| 摘要 |
<p>791,277. Unattended repeaters. POSTMASTER GENERAL. Nov. 1, 1955 [Sept. 22, 1954], No. 27439/54. Class 40 (4). In an arrangement for detecting incipient amplifier faults in an unattended repeater, means are provided for selecting from the output a narrow band of a noise or distortion signal generated by the amplifier, changing it in frequency, and feeding it back to the amplifier input for further amplification. A band-pass filter E, Fig. 1, selects the noise or distortion signal and corresponding frequencies are blocked from the amplifier input by a band-stop filter D. Frequency changing is effected in a modulator F by a locally generated oscillation and the desired sideband selected by a filter J after attenuation in network H is passed after further amplification to output terminal C. For testing selectively a number of repeaters a range of spaced modulating frequencies may be used or the selected noise bands may be suitably spaced. Examples are given. The modulating frequency or frequencies may be supplied over the cable and a repeater arrangement for such a system is described with reference to Fig. 2 (not shown).</p> |
