibility. The result tends to be HD content compressed only as much as is necessary to make room for a couple low bit-rate sub-channels, like a weather or radar sub-channel or an SD sub-channel that might only need 1.5 Mbps. The result is usually HD content that is in many cases superior to what subscription television service providers can offer. In fact, it isn’t uncommon to see broadcasters completely drop their sub-channels for the duration of the HD program being transmitted, maximizing the quality of that HD content.
Between watching re-runs of the The Jetsons and convincing his Insteon and Z-Wave controls to get along, Ben Hardy is immersed in the world of home automation, home control, and home networking.