Portable TVs
- A Brief History
Introduction
High definition television, the 405-line version of its day, was first introduced in 1936. In the intervening 70 years or so the television set has become perhaps the most influential invention of the 20th century. Early portable TVs however, were "portable" in name only, in the modern sense of the word; the presence of a CRT or "Cathode Ray Tube", meant that they were deep and heavy by necessity. Not only that but early portables were not terribly robust, suffered from poor picture and sound quality, and more often than not, required mains power, further restricting their already limited portability. Thankfully, much has changed since those early pioneering days; recent advances in audio-visual and battery technology, flat panel LCD ("Liquid Crystal Display") or Plasma television screens, and Li-Ion ("Lithium Ion") and Li-Po ("Lithium Polymer") battery technologies for example, mean that modern portable TVs are truly portable and have lots of features.
History of the Portable TV
The first real portable TV, although still incredibly heavy by modern standards, was a vacuum tube or valve model produced by Ekcovision in 1955. The Ekcovision TMB272, as it was known, was capable of operating on mains power or batteries, and was used extensively by the BBC as an outside broadcast monitor.
The next link in the evolutionary chain, as far as portable TV is concerned, was the introduction of transistorised TV sets in the late 1950s. A transistorised model was demonstrated in the laboratory, by RCA ("Radio Corporation of America") as early as 1956, but the first production model was the Philco Safari, introduced in 1959. The Philco Safari measured 15" x 8" x 5˝", large enough for a portable TV, and featured a vertically mounted 2" picture tube, from which pictures were reflected through 45° by a mirror, to produce a viewable image. The Philco Safari was followed closely by the TV8-301 from Sony, which featured 23 transistors and 19 diodes, and was an offshoot of research and development into radio technology.
By 1971 Sony was manufacturing the TV-100 portable TV, which was capable of operating on 12-volt or 240-volt power supplies and featured an 11", 90°, CRT and a UHF ("Ultra High Frequency", the frequency band between 300MHz and 3000MHz) tuner. The Sony TV-100 weighed in at just 15˝lbs.
However, at around that time, the first LCD displays based on the TN ("Twisted Nematic") field effect of liquid crystals were produced. The TN field effect was patented by Hoffmann-LaRoche in Switzerland in 1970, and subsequently licensed to the Japanese electronics industry. The TN field effect allows the behaviour of liquid crystals to be controlled precisely at low operating voltages, and was therefore used as the basis of alphanumeric displays in digital watches and pocket calculators etc. Furthermore, in contrast to the inferior DSM ("Dynamic Scattering Mode") type of LCD panel devised during the early days of development, TN field effect LCD panels are capable of fast response times, and can be produced in very thin form factors. These characteristics were to revolutionise the development of the portable TV and indeed, of the TV in general, in the years to come.
The first "active matrix" a.k.a. TFT or "Thin Film Transistor" LCD panel was produced by T. Peter Brody, in the United States in 1972. Thin film transistors, as the name suggests, are tiny switching transistors and capacitors, arranged to form a matrix on the glass substrate of an LCD panel. The technology allows the voltage supplied to liquid crystals to be increased or decreased, in very small increments, such that up to 256 levels of brightness per pixel are possible. Active matrix LCD panels therefore solved the problems traditionally associated with older, "passive matrix" technology, namely slow response time (leading to "ghosting" of images, particularly during fast-moving action or sports footage), imprecise voltage control (leading to blurred, fuzzy images, lacking in contrast) and poor viewing angle. LCD panels are also economical to produce in smaller sizes; more economical than Plasma for example, although Plasma TVs were not introduced commercially until 1992, and therefore ideal for modern portable TVs. In fact, some major retailers including DSG International, which owns Currys and Dixons have withdrawn CRT TVs, including CRT portable TVs, from its product range such that only flat screen, high definition, LCD and Plasma TVs are available.
The arrival of DTT ("Digital Television Terrestrial") the "Freeview", free-to-air service, for example, was launched in the United Kingdom in 2002 initially presented some new challenges for portable TV manufacturers. Roughly 33% of older, analogue portable TVs operate via a set-top aerial, but there was some resistance to developing equivalent products for the digital market, by manufacturers, mainly due to uncertainty regarding coverage and the saleability of such products. However, with Freeview already available to 75% and upwards of households in the United Kingdom, and the digital TV switchover, set for completion in 2012, already under way, digital portable TV equipment has taken centre stage with manufacturers. A DTT aerial is of course, a critical component and research into new techniques (active antennae, fractal aerial designs, digital signal receivers, etc.) has had a major impact on the portable TV market. Indeed, so-called "diversity reception" techniques nowadays have significantly enhanced the quality of DTT reception in a typical living room, and even in a moving vehicle.
Current Portable TV Models
Nowadays, a typical portable TV for domestic use, as opposed to a handheld model which can have a screen measuring as little as 2 ˝", diagonally, has a screen size of 14", or slightly larger (a screen measuring 17" diagonally, for example, actually provides 20% more viewing area than a 14" screen). Many models include the capability for high quality, "Nicam", digital stereo sound previously only available on full blown TV sets, and a range of features that turn them into portable multimedia entertainment systems, rather than simply portable TVs.
Single, or twin, TV tuners (analogue and digital), may be included together with a DVD player or recorder, or a VCR ("Video Cassette Recorder"). This means that not only can you watch the 5 standard terrestrial television channels and 30, or more Freeview channels, plus of course, listen to all the digital radio stations available via Freeview; but you can record from the channel you are watching, or record one channel while watching another. Support for EPG ("Electronic Programming Guide"), PDC ("Programme Delivery Control") and VideoPlus is included, so that you choose what you want to watch and/or record easily, and actually record it even if the broadcast programming schedule changes, in a single step.
Many modern portable TVs are highly versatile with regard to media, and may support DVD in its various different flavours, DVD+/-RW, DVD+/-R, in single and dual layer versions, including MP3, MPEG4, DivX, and standard audio CD media. This means of course, that you can watch commercial DVD and downloaded content, and listen to music, or audio books, in addition to watching digital or analogue television broadcasting. Some portable TVs even include built in games.
Connectivity is also a major feature of modern portable TVs. Typically ? and in ascending order, with regard to video quality ? a portable TV is likely to feature RF ("Radio Frequency"), composite video,
S-video, SCART, and VGA ("Video Graphics Array") connections. RF connections are usually used for plugging in a portable TV to a standard aerial socket, or set-top aerial. Composite video (a.k.a. A/V if combined with audio jacks), S-Video and SCART, on the other hand, are used for plugging in VCRs, DVD players, games consoles, and cable or satellite boxes. If you want your portable TV to double as a monitor for your PC, or laptop, from time to time, a VGA connector may be required, although RCA, or BNC, connections may also be a possibility (adaptors are available between all three connection types).
Power to a portable TV can be supplied by a 240-volt AC mains supply, 12-volt or 24-volt DC supply from a car or other vehicle battery (a car adaptor is often included), standard, alkaline batteries (usually "AA", "AAA", or "D" type), or a rechargeable lithium battery. The cost of standard alkaline batteries, however, can quickly become prohibitive, particularly for larger screen portable TVs, which may require 6, or 9 ? and one or more of the other options may prove more economical in the long term. So-called "universal" rechargeable batteries are also available, typically offering a choice of DC jacks for connection to a variety of portable TV models, a choice of voltage outputs, and up to 6 hours of portable TV viewing on a single charge. These universal batteries, themselves, can be charged via mains power, or once again, via a car adaptor.
Check out our
portable TV
section
|
