| 摘要 |
Coded signal detection particularly applicable to telephone calling codes where the user may wish to restrict the number of people having access to the dialling code number. The detector oprates on a two wire system, and uses low power consumption, phase coupled loops connected to a relay which is normally in the unexcited or closed state. The detector compares source and local frequencies providing a beat frequency which is in turn compared with a threshold value. A filter and a compression circuit process the result to determine whether the call is to be accepted. |
