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view all articles in:
The Reference Room
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Digital TV: Charles W. Rhodes
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| Poised at the Great Analog/DTV Divide |
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by Charles W. Rhodes,
9.21.2005
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Charlie Rhodes is a consultant in the field of television broadcast technologies and planning.
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While many broadcasters may wish that DTV was not about to replace analog terrestrial broadcasting, that is unrealistic. Broadcast spectrum is going to be reduced dramatically and soon. The main question now is what to do about homes that have neither CATV or DBS service. Those homes can only be reached by terrestrial broadcast signals.
MSTV and NAB are now requesting proposals for a set-top converter to allow analog receivers to continue to provide free over-the-air television service by transcoding DTV signals into NTSC signals on an RF carrier. I believe they hope to demonstrate that this is commercially feasible at a cost of around $50. As this converter offers the consumer no new service, it will have to be subsidized by taxpayers. At the $50 level, some think this may be a politically acceptable compromise. The plan is to subsidize up to 10 million such converters for households with incomes less than twice the official poverty level. The potential market for these converters is sure to attract the attention of manufacturers. If this effort by MSTV and NAB proves that $50 is possible by 2008, such a program will probably proceed and by 2009, there will be no longer any need for analog terrestrial broadcasting.
The public has not been told that the end of analog terrestrial broadcasting is only a few years away. In fact, about 20 million analog TV sets per year are being bought by consumers who haven't heard that these sets will cease to function unless they have CATV or DBS service. The problem is that for the public, there is no perceived benefit to buy a DTV receiver unless it is provides large, widescreen high-definition pictures. This is why there are so few DTV converters on the market.
Our DTV system transmits almost 20 million bits of data per second. Using only a tiny fraction of this capacity, emergency alarms could be sounded and emergency information provided to the communities served by terrestrial TV stations automatically. Automatic emergency alarm transmission systems have been around for half-a-century but until now, they all depended on a radio receiver being turned on and at a reasonable volume to receive the alarm.
With the introduction of terrestrial DTV broadcasting, the receiver can monitor incoming data for emergency alarms on a 24/7 basis. Only a small portion of the receiver needs power to do this--probably no more than an electric clock. When an alarm is broadcast locally, the receiver could emit an sound and automatically turn on the display electronics. A family so awakened would see the nature of the emergency on their TV screen and see or hear instructions on what to do. Most of that infrastructure is already in place; what is missing is the continuous monitoring and auto alarm feature.
These features could be incorporated into the taxpayer-subsidized DTV converter box that may soon be distributed nationwide. If 10 million homes were so equipped, the public would demand that retail DTV receivers offer this feature. Therefore, in less than a decade, nearly every home would have automatic emergency message alarm and monitoring, justifying the subsidization of these first 10 million converters. This is a case where the technology has arrived at exactly the time it will be most needed.
This idea of an automatic monitoring system is not new. Before World War II, RCA designed and manufactured a special Cold Cathode Relay, the 0A4-G, which could react to a burst of RF power fed through the power line to close a relay to turn on radios etc.
Today we can do much more. We can put appropriate emergency messages on the screen of every home in the local community where it is needed, and we can do it in less than a decade. Surely this justifies the subsidization of the first such receivers to be mass produced. Here is an opportunity for broadcasters to get behind a program that inherently depends on their unique position in the community.
Here is how I visualize it: The DTV converter is always on and always tuned to a local DTV channel. That said, it must be decoding the DTV datastream to downconvert the audio and video data for existing NTSC receivers, should such receivers be on. When an emergency alert packet header is received, perhaps four or five times consecutively, the converter circuitry activates audible and visual alarms.
It would not turn on the NTSC receiver; the emergency header would alert people to turn on their TV set. The emergency message would appear on-screen, and could be heard if the volume were not muted. The only cost element would be the audible and visual alarm--a large red LED on the converter. To make this work, the ATSC should assign packet headers for emergency messages. In that way, all manufacturers can incorporate software to activate the alarms when emergency headers are detected.
In a slightly more elaborate implementation, when an emergency message header is detected by the converter, software embedded in it prompts it to search for the same emergency message header on the other local channels.
If the converter finds more than one station is transmitting this emergency message header, it then sounds the alarm. In this way, a glitch in one station will not cause false alarms. The converter would use a majority vote logic routine to verify that a real emergency header is being transmitted by more than one local station, preventing broadcasters from sounding false alarms.
If broadcasters adopted this concept, I believe that receiver manufacturers would design them to automatically turn on in the event of receiving emergency headers on more than one channel. Let's see where this leads. Even those homes having a legacy DTV receiver would likely buy converters so second and third sets could receive programming after the "sunset of NTSC."
Thus, legacy receiver homes would have this public service available to them. Homes served by a CATV system would receive the emergency header and thus those homes would also receive this public service, unless the CATV system deletes such message headers--an unthinkable action.
Americans buy approximately 20 million TV receivers a year. The average life of a TV set is said to be eight years. Thus, within a decade, nearly every family could have this public service.
I hope this idea is taken seriously by broadcasters, and that they petition the ATSC to allot certain emergency data headers. Broadcasters are the only ones who can offer this vital public service. I hope my readers will take this up with station management.
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