US2491331A - Receiver for frequency-modulated waves - Google Patents

Description

Dec. 13, 1949 E. H. PLUMP RECEIVER FOR FREQUENCY MODULATED WAVES Filed March 20, 19 0 HE TERODYNE DE 7'- AND I. F. AMPLIFIER FREQUENCY. MODULA r/o/v DETECTOR INVENTOR MAN/V PL UMP I ERNST HER ATTO R N EY law/7kg Patented Dec. 13, 1949 ES I RECEIVER FOR CY MODULATED Ernst: H ermann "Plump, Berlin; Germany vested in-the Attorney-:Gcneralof the Unitedstates Application March 20, 1940,"Serial Nuisance In Germany February -9 1939 7 Claims. In order toprovitle a receiver-'for frequency modulated waves which' has an extremely low noise potentiaL -th'e I proposal has already been "made to render the width ofthe receiving filter narrow as compared With "the frequency stroke --ana w shift-as regards-its frequency the Working curve of the i'ilter orthe*potential,- to be demodulatei in the rhythm of the gained modulation potential such that the demodulation takes place always within the"'same working range "of thetworkingcurve. Such a receiver is of particular importance in the case-of short waves-and ultra-short Waves.

A noise potentialwhich" is practically sufiicient'ly low is obtained withe's'ubstantiallysmaller requirements as .compared'withthe said proposal, if-fi in accordancewith the present invention, in receivers for frequency-modulated Waves, more especially for short waves and ultra-short waves, the band width is varied in dependence on the gain modulation potential in such a manner that there corresponds with a small frequency stroke or swing a small band width and with a large frequency stroke or swing, a large band width. Hence, the invention originates from the teaching that only at small signal amplitudes a very low noise potential is necessary, while the latter can increase when the signal amplitudes become larger. The variation of the band width is hereby so carried out that the proportion of the frequency stroke or swing and band width remains almost constant at any frequency stroke or swing. In receivers for amplitude-modulated waves, it is known to vary the band width for the purpose of controlling the selectivity. In this case, this variation is carried out in dependence on the amplitudes of the incident waves in such a manner that when powerful transmitters are received, there is a low selectivity assigned to the receiver, and when weak transmitters are received the selectivity assigned to the receiver is high. In the receiving arrangement according to the invention however, the amplitude of the arriving waves is of no importance to the variation of the band width.

In describing my invention, reference will be made to the attached drawings wherein the single figure illustrates a frequency modulation receiver including the intermediate-frequency band with controlling means of my invention.

The band width of the receiver according to the invention may be varied for instance by varying the coupling or by a detuning of the coupling filter. The band width of a coupling filter can be controlled by means of known control elements ..2 such as if or: instance by means .of' tubes,- not conductors, rectifiers, or by varying the, preliminary --mag'netization ofanfiron coil.

:The variation of the band width :of the receiver 5 according to" the invention may. also be advanl tageously' irealizedl by varying: the damping of one'or of severalintermediatefrequency circuits. 'The' damping may herebysuitably be varied .by mea ns 0f a controllable resistance .suchas; (for instance; by mea'ns of a "damping atube; or ilrot conductor. iAneXample of construction is shown {inthe figure in :whichonlyi l those 1 details are sh'own which contributetoan understanding :of the invention. Ais: anaerial s'upplying wave en- -ergy to amplifier 2 connected: at its output ato;the

grid 4 of interme'diate frequency amplifier tube.6. The anode 8 of tube" 6 is connected with a circuit i I o -tuned to the intermediate frequency. 'r i-Ihe output of 8 is supplied to tube I6. In the figure, items 6 and [6 are intermediate-frequency amplifiers which supply frequency modulated waves to a demodulator in 20. 24 is an audio-frequency amplifier. The audio-frequency output of 20 is supplied to rectifier GI and the detected audiofrequency potential (detector GI) operates upon the grid 28 of the damping tube DR which functions as a controllable resistance and represents a variable damping of the intermediate frequency circuit.

What is claimed is:

1. In a receiver for frequency modulated signaling currents comprising a filter circuit and I control means for controlling the admittance band width of the filter circuit, the method of reducing the disturbing effects of interference which consists in applying a wide band of received signal frequencies to the filter circuit, causing the filter circuit to pass said band of frequencies and causing said control means automatically to vary the admittance band width of the filter circuit in accordance with the extent of the frequency deviations of the signal.

2. A frequency-modulated carrier-signal receiver comprising, a carrier-frequency signaltranslating channel including a band-pass selector, means for adjusting said band-pass selector to control the width of the pass band thereof, a frequency-modulation detector coupled to said channel, rectifier means responsive to the detected signal amplitude for deriving a control-bias voltage, and meansfor utilizing said control-bias Voltage to control said adjusting means to adjust the pass band of said selector directly in ac cordance with the degree of modulation f a, r ceived carrier signal.

3. A radio receiving system for frequency modulated signal currents comprising, in combination, a resonant circuit adapted to pass a band of frequency modulated currents, a vacuum tube having its plate connected to one terminal of said circuit and its cathode to the other terminal thereof, and means for automatically decreasing the plate resistance of said tube in accordance with an increase in the range of frequency variations of the received signal.

4. In a receiver for frequency modulated signaling currents comprising a selective circuit adapted to pass a wide band of signal frequencies and an electron discharge path connected across the terminals of said selective circuit, the method of reducing the disturbing effects of interference which consists in deriving a control voltage which varies in accordance with the extent of the frequency variations of the received signal and controlling the amount of the current passing through said discharge path by means of the control voltage.

5. A frequency-modulated carrier-signal receiver comprising, a carrier-frequency signaltranslating channel including a band-pass sepass a band of frequency-modulated carrier cur rents, damping means including an electron discharge tube coupled to said resonant circuit, a frequency-modulation detector coupled to said resonant circuit and a rectifier device responsive to the detected signal amplitude arranged to vary the internal resistance of said discharge tube and thereby control the damping effect of said damping means in such a manner as to adjust the pass band of said resonant circuit directly in accordance with the degree of modulation of the received carrier signal.

'7. The method of reducing the disturbing effects of interference in a circuit for relaying frequency modulated wave energy comprising a network having a band pass of variable Width which consists in impressing the frequency modulated wave energy thereon and deriving wave energy passed thereby, providing band width control by impeding said impressed Wave energy in accordance with potentials derived therefrom which vary in a manner commensurate with the frequency variations of said impressed wave energy, and controlling the said impeding effect in accordance with said potentials to thereby vary the band pass width of said network accordingly as the frequency of said wave varies.

ERNST HERMANN PLUMP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,819,508 Hansell Aug. 18, 1931 2,010,131 Beers Aug. 6, 1935

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