Improving a Digital EAS With the New ATSC Signal

The subject of my previous column ("An Emergency Alert System for the Digital Era," Sept. 17, 2008) was a digital emergency alarm system for the digital 21st century in which natural disasters—not an inter-continental missile attack or (so far) even terrorism—are causing havoc on an unprecedented scale.

All DTV broadcast systems (including the first, our ATSC standard) transmit data in the form of packets of data and each packet has a header which defines the contents of the packet, much as the address on an envelope. A header for an emergency warning could be specific to all residents and businesses within each postal code in the path of the emergency. It is this addressability feature of all DTV systems that makes them capable of warning those in the threatened area while not alarming people who are not threatened.

These D-to-A downconverters and some others can be operated from vehicular batteries. The unit on the left can be plugged into the 12 volt outlet in a car, while the other would need to drop from 12 volts to 5 volts. Control of which ZIP codes should be warned is not a task for broadcasters, but of governmental agencies at local levels. Transmitting the alarm over the DTV channels would be the responsibility of broadcasters.


What a DTV signal can do that an analog signal such as NTSC could not do is to awaken sleeping persons believed by the local authorities to be threatened. Sixty years ago, that was done by air raid sirens, and these are still found along the Oregon coast and in the Hawaiian Islands because of tsunamis, which can generate devastating tidal waves that travel at about 500 mph. Evacuation or seeking higher ground are the only survival strategies for this natural disaster.

The DTV receivers and downconverters now deployed, and those in the commercial pipelines, cannot automatically turn themselves on and provide visual and audible warnings, but the next generation could, and at a very modest incremental cost, as this emergency alarm feature would be software- managed. New software would store the ZIP code of the address in which the device has been installed. The owner would use the key pad of its remote control to input his 5-digit ZIP code when prompted.

An audible alarm could be generated in software and fed into the audio amplifier just after the volume control of second generation DTV receivers so that the alarm would be sounded even if the receiver volume control was turned down or the receiver had been muted. A visual alarm could be generated in software and fed to the video amplifiers which drive the display device.

Second-generation DTV downconverters would probably be fitted with a piezoelectric audible alarm device, similar to those I've bought at RadioShack for a few dollars. The device would be enabled by software in all second generation downconverters. Likewise, a visual alarm on the front panel, probably a high intensity red LED, would flash.


Millions of people receive TV signals from translators because they live beyond the coverage area of DTV broadcast stations. In many cases these translators are owned by broadcasters, but many others are county- or community-owned. The latter translators need to advise the broadcasters whose on-air signal they translate and radiate of the ZIP codes of their audience. Translators and LPTV stations are not (currently) required to radiate only DTV signals after February 2008, but sooner or later the FCC will require such a changeover. At that time, the digital EAS as described here would be extended to viewers who receive their programming from translators.

Last month, I promised to write about mobile and portable (battery operated) DTV receivers with a digital EAS feature.

As every reader of TV Technology knows, the ATSC is working on a mobile DTV transmission signal that is backwards-compatible with existing ATSC receivers. Possibly by the end of 2008 this new standard will be finished and submitted to the FCC with broad endorsement by the broadcasters and consumer electronics manufacturers. This mobile DTV signal can be received by a new class of DTV receivers intended for mobile applications. Your next automobile or pleasure boat may have a mobile DTV receiver.

If these new mobile receivers can be upgraded by downloading additional software-driven features such as I have outlined above, everyone in the vehicles they are operated in would be warned automatically. Such receivers operate from the vehicle's storage battery, a source of limited energy. If the engine is running, its engine-driven alternator could supply the energy needed for the mobile DTV receiver, and it would be continuously monitoring one or more local DTV stations.

The mobile DTV standard being developed will overcome the limitations of the existing ATSC signal standard for mobile applications. These include a significantly lower minimum signal-to-noise power ratio than the present ATSC standard's 15.2 dB. Therefore reception of EAS warnings should take advantage of the mobile DTV signal technology, which incidentally is backwards compatible. However, only mobile DTV receivers will operate well below the 15.2 dB SNR of the present ATSC signal. This makes it essential, in my opinion, that all mobile DTV receivers have the needed software for digital EAS. Directional antennas cannot be fitted to vehicles, so the signal power from an omnidirectional antenna 2 meters above ground is going to be inherently weak, which is why the new mobile standard is being designed to work well below a 15.2 dB SNR.

An obvious question is: what is the ZIP code for an automobile? It would be the owner's residential and/or business ZIP codes. Another obvious question concerns vehicles not having mobile DTV receivers. Some first generation NTIA approved DTV downconverters are designed for 12 volt DC power (I have two of these) so I assume that second generation DTV downconverters will be available for use where a 12 volt battery is the only available power source.

DTV downconverters are very compact, so I think that they can and will be installed in vehicles once the mobile DTV standard is approved by the FCC and manufacturers battle for market share of these new products.


For mobile DTV receivers to provide a useful EAS they should have an automatic channel selection feature so that when the vehicle is away from its home town, finding no signals on its local channels (because it is outside their coverage area) it would scan all TV channels looking for locally available DTV signals. Once it has found the local DTV channels, it can monitor one of them. But it could not be addressed by its home ZIP code. So perhaps there are some unassigned ZIP codes that a receiver away from its home community could monitor for EAS. If the signal being monitored fades, the automatic channel scanning features would seek another channel with a good signal and monitor it.

This automatic channel scanning feature is also essential for home receivers too. Normally the receiver will monitor whichever local DTV station's signal was being viewed before the viewer turned the receiver off (actually to its EAS monitoring mode of operation). However, what if that station goes off the air, perhaps for maintenance or lost power or due to an equipment failure? The automatic channel monitoring feature would tune other local channels so it could continue to monitor for EAS.

These mobile DTV receivers could be upgraded to provide emergency alarms or the needed software could be embedded in them from the factory. Perhaps the FCC would mandate that all mobile DTV receivers will have this emergency alarm feature built-in. Otherwise, many people may not get their receiver upgraded or worse yet, they may believe that it already is EAS ready. We have seen a lot of misinformation about the DTV conversion and I expect that many people will get bad information about mobile DTV receivers and downconverters.

What appears in this column is my best professional opinion on the topic, and in no way should be taken as a plan under development within the industry or government. Having said this, I will add that on Oct. 13, 2006, the Congress enacted the WARN Act. The FCC established a Warning System Advisory Panel to be chaired by the chairman of the FCC, Kevin Martin.

The long, long list of members of this committee includes Kelly Williams of the NAB and representatives of several regional broadcasters including Texas, Florida and Michigan, as well as the Association of Public Television Stations and other qualified stakeholders too numerous to mention here.