| 摘要 |
An attenuator control arrangement for use in a frequency multiplexed communications system includes a light-dependent attenuating resistance which is controlled in normal operation by the level of a pilot tone, in the multiplexed signal being attenuated, being used to control a light-emitting diode which illuminates the light-dependent resistance. A second light-dependent resistance also illuminated by the light-emitting diode is used to provide a control signal for the light-emitting diode in the event that the pilot tone is not detected, whereby a stable attenuation is provided in the absence of the pilot tone.
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