Digital Boxes for cable TV
A cable converter box or television converter box is an electronic tuning device that transposes/converts any of the available channels from a cable television service to an analog RF signal on a single channel, usually VHF channel 3 or 4, or to a different output for digital televisions such as HDMI. The device allows a television set that is not “cable ready” to receive cable channels. While later televisions were "cable ready" with a standard converter built-in, the existence of premium television (aka pay per view) and the advent of digital cable have continued the need for various forms of these devices for cable television reception. While not an explicit part of signal conversion, many cable converter boxes include forms of descrambling to manage carrier-controlled access restriction to various channels.
Cable-ready televisions and other cable-aware A/V devices such as video recorders can similarly convert cable channels to a regular television set, but these do not include advanced capabilities such as descrambling or digital downconversion.
Technological description[edit]
The basic converter box is passive and does not communicate back to the carrier. It simply tunes to one of the channels being transmitted together over the wire and re-transmits it to a television or other video device on a standard broadcast frequency (usually a customer-selected, locally unused frequency between VHF 2 and 4). Like other set-top boxes, converter boxes usually provide multiple options for the output channel (either 2/3 or 3/4) so that the same box can be used, with simple configuration, in multiple television markets. Despite not having a broadcast reception television antenna, a strong local television station can cause interference with the TV's reception of the cable converter's signal, resulting in undesired static or ghosting.
Later cable boxes became addressable, allowing the carrier to independently identify one cable box from another. In early systems, this permitted the carrier to send instructions to the boxes by addressing them over the wire. This allowed customers to subscribe to premium television and pay-per-view. More recent cable boxes, particularly those for digital cable, engage in two-way communication with the carrier central office, allowing for more advanced and interactive features.
Typically, a cable converter box has two coaxial F-type female connectors; one "Cable In" for a coaxial cable from the wall jack (containing the CATV signal), one "TV Out" connected to the television where an antenna or other RF device (such as a VCR) would be connected. Newer cable boxes also tend to come standard with an IEEE 1394 interface (aka "FireWire") and RCA jacks for composite video and stereo audio. More advanced analog video devices may have S-video and/or HDMI outputs to support HDTV.
In early days, before televisions came standard with 75Ω coaxial antenna connectors, cable boxes came with adapters that would allow the coaxial cable to connect to the 300Ω twin lead screws used with traditional antennas.
Major manufacturers of cable boxes have included Jerrold Electronics, General Instrument (which Jerrold merged into), Cisco (which Scientific Atlanta merged into), and Motorola (which General Instruments merged into).
Addressable cable box[edit]
An addressable cable box is one that can be controlled by the local cable company. Addressability is the process by which (optionally encrypted) messages are sent from the cable provider for a particular cable box via the cable signal. The cable company can "address" a particular customer's cable box to command it to activate or deactivate the descrambling of selected premium or pay-per view channels. The system can also send messages. This function affords the cable company the ability to add or delete descrambling on the channels that come in through the coaxial cable line. It also allows them to remotely disable the box, for reasons such as non-payment of the cable bill or theft of the unit itself. Such commands are referred to as bullets and are a transmitted message which affects the cable box program effectively disabling or "killing" it. "Bullets" do not affect the electronics inside converters or descramblers, only the programming. Non-addressable boxes are "bulletproof", as they are unable to detect such messages.