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专利名称：Apparatus for the determination of
attenuation in waveguides including meansfor comparing the amplitudes of pulsereflections
发明人：CRAVEN GEORGE FREDERICK,KARBOWIAK
ANTONI EMIL
申请号：US209362申请日：19620716公开号：US3244978A公开日：19660405
摘要：975,600. Measuring attenuation-frequency characteristics. STANDARDTELEPHONES & CABLES Ltd. July 9,1962 [Sept. 7, 1961], No. 32202/61. Heading G1U. Anapparatus for the determination of attenuation in a wave-guide at different frequenciesincludes a means for applying a series of signal pulses of continuously increasingfrequency to the waveguide, a means for automatically comparing the amplitudes ofsuccessive pulse reflections at each signal frequency and a means for recording therelative amplitudes of succeeding pulse reflections. A signal from a backward waveoscillator (BWO Fig. 1) is modulated to provide both a signal frequency source and thelocal oscillator frequency for an I. F. amplifier. These two frequencies are passed via ahybrid T network to a transducer which applies the signal frequency to the waveguideunder test through an inductive diaphragm which ensures loose coupling to the guide.The diaphragm reflects the local oscillator frequency back to the mixer, while the powerfrom the signal frequency, which has been applied to and extracted from the waveguide
through the diaphragm, passes along the same path. The reflections are blocked fromreturning to the BWO by an isolator stage, and pass through the mixer, I.F. amplifier anddetector to a comparator network, where two successive pulses are selected and theratio between their amplitudes is determined. This ratio is recorded by a pen recorder.The backward wave oscillator is modulated by applying to its frequency sensitiveelectrode a line voltage, which as it is raised increases the oscillator frequency, thisfrequency being the local oscillator frequency. Short rectangular pulses of a radiofrequency voltage are superimposed on the line voltage, so as to alter the oscillatorfrequency for the duration of each pulse to provide the signal frequency. Thediffererence between the local oscillator and signal frequencies must be maintainedconstant so that the correct I.F. is maintained for subsequent amplification, and thus theamplitude of the modulating voltage must be controlled through a circuit connectedindirectly to the line voltage supply. Such a circuit may be as indicated in Fig. 2, the pulsemodulating voltage being applied to the B.W.O. cathode across a resistor R4 from theanode of valve V 3 . The grid of V 3 is normally biased well below cut off, except when themodulation input is applied, but this bias is changed in accordance with the line voltagefrom a power supply which generates between 70'and 200 volts in accordance with anA.C. output through a transformer from the line voltage circuit. The line voltage itselfvaries between 700 and 8000V and is applied negatively to the other end of R4. Becauseof the non-linearity between the BWO frequency and the applied voltage, it must bearranged that the ratio between the modulating pulse amplitude and the line voltageincreases as the BWO frequency increases, and this is brought about by the inclusion ofthe pentode V 1 in the biasing circuit of V 3 . Part of the bias of V 1 is derived from itsanode circuit so that the bias applied to V 3 is not linearly related to the line voltage.Withthe further aid of the diode V 2 the desired relation may be achieved. The attenuation ofthe waveguide at different frequencies is determined by comparing the relative
amplitudes of succeeding signal pulses in the received train. This may be done by the useof a commercial ratiometer designed to accept signals at 1000 c/s within an amplitude
range 0. 3- 10 mV, if the signals from the waveguide are converted so as to be suitable foruse with such a ratiometer. The pulse signals are therefore fed to two identical gatingcircuits (see Fig. 4), which select successive pulses in the two channels. These pulses arestretched to give approximately level D.C. voltages, which are applied to the grids ofidentical variable Á valve stages in series with the output of a 1 kc/s oscillator. Thus theamplitudes of the 1 kc/s outputs from the stages, which are applied to the ratiometer,are functions of the pulse amplitude inputs. An alternative method of coupling theapparatus to the waveguides is described (Fig. 5 not shown) which utilizes a fastmicrowave switch operated by the modulating pulse to direct the signal frequency andthe local oscillator frequency along their appropriate paths.
申请人：INTERNATIONAL STANDARD ELECTRIC CORPORATION
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