Analog passthrough is a feature found on some
digital-to-analog television converter boxes. Boxes without analog passthrough only allow digital TV (
ATSC standard) to be viewed on older, analog-only (
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
standard) TVs. Those with analog passthrough allow both digital and analog television to be viewed on older TVs.
Before digital television, passthrough originally existed in
VCR
A videocassette recorder (VCR) or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other source on a removable, magnetic tape videocassette, and can play back the recording. ...
s (and later
PVRs and
DVDRs) that connected to TV set using RF connector, allowing the
TV antenna
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, ...
or
cable TV signal to be switched to pass through the VCR, or have VCR output added as an extra channel.
The problem
All digital-to-analog converter boxes have both an antenna input (which accepts the
coaxial cable that formerly went directly to the TV) and an
RF output (which now goes directly to the TV). They may also have additional outputs. Any converter box converts the digital signal for the current digital sub-channel to an analog signal (at the reduced screen resolution of the analog standard), outputs that signal onto analog channel 3 or 4 (set by the user to avoid any conflict with local over-the-air channels) and sends that signal to the analog tuner in the TV. With a box that lacks analog passthrough, no other signals are sent to the output, so all analog stations are lost.
In the US, this primarily affects low-power and
broadcast translator
A broadcast relay station, also known as a satellite station, relay transmitter, broadcast translator (U.S.), re-broadcaster (Canada), repeater (two-way radio) or complementary station (Mexico), is a broadcast transmitter which repeats (or tran ...
stations, as these are exempt from the
FCC mandate to
switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
to
digital broadcasting
Digital broadcasting is the practice of using digital signals rather than analogue signals for broadcasting over radio frequency bands. Digital television broadcasting (especially satellite television) is widespread. Digital audio broadcasting i ...
in 2009, as well as foreign signals that will remain in analog form. A small number of TV receivers were also manufactured with built-in
broadcast radio
Radio broadcasting is transmission of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based radio ...
receivers; these included some small portable devices or (more rarely) sets marketed for hotel/motel use. If used with DTV converter boxes, these will need analog passthrough in order not to block incoming
FM radio signals.
The solution
Some
converter boxes offer analog passthrough, meaning that the same output
cable
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
which carries the converted
digital signal (on analog channel 3 or 4) while the converter is operating also retains all remaining
analog signals
An analog signal or analogue signal (see spelling differences) is any continuous signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the instantaneous signal voltage varies ...
upon turning the converter box off.
While this typically works to some extent with the converter box on, there is often significant signal strength reduction and/or interference on the original analog channels.
Analog passthrough signals are passed only to the
coax output, not to any other outputs provided by the unit. While other converter outputs may still be connected and used for digital TV reception, the coaxial RF output must remain connected to pass analog TV signals.
For some VCRs and TVs, this arrangement may cause a problem if the receiver uses the presence of active
composite video or
S-video
S-Video (also known as separate video, Y/C, and erroneously Super-Video ) is an analog video signal format that carries standard-definition video, typically at 525 lines or 625 lines. It encodes video luma and chrominance on two separate chan ...
connections to indicate that the signal should be accepted from those sources only. In such a case the two options would be to use the coax output exclusively, either when viewing analog TV only (which requires plugging and unplugging cables) or full-time (with the reduced digital TV quality produced using the coax output).
The majority of TVs have a button on the unit and/or remote labeled something like "TV/VIDEO", "INPUT" or "AUX", which manually switches between coax and other sources. This eliminates problems when using both sets of connections simultaneously.
United States implementation
In the US, conversion to digital TV from analog was complete by June 12, 2009.
Unfortunately, only one of the initially available converter boxes included this feature, and a year before the original transition date of February 17, 2009,
Community Broadcasters Association The Community Broadcasters Association (CBA) was a trade organization representing low-power broadcasting interests, including LPTV and Class A television stations, in the United States of America. It ceased operations in 2009.
History
Key issues ...
president Ron Bruno said four of 32 NTIA-certified boxes had the feature.
In late March 2008, the CBA filed a
lawsuit in the
U.S. Court of Appeals for the District of Columbia
The United States Court of Appeals for the District of Columbia Circuit (in case citations, D.C. Cir.) is one of the thirteen United States Courts of Appeals. It has the smallest geographical jurisdiction of any of the U.S. federal appellate co ...
, seeking an
injunction to halt the sale and distribution of DTV
converter box
A digital television adapter (DTA), commonly known as a converter box or decoder box, is a television tuner that receives a digital television (DTV) transmission, and converts the digital signal into an analog signal that can be received and disp ...
es, charging that their failure to include analog tuners or analog passthrough violates the
All-Channel Receiver Act
The All-Channel Receiver Act of 1962 (ACRA) (), commonly known as the All-Channels Act, was passed by the United States Congress in 1961, to allow the Federal Communications Commission to require that all television set manufacturers must include ...
. CBA maintained that the lack of analog support would seriously harm the
LPTV
Low-power broadcasting is broadcasting by a broadcast station at a low transmitter power output to a smaller service area than "full power" stations within the same region. It is often distinguished from "micropower broadcasting" (more commonly ...
and
class A television
The class A television service is a system for regulating some low-power television (LPTV) stations in the United States. Class A stations are denoted by the broadcast callsign suffix "-CA" (analog) or "-CD" (digital), although very many analog - ...
stations the group represents, as it is cost-prohibitive for many or most of them to convert to digital transmissions, and the new boxes would prevent viewers from being able to watch (or even being aware of the existence of) their analog-only stations.
Responding to CBA's actions, the
FCC
The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdictio ...
and NTIA urged manufacturers to include the feature voluntarily in all converter boxes, and manufacturers responded by releasing a new generation of models with the feature. Some new
DVD recorder
A DVD recorder is an optical disc recorder that uses optical disc recording technologies to digitally record analog or digital signals onto blank writable DVD media. Such devices are available as either installable drives for computers o ...
s and
personal video recorder
A digital video recorder (DVR) is an electronic device that records video in a digital format to a disk drive, USB flash drive, SD memory card, SSD or other local or networked mass storage device. The term includes set-top boxes with direct to d ...
s also provide both analog and digital tuners, and therefore could perform the basic functions of a set-top box in both modes.
In early May 2008, the D.C. district court denied the CBA petition without comment,
effectively telling the association that it had not exhausted all its efforts, and that there was not enough merit to take the case to the courts. The CBA responded by concentrating its lobbying efforts on the FCC, and by urging more funding for low power and Class A broadcasters to transition to digital, asking Congress to increase the number of such stations eligible for funds.
See also
*
All-Channel Receiver Act
The All-Channel Receiver Act of 1962 (ACRA) (), commonly known as the All-Channels Act, was passed by the United States Congress in 1961, to allow the Federal Communications Commission to require that all television set manufacturers must include ...
*
Composite video and
S-video
S-Video (also known as separate video, Y/C, and erroneously Super-Video ) is an analog video signal format that carries standard-definition video, typically at 525 lines or 625 lines. It encodes video luma and chrominance on two separate chan ...
*
Set-top box
A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of sign ...
and
coupon-eligible converter box
A coupon-eligible converter box (CECB) was a digital television adapter that met eligibility specifications for subsidy "coupons" from the United States government. The subsidy program was enacted to provide terrestrial television viewers with ...
References
{{DEFAULTSORT:Analog Passthrough
Analog circuits
Film and video technology
Television technology