Return channel
A return channel or return path allows the telecommunications the bidirectional contact between the original transmitter , z. B. a television program provider, and a receiver .
technology
Depending on the underlying technology ( satellite , cable or terrestrial television or radio ), the effort involved in introducing a return channel differs. The classic approach, which is equally possible for all methods, consists of a supplementary medium, usually the telephone network , to which the television or the set-top box (STB) is connected via an integrated modem with an additional cable. This method use z. B. most of the devices for measuring the number of viewers, as in Germany that of the Society for Consumer Research (GfK), whose data is usually transmitted once a day at night.
In the case of cable television , the introduction of a direct route involves investments , but it is technically relatively simple. In the early days there were attempts to implement the return channel for interactive television, similar to hybrid television and home shopping . Only with the advent of the Internet via television cable at the turn of the millennium did the return channel capability spread again in the range from 30 MHz to 65 MHz.
In the case of wireless transmission, for example via satellite or terrestrial antennas, the cost of the return channel is significantly higher, since a considerable transmission power has to be applied, which means that wireless transmission is limited to ( semi- ) professional users.
Instead of the connection with the conventional telephone socket, which discourages potential customers because of the additional cable and the temporary blockage of the line, some companies are now relying on networking with mobile phones via wireless methods such as Bluetooth , e.g. B. Blucom .
- Active return channel
An active return channel amplifies the returning signal; the range from 30 MHz to 65 MHz is currently used here.
- Passive return channel
A passive return channel sends the returning signal unamplified, i. d. Usually the interference-prone range from 5 MHz to 30 MHz was used.