Sometimes what seems normal just isn’t right. Consider digital-TV set-top box (STB) adapters. They accept digital broadcast television signals, and they deliver analog outputs. That’s all that some STBs being sold today do, but it’s just not enough. They need to accept analog signals, too.
That might seem strange on two counts. First, the only purpose of a digital STB adapter is to convert digital to analog for existing analog sets. Those analog sets are perfectly capable of tuning in analog signals all by themselves.
Second, the only time those digital STB adapters will be absolutely necessary is after analog television broadcasting has ceased. If there are no analog broadcasts, there should be no need to accept an analog input. But there is.
Perhaps the best way to understand February 18, 2009, the day after analog broadcasting is to cease, is to examine 2005. In 2005, according to the Consumer Electronics Association (CEA), roughly 32.5 million TV sets of all types were sold to U.S. dealers—analog and digital, direct-view and projection, flat-panel and tube based, standalone and DVD/VCR combinations. In 2004 and 2003 it was about 30 million. In 2002, it was about 32 million. In other words, give or take a couple of million, about 30 million TVs are sold to U.S. dealers each year.
As of September 30 of last year, the FCC reported there were 2,710 low-power television stations and 4,503 television translators (low-power re-transmitters) in the U.S. Also as of September of last year, the National Cable & Telecommunications Association (NCTA) reported about 73 million cable subscribers, about 28 million of them subscribing to digital cable.
Here are the last 2005 statistics to consider. As of the end of last year, according to CEA, about 90% of U.S. households had VCRs, 82% had DVD players, and about 8% had something (a TV with integrated digital-reception capability or a digital STB adapter) that could allow them to receive digital-TV broadcasts. And, in July, according to CEA, there were some 285 million TV sets in U.S. homes.
Now try fitting the pieces together. TVs with DTV tuners are being sold, but given a home TV inventory of 285 million, there will be many unequipped TVs by February 18, 2009—thus the need for those STB adapters.
If an antenna or cable feed enters the adapter, which then feeds the TV, assuming everything works as it should, viewers will be able to watch digital broadcasts. But what about those 7,213 low-power TV stations and translators, which might not make the transition to digital at the same time? What happens if a viewer has an STB (like many being sold today) that cannot receive analog TV signals nor pass them through to another device?
A viewer could disconnect the adapter and reconnect the antenna to watch analog TV broadcasts, reversing the procedure for digital transmissions. Alternatively, a splitter could divide the antenna signal between the digital adapter and an A-B switch feeding the TV. But that means lower signal levels to both tuners, with possible reception problems.
Then there’s cable. All 28 million digital cable subscribers have either cable-company STBs or digital cable-ready TVs. Some of the other 45 million cable subscribers use cable-company STBs on some of their sets. The rest rely on analog TV tuners. Someone wanting to switch between cable and digital broadcasts (the multicasts of which won’t necessarily be carried on cable) is in the same splitter-or-disconnect/reconnect quandary.
Then there are all of those viewers with VCRs and/or DVD players who are relying on channel-3/4 outputs to watch movies. A digital STB adapter with analog input or analog pass-through capability can be placed in a chain from the antenna or cable input to the STB to the TV; a digital STB without that capability breaks the chain.
Add analog reception capability to the STBs, and these situations cease to be problems.
There is one more issue. With the ascent of flat-panel TVs, the term “set-top” is dumb.
Mark Schubin is an engineering consultant with a diverse range of clients, from the Metropolitan Opera to Sesame Workshop.
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