Digital Television Transition in The United States - Impact - Loss of Service

Loss of Service

A major concern is that the broadcast technology used for ATSC signals called 8VSB has problems receiving signals inside buildings and in urban areas, largely due to multipath reception issues which cause ghosting and fading on analog images, but can lead to intermittent signal or no reception at all on ATSC programs. DTV broadcasts exhibit a digital cliff effect, by which viewers will receive either a perfect signal or no signal at all with little or no middle ground. Digital transmissions do contain additional data bits to provide error correction for a finite number of bit errors; once signal quality degrades beyond that point, recovery of the original digital signal becomes impossible, and the image on the screen freezes, or blinks back and forth to totally blank black.

The maximum power for DTV broadcast classes is also substantially lower; one-fifth of the legal limits for the former full-power analog services. This is because there are only eight different states in which an 8VSB signal can be in at any one moment; thus, like all digital transmissions, very little signal is required at the receiver in order to decode it. Nonetheless, this limit is often too low for many stations to reach many rural areas, which was an alleged benefit in the FCC's choice of ATSC and 8VSB over worldwide-standard DVB-T and its COFDM modulation. Additionally, without the hierarchical modulation of DVB, signal loss is complete, and there is no switch to a lower resolution before this occurs.

A hundred-kW analog station on TV channels 2 to 6 would therefore be faced with the choice of either lowering its power by 80% (to the twenty kilowatt limit of low-VHF DTV) or abandoning a frequency which it occupied since the 1950s in order to transmit more power (up to 1000 kW) on the less-crowded UHF TV band. Such stations can keep the same channel number, however, because of ATSC virtual channels. Unfortunately, the higher frequencies are challenged in areas where signals must travel great distances or encounter significant terrestrial obstacles. Most stations in the low-VHF (channels 2–6) did not return to these frequencies after the transition. About 40 stations remained in the low-VHF after the transition, with the majority in smaller markets (with a few notable exceptions). The FCC has long discouraged the digital allocation on low-VHF channels for several reasons: higher ambient noise, interference with FM radio (channel 6 borders FM at 88 MHz), and larger antenna size required for these channels. After the transition, many viewers using "high-definition" antennas have reported problems receiving stations that broadcast on VHF channels. This is because some of the new antennas marketed as "HDTV antennas" from manufacturers such as Channel Master were only designed for channels 7–51 and are more compact than their channel 2–69 counterparts. These manufacturers did not anticipate widespread continued use of the long-wavelength low-VHF channels.

Stations that broadcast in analog on channel 6 have had an additional benefit of having its audio feed broadcast on 87.7 MHz, which is at the very low end of the FM radio dial. As such, many stations that use channel 6 have taken advantage of this, and directly promote this feature, especially during drive time newscasts, and as a critical conduit of information in markets where severe weather (such as hurricanes) allowed a station the advantage to broadcast their audio via FM radio without having to contract with another FM operation to do so. WDSU in New Orleans, Miami's WTVJ and WECT in Wilmington, North Carolina were among the most well-known Channel 6 broadcasters which used this approach to provide emergency information during hurricanes.

Digital television, however, does not have this feature, and after the transition, this additional method of reception is no longer available. WRGB, channel 6 in Albany, New York, used a separate transmitter on 87.7 which transmitted a polarized analog audio signal, avoiding interference with the digital TV feed and allowing the station to keep its audio on 87.7 FM after the transition to digital. WRGB ran this transmitter for approximately 6 weeks on an experimental basis, only to find that the vertically polarized 87.7 MHz signal interfered with the digital video, while broadcast of analog signals on 87.9 MHz met with FCC objections. WITI in Milwaukee took a more direct though still experimental approach to restore their TV audio, having it restored in August 2009 to an HD Radio subchannel of WMIL-FM via a content agreement with WMIL owner Clear Channel Communications. A purchase of HD Radio equipment or having a car stereo equipped with an HD Radio receiver is required to listen to this broadcast.

Planning for DTV reception assumed "a properly oriented, high-gain antenna mounted 30 feet in the air outside." The Consumer Electronics Association set up a website called AntennaWeb to identify means to provide the correct signal reception to over-the-air viewers. Another website, TVFool provides geographic mapping and signal data to allow viewers to estimate the number of channels which will be gained or lost as a result of digital transition; while it estimated that marginally more stations would be gained than lost by viewers, this varied widely with viewers of low-VHF analog signals in distant-fringe areas among the most adversely affected. An estimated 1.8 million people were expected to lose the ability to access over-the-air TV entirely as a result of the digital transition.

Viewers in rural and mountainous regions were particularly prone to lose all reception after digital transition.