Frequency detector

专利名称：Frequency detector

发明人：JAGER FRANK DE,GERWEN PETRUS

JOSEPHUS VAN

申请号：US707358申请日：19580929公开号：US2995707A公开日：19610808

摘要：844,561. Frequency discriminators. PHILIPS ELECTRICAL INDUSTRIES Ltd. Oct.10, 1958 [Oct. 14, 1957], No. 32423/58. Class 40(5). [Also in Group XXXVI] In a frequencydetector for the detection of the variation of a characteristic speech frequency situatedwithin a speech sub-band, the speech sub-band, which is selected by means of a filter 4, issupplied to two channels 6, 7 connected in parallel, the channel 6 comprising adifferentiating network 8 and a rectifier 9 and the second a rectifier 11, the outputvoltages from the channel being fed to a ratio meter 13 the output voltage of which isthe ratio of the amplitudes of the channel output voltages and a measure of the

frequency. Low-pass filters 10 and 12 are included in branches 6, 7 respectively, and, if theinput voltage of rectifier 11 is a (t) at a certain instant that to rectifier 9 is #a(t), so thatthe ratio of the output voltages of filters 10 and 12 is proportional to awdt/adt andtherefore to the frequency. In the embodiment shown, the output direct voltages offilters 10, 12 are converted into alternating voltages of frequencies fi f 2 , correspondingin amplitude to the direct voltages, by means of amplitude modulators 15, 16, carrierwave oscillators 17, 18 of frequencies f 1 f 2 and output filters 19, 20, the outputs of theoscillators and filters being connected through attenuators 21, 22 to adjust the strength

ratio of the carrierwave oscillations. A ratio meter for use in the detector is shown in Fig.4. The alternating voltage derived from channel 6 of frequency f 1 and amplitude-modulated by the rectified differentiated input signal is applied to the grid of a pentode25 through a resistor 23, the alternating voltage derived from channel 7 of frequency f 2and amplitude modulated by the rectified input signal being applied to the grid througha resistor 26. Slope control is provided for the pentode 25 and the amplitude ofoscillations at frequency f 2 at the output of pentode 25 is therefore kept constant, sothat the slope of the pentode 25 varies inversely as the amplitude of the input voltage atfrequency f 2 . The voltage at frequency fi is selected by a filter 30 and rectified, theoutput at 38, 39 being a direct voltage proportional to the amplitude ratio between theoutput voltages of channels 6 and 7. In the embodiment of Fig. 5, the ratio is determinedby amplitude limitation instead of slope control. An amplitude limiter comprisingrectifiers 45, 46 has an output consisting of a voltage of frequency f 2 modulated by thevoltage of frequency f 1 the frequency deviation of said f.m. voltage being proportionalto f 1 : f 2 , the amplitude of f 1 < amplitude of f 2 . The limiter output is fed to an

amplifier 51 and a filter 52 tuned to fi, the voltage from this filter being then rectified andgiving a direct voltage output which varies as the amplitude ratio of the input voltages offrequencies fi and f 2 . Alternatively the ratio meters may be replaced by one in which theoutput voltages of channels 6, 7 may be converted into voltages of equal frequencies,the output alternating voltage of channel 6 being subsequently shifted 90 degrees inphase and added to the alternating voltage of channel 7 so that the phase of the sumvoltage obtained varies in accordance with the desired amplitude ratio.

申请人：NORTH AMERICAN PHILIPS COMPANY, INC.

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