During the development of PLC applications, there was a series of experiments with PLC audio services. Transmission of radio programs using amplitude modulation using long or medium-frequency bands for the local needs of larger objects (e.g. student dormitories) was dependent mainly on “clear energy networks”, i.e. on the level of interference in the used band.
Business telephone transmission was much more durable, when implemented via traction power lines. The most common applications were operating on electrical traction lines in underground coal mines, which were used for communication of work crews.
In some cases, however, such systems were experimentally implemented on railway traction lines to connect the rail dispatchers with the locomotive crew. In both cases interference (noise) was the main limitation, caused by moving trolley adapters of driving vehicles on the contact line, (i.e. sparking at the lines).
A much larger application refers to the PLC non-speech services, including remote sensing, remote control and signalling, and mentioned mass remote control. Lately, there have been applications for remote reading of power meters in households. There are also requirements for implant the transmission into the infrastructure of security systems.
Narrowband PLC technology has got its limits that have their source in communication in existing power lines. PLC is significantly influenced by attenuation, which is the function of frequency, depends on used splitters, inductance of lines, configuration of lines and distribution of load, number of taps (outlets), type of appliances bridging capabilities (e.g. for noise suppression in the appliances). Furthermore, unsatisfactory relation between the phases, if the transmitter and receiver are at different stages of distribution. Another problem for successful transmission is high level of interfering voltage that is mostly sent back to the network by the appliances themselves. This is particularly the lighting controlled by AC inverters, transformerless power supplies, electro-motors with thyristor control (drills, vacuum cleaners, mixers etc.), or even home network phones (intercoms) that operate in the same frequency bands. Furthermore, a PLC signal can be distorted because of non-linear frequency and phase or because of time-varying impedance. In order to improve broadband transmission systems, one can use an appropriate modulation, echo canceller, suppression of noise etc., Nowadays, the implementation of narrowband data transmission in a typical distribution grid to the distance of about hundreds meters up to about 5 km, is considered.
Currently, there are more applications that utilize narrowband PLC channels in an LV network for local purposes. These are mainly remote data collection systems that collect signals from various distributed media meters (electrical energy, water, gas, hot water, cold, etc.). These systems provide accurate and reliable information without the need to visit the measurement point. This reduces human error reading and labour costs. Other media distributors can profit from it, as well.