Method and circuit arrangement for the reduction of the interference toe between a first frequency modulated signal and a second frequency modulated signal

摘要

1514556 Reducing interference between radio signals DECCA Ltd 6 Sept 1976 [24 Sept 1975] 39195/75 Heading H4L Interference between two FM signals, e.g. video and audio signals to be recorded on the same track of a disc, is reduced by amplifying the second signal at 8, and attenuating the first signal at 5 at least in the frequency region covered by the second signal, in dependence on a control signal derived by detecting the first signal in the said region. The circuit of Fig. I acts to maintain the level of the audio signal (42), Fig. 4 (not shown), 6 dB above that of the video signal (41), as the video sideband amplitude in the frequency region of the audio signal varies. This region of the video lower sideband is separated by a filter 6 and detected 7 to provide the control signal which is applied to amplitude modulator 8 and bandpass filter 5. The control may be non-linear via networks 9, 10 respectively. Bandpass filter 5 is centred on the video carrier frequency, 3À56 MHz, and produces variable attenuation of the sidebands, in response to the control voltage, by adding filtered and unfiltered components (V 2 , V 1 respectively), Fig. 2 (not shown).