TV reception detecting circuit within AC mains section - has band filter arrangement with several filters tuned to uneven specified harmonics

摘要

The circuit enables to detect television receivers within a region supplied by an electric alternating voltage grid. It uses a band filter assembly, coupled to the grid which transmits a signal to a measuring instrument, this signal corresponding to the harmonics content of the mains voltage. The filter assembly (2) has several filters tuned to uneven harmonic waves above the fifth harmonic. The filter outputs are coupled to the measuring instrument (9) via a summator (4). Preferably the filters are suitable for the seventh to seventeenth harmonic of the mains voltage. Filters for the eighteenth and nineteenth harmonics may be incorporated. The assembly may contain filters for the third and fifth harmonics, disconnectable from the summator by switches (5,6). Between the summator and the measuring instrument is typically incorporated a differential amplifier (7) which receives a noise-threshold voltage (8) at its input, in addition to the summator output.