| 摘要 |
<p>767,568. Unattended repeaters. POSTMASTER GENERAL. Oct. 6, 1954 [Aug. 21, 1953], No. 23154/53. Class 40 (4). In a communication system comprising terminal stations and intermediate repeaters, the output power at which overloading of a repeater occurs is reduced by the reception at a repeater of a test current appropriate to that repeater and different in frequency from test currents for the other repeaters, and means are provided for measuring the response when a test current is applied. A two-wire system, Fig. 2, in which one band of frequencies is used for transmission from A-B and a higher band is used for the reverse direction has an oscillator O for producing test currents, and the frequencies of the currents are chosen so that a predetermined harmonic resulting from the overloading lies within the band for transmission from B-A. The returned harmonics are measured on a meter M. The amplitude of the currents of fundamental frequency may alternatively be measured at B. Facilities may be provided additionally at station B for causing the repeaters to overload at an individual frequency in the high-frequency band and a further test current which is not one of the frequencies at which a repeater will overload may be transmitted to produce combination frequencies lying within the low-frequency band by intermodulation. The reduction of output power at which overloading occurs may be obtained by connecting a crystal X, Fig. 1, across the output of the repeater. At resonance the voltage from anode to cathode is rectified in a rectifier D and applied to the grid. The rectifier may be poled to drive the working point in either direction. An alternative arrangement in a feed-back amplifier is described with reference to Fig. 3 (not shown), and arrangements suitable for a transistor amplifier are described with reference to Fig. 4 (not shown). Reference has been directed by the Comptroller to Specification 656,188.</p> |
