Cable television represented a possible alternative to deployment of UHF converters as broadcasts could be frequency-shifted to VHF channels at the cable head-end instead of the final viewing location. Unfortunately, cable brought a new problem; most cable systems could not accommodate the full 54-890 MHz VHF/UHF frequency range and the twelve channels of VHF space were quickly exhausted on most systems. Adding any additional channels therefore needed to be done by inserting the extra signals into cable systems on non-standard frequencies, typically either below VHF channel 7 (midband) or directly above VHF channel 13 (superband).
These frequencies corresponded to non-television services (such as two-way radio) over-the-air and were therefore not on standard TV receivers. Before cable-ready TV sets became common in the late 1980s, a set-top box known as a cable converter box was needed to receive the additional analog cable TV channels and convert them to frequencies that could be seen on a regular TV. These boxes often provided a wired or wireless remote control which could be used to shift one selected channel to a low-VHF frequency (most often channels 3 or 2) for viewing. Block conversion of the entire affected frequency band onto UHF, while less common, was used by some models to provide full VCR compatibility and the ability to drive multiple TV sets, albeit with a somewhat non-standard channel numbering scheme.
Newer television receivers greatly reduced the need for external set-top boxes, although cable converter boxes continue to be used to descramble premium cable channels and to receive digital cable channels, along with using interactive services like video on demand, pay per view, and home shopping through television. Satellite and microwave-based services also require specific external receiver hardware, so the use of set-top boxes of various formats never completely disappeared.
In the United Kingdom, digital set-top boxes (often referred to as digiboxes, after Sky Digital's trademark for their unit) are usually for digital terrestrial television through services such as Freeview, a service operated by the Freeview Consortium, or through digital satellite with BSkyB and also with digital cable. They are used to access television as well as audio and interactive services through the "Red Button" promoted by broadcasters such as the BBC with BBCi or Sky with Sky Active. Current Freeview set-top boxes and digital televisions are not capable of decoding the protocol DVB-T2 that terrestrial High-definition will use in 2009, so viewers will need to purchase an HD receiver when the time comes.
In Australia set-top boxes are the principal means of receiving digital terrestrial broadcasts as comparably few television sets have in-built digital tuners. The Foxtel set-top boxes (including the Foxtel iQ unit) are also used to receive subscription television from Foxtel. For HDTV receiving they are using Beyonwiz manufactured media centers which came to market at March 2007.
In the United States, deployment of a very basic coupon-eligible converter box is supported through a $40 federal subsidy to encourage viewers of over-the-air television to adopt ATSC standards ahead of the shutdown of full-power analog broadcasts planned for February 17, 2009. These boxes are not readily available in Canada and Mexico, where broadcasters are not yet required to transition to digital television, although ATSC-capable tuners are appearing in some new TV's and television-related products such as computer video capture cards, satellite receivers and DVD recorders.
Most of the set top boxes in France are distributed by the Internet providers and allow the consumer to have access to IPTV, VoIP, Internet and media centre functionalities.
A set-top box does not necessarily contain a tuner of its own. A box connected to a television (or VCR) set's SCART connector is fed with the baseband television signal from the set's tuner, and can ask the television to display the returned processed signal instead.
This SCART feature had been used for connection to analogue decoding equipment by Pay TV operators in Europe, and in the past was used for connection to teletext equipment before the decoders became built-in. The outgoing signal could be of the same nature as the incoming signal, or RGB component video, or even an "insert" over the original signal, thanks to the "fast switching" feature of SCART.
In case of analogue pay-TV, this approach avoided the need for a second remote control. The use of digital television signals in more modern pay-TV schemes requires that decoding take place before the digital-to-analogue conversion step, rendering the video outputs of an analogue SCART connector no longer suitable for interconnection to decryption hardware. Standards such as DVB's Common Interface and ATSC's CableCARD therefore use a PCMCIA-like card inserted as part of the digital signal path as their alternative to a tuner-equipped set-top box.
The distinction between external tuner or demodulator boxes (traditionally considered to be "set-top boxes") and storage devices (such as VCR, DVD or disc-based PVR units) is also blurred by the increasing deployment of satellite and cable tuner boxes with hard discs, network or USB interfaces built-in.
However, users of computer-based solutions such as Linux MCE and MythTV have a very flexible list of possible features ranging from basic DVR-like functionality to features such as DVD copying, home automation, and house-wide music/video file playing. They also can fix any software bugs just by joining the development team.