| 摘要 |
1,072,776. Automatic exchange equipment. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. Aug. 14, 1964 [Aug. 16, 1963], No. 33224/64. Heading H4K. Subscribers' keysenders transmit in two-outof-six audio frequency code by means of three generators each of which can send one or other of two 'possible tones, one generator being suppressed while the other two transmit, the receiving equipment comprising three receivers each of which discriminates between two tones of adjacent frequency. One of the receivers shown in Fig. 1 selects the tone pair by way of a band-pass filter L1, L2, C1 to C3 and discriminates between them in a resonant circuit L3, C4, tuned to the mean of the two tones. The output of a rectifier G1 or G2 switches transistor Ts2 or Ts3 to control bipolar outputs m and n which indicate which of the two tones is being received and which is not. The six tones are chosen to lie within an octave to reduce harmonic interference. An amplitude limiter is placed in the common input to the three receivers to compensate for the attenuation differences of subscriber's lines. To guard against the mixed frequencies introduced by the limiter the switching transistors Ts2 and Ts3 are provided with integrating capacitors C11 and C12. To avoid spurious responses the bipolar outputs of the receivers may be sampled only after they are fully switched. |
