A linjesender (English: "line transmitter") was a low power longwave transmitter system used for broadcasting in Norway. It consisted of a power line communication system, which fed the radio programme on a frequency in the longwave broadcasting range into domestic powerlines.
The last linjesender in Norway was closed in 1987 although the Swiss counterpart survived another ten years.
The typical powers used by linjesenders were between 250 watts and 2 kW. Most systems used frequencies in the longwave band or in between the LW and MW band although some used medium wave or frequencies below the standard LW band which required special receivers.
Wired broadcasting had several advantages over conventional broadcasting:
- Less susceptible to interference
- Potentially greater number of programmes (as overcrowding on the frequency bands was less of a problem)
- Potentially greater audio quality as wired transmissions were not subject to the same restrictions on bandwidth as terrestrial AM broadcasts.
- In a mountainous country like Switzerland it was difficult to obtain satisfactory national coverage with conventional transmitters. Particularly in the 1930s when transmissions were typically less powerful than today.
On the other hand there were practical and economic difficulties in extending such services to remote or thinly populated regions. Wired broadcasting could also be used by governments as a tool of censorship through promoting ownership of wire-only receivers which couldn't receive foreign stations.
Similar systems were used in Germany, where it was called "Drahtfunk" ("wire radio") and in Switzerland, where it was called "Telefonrundspruch" ("telephone broadcast"), both of these systems used domestic telephone lines. In some countries occupied by Germany during the Second World War these systems entirely replaced conventional broadcasting. In the Netherlands all standard receivers were confiscated and replaced with wire-only sets.
In the 1930s some towns in Great Britain used wire broadcasting experimentally either over dedicated cables (sometimes as baseband audio) or through power lines. However as the coverage of conventional broadcast stations improved the popularity of these "radio relay" or "rediffusion" systems waned and local councils were often hostile to their installation.