Video sender

A video sender (also known as a DigiSender, wireless video sender, AV sender or audio-video sender) is a device for transmitting domestic audio and video signals wirelessly from one location to another. It is most commonly used for sending the output of a source device, such as a satellite TV decoder, to a television in another part of a property and provides an alternative to cable installations.

A wide range of video sender technologies exist including analogue wireless (radio), digital wireless (spread-spectrum, Wi-Fi, ultra-wideband) and digital wired (power-line communication). Other, less common, technologies also exist, such as those that utilise existing ethernet networks.

Overview

Typical video sender applications include the transmission of television audio and video signals from a lounge to a bedroom or from a CCTV camera to a display, as well as interconnecting appliances with audio, video and IP (Internet Protocol) requirements.

Most video sender systems will consist of three separate components, a transmitter, a receiver and a remote control relay (also known as a magic eye or IR blaster). The transmitter is responsible for transmitting or broadcasting a connected audio-video device, while the receiver outputs that transmitted audio-video signal to a connected television. The remote control relay permits infrared remote controls to operate the equipment whose output is being transmitted.

As connectivity standards have changed in the television and audio-video markets, so it has in the video sender market, with older models usually featuring SCART and/or composite video and newer models featuring HDMI as their key means of connection to host equipment.

Analogue Wireless

Analogue video senders have the advantage of low manufacturing costs as the audio and video signals are simply modulated onto a carrier at 2.4 GHz or 5.8 GHz. They do, however, have the adverse effect of causing reduced bandwidth to local Wi-Fi networks and, in some cases, Wi-Fi networks can cause picture interference on the video sender signal. More information can be found in the article on electromagnetic interference at 2.4 GHz. To avoid this, some video senders now use a spread-spectrum technology and can co-exist with wireless networks and share available bandwidth.

Usually there are four FM transmit channels, A, B, C & D, with stereo audio on 6.0 MHz and 6.5 MHz FM subcarriers added to the composite video baseband. These different channels can often be used to overcome the adverse effects of nearby WiFi networks.

The reverse remote control channel is usually fixed at 433.92 MHz, using whatever modulation is on the 34 kHz to 45 kHz IR remote "carrier". ASK/OOK schemes such as RC5 and RC6 work best over the RF link as the receiver uses a data slicer and AGC designed for ASK/OOK with Manchester encoding.

Analogue wireless video senders can achieve typical operating distances of up to 60 metres (clear line of sight) with DVD quality (720x576) video resolution and stereo audio.

Digital Wireless

Digital video senders are quickly becoming the most popular solution and combine the use of a system on chip (used for audio and video encoding/decoding) with a means of transmitting the signal, such as spread-spectrum, Wi-Fi and ultra-wideband.

Spread-spectrum

Spread-spectrum techniques are methods by which a signal is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference, noise and jamming, and to limit power flux density.

Some manufacturers use proprietary versions of WiFi technology, enabling typical operational ranges of up to 80 metres in-building. By also employing externally mounted antennas, operational ranges in excess 2000 metres (clear line-of-sight) have been achieved and several such models are sold under the DigiSender brand.

Wi-Fi

WiFi a standard developed by the Wi-Fi Alliance and has enabled a number of solutions for Video Sender products. Standards similar to this this technology are sometimes referred to as Spread Spectrum as they operate across a number of different wireless carriers. But other standards have created interesting additions to Video Sender products including the ability to replicate the display of a tablet computer or mobile phone using standards commonly referred to as Miracast or Airplay.

Ultra-wideband

Ultra-wideband is a technology for transmitting information spread over a large bandwidth (>500 MHz); this should, in theory and under the right circumstances, be able to share spectrum with other users.

Ultra-wideband is generally used for short-range applications (typically 10 meters or less) where a simple link is required from the source device to a monitor or television. As such it is generally unsuitable for video sender applications that would require a signal to be sent to another room.

Digital Wired

Several video sender technologies, such as power-line communication and HDBaseT, now exist that make use of existing networks, providing a wired video sender solution for distributing audio, video and internet connectivity around the home.

Power-line communication

Power-line communication (PLC) carries data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. It is also known as power-line carrier, power-line digital subscriber line (PDSL), mains communication, power-line telecommunications, or power-line networking (PLN).

HDBaseT

In 2010 a new standard for cabled applications was released called HDBaseT a consumer electronic (CE) and commercial connectivity technology for transmission of uncompressed high-definition video (HD), audio, power, home networking, Ethernet, USB, and some control signals, over a common category (Cat5e or above) cable with a standard connector (RJ45).

Legality

There are several issues which relate to the legality of Video Senders. The first is the manner in which the signal is being transmitted and the second relates to the copyright content of the material being transmitted such as DVDs and TV Programmes.

Transmitting via radio within a home

Transmitting signals wirelessly requires the product to be tested to relevant standards for wireless license exemption, these products are generally limited to 100mW and for higher power models used generally within the broadcasting industry a licence is required. If the broadcast is across LAN or via similar IP technologies such as the internet then using streaming technology does not require a license. The regulator is the Federal Communications Commission (FCC) in the United States who are responsible for the efficient use of radio bandwidth.

Copyright programme material

A subscriber may wish to distribute TV to other televisions in the home and provided a TV license is held by the homeowner there is no limit to the number of TVs that can display the same signal. How the subscriber chooses to distribute his TV signals within his home is constantly changing. With an increasing number of TV displays around the home and a need for greater definition the options continue to grow. You are permitted to distribute copyright material provided it is being viewed by the subscriber or within the subscribers property. Generally, broadcasting copyright material (which applies to just about all broadcast channels) for viewing by members of the public is illegal. There have been a number of test cases where the rebroadcast of subscription channels and off-air channels to subscribers or publicly have been declared illegal.

Enforcement

Agencies responsible for the enforcement of wireless telegraphy equipment are as follows:

UK http://stakeholders.ofcom.org.uk/enforcement/spectrum-enforcement/law

USA The Federal Communications Commission (FCC) regulates interstate and international communications by radio, television, wire, satellite and cable. www.fcc.gov/