US2373562A - Frequency modulation receiver - Google Patents

Description

Apn1-1o,1945. C w H'ANsELL 2373.562

FREQUENCY MoDULATIoN REQEIVE?.

angina Filed June 17, 1941 Potented Apr. 1 0, 1945 'FUNITEPPSTAI'E sA PATENT OFFICE aereas? renommer Monm'noNnEcmvEn Clarencew, HanselLlort Jefferson, N. Y., assignor-to Radio Corporation o! America, a corporation of Delaware A'application June 17, 1941, serial No.

398,391. Divided and this application September 22, 1942, Serial No. 459.273

' 5 Claims. (C1. Z50-20) 'I'his application is a division of my application` Serial No. 398,391, med June 17, 1941, Patent No.

2,323,596, dated July 6, 1943. This invention relates to new and improved methods of,` and means for, reception or frequency modulated carrier current. In its-. boader'aspects it involves new and improved-methods offand means for, carryingout 2B and condenser 22 to the anode 24 of tube It, -The third' grid 2 5-oi tube AII is-'coupled by-se1' les A connected resistance 26 and condenser 28 to the' anode 30 of tube I'. Thesecouplings Provide' regeneration to produce an unstable condition so that' over the operating frequency range, one tube the fundamental principles-of frequency'modulai -tion (F. ML): receptionwhich were described in my United States Patent' No. 1,813,922. In the said patent I described meansior providing constunt energy, or constantelectrical change, per cycle of an intermediate frequency (I. F.) carrier current in a superheterodyne frequency modulation receiver, followed by means for integrating and utiiizingthe successive energies, or currents, to provide an output current, or increment of. output current, proportional to the'frequency-of the intermediate frequency current. That is, I provided means for producing equaljenergy, or our? ing 4I) of a transformer 42. The secondary winding 44 of the transformer is connected between the rent, pulses at a rate determined b'y the frequency of an intermediate frequency carrier current, and utilized these pulses to produce a'flow of power1 or of current, which varied in proportionto frequency variations of the carrier current.

The novel features which I believe to be characteristic of my invention are set -forth with particularity in the appended claims; theinvention itself, however, as to both its. organizat=on and method or operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically severfal circuit organizations whereby my invention may be carried J into effect. Y

In describing my invention reference 'will be made to theattached drawing whereinl Figs. I and 2 each show a modification of a fre-Y quency modulated wave energy demodulator ar; ranged in accordance withmy invention.

In the arrangement oi'Fig. l-receivedradio signals (FM signal energylare-supplied from antenna A to circuits in unit VIl comprising radio frequency ampliiiers. a source oi lofai oscillations,

a ilrst detector and I, F. ampliiier`s. {i'h' radio signals are heterodyned down in unit 2to an intermediate frequency, ampliiiedf'and'applied by the transition. Therefore, the wave form of curanodes 46- and 48 of a double diode 5B, The ltubes I4 and I 6 are, coupled by the transformer 42 to the rectier 50 which, in turn, supplies audio frequency current through a low pass filter 52 to an audio amplier 54 and loudspeaker 56. In operation, the intermediatefrequency current controls the frequency rate at which the two tubes, Vwith their circuits, throw the current balance from one tube to the other, but the rel generative feedback determines the quickness of rent pulses, and themagnitude of electrical charge Der pulse delivered" to the rectifier Sli,l are Y substantially independent of the pulse frequency rate. Consequently, the mean direct lcurrent.

vpassed through the rectiiier 58 and low pass iilterv 52 to the' load 5 4 and 5B is substantially propor- .tional to the pulserate, provided the load imi pedance is not too'high in comparison with the effective impedance of the source of current for the load. '40

' With this combination, whenafrequency mod;

' ulated radio carrier is being received, there is a.

way oi' resistances 'E and B to respective 'grids III and I2 orga pan-1 or eigenen discharge tubes. la and Ii which are provided with regeneration sumcient to producev a condition of unstable equilibrium. The regeneration may-be obtained in various ways.

corresponding modulation of the intermediate frequency and of the pulse rate. Hence, the rectied curreniiafter going through the low pass lter 52, varies in magnitudesubstantially in proportion to the frequency, andhas variationst corresponding to the modulation of received' cur'- rents.; In the arrangement of Fig. 1,- "-I have "shown tubes I4 and I6 each having three grids placed successively in the electron streambetween.

cathode and anode. In eachtube one'l grid '(grid III in tube'l4 and grid I2 in tubel I6) receives the Y intermediate frequency control potential, another 1 In a preferred embodiment'the'ilrst gridIB of tube :Il is Vcoupled by series-connected resistance acts as a screen (grid-II!" in tube I4 and grld- I2' 5.5' -in tube I6) between tube input and output circuits, and the third (grid I8 of tube Il and grid 25 of tube I6) is utilized for feedback potentials to provide the desired instability of current balance between the two tubes. The two tubes and their circuits are closely related to the tripping circuit invented by my associate, J. L. Finch, as, for example, disclosed in United States Patent No. 1,844,950, dated February 16, 1932, which has found wide application in vcommunications systems. Since, Vas pointed out above, the magnitude of the electrical charge per pulse delivered to the rectifier 50 is substantially independent of the pulse frequency rate, the arrangement of Fig. 1 automatically performs the functions of an amplitude limiter and frequency modulation detector, and differs from the circuit of the aforesaid Finch patent in this important respect; The circuit of Fig. 1 performs the functions with simpler and lower cost equipment, which produces less distortion when correctly proportioned. Y

The system of Fig. l'may be modified as illustrated in Fig. 2. In Fig. 2 the antenna A feeds the FM signals to the heterodyne detector and intermediate frequency amplifying means 3. In the latterthere is reduced the frequency of the received modulated wave, while increasing the percentage modulation thereof. Network 3 feeds the I. F. energy to transformer 5, and, thence, by way of resistances and 8 to the control grids I8 and 25 of tubes I4 and I6 which in this modiconnection with Fig. 1, alternately pass current.

The duration of the impulses depends on the constants of the tube circuits, and is substantially independent of the amplitude of the input. The frequency of reversal (twice per cycle of applied intermediate frequency current) depends on the frequency of the input. The alternating current output is fed to transformer 42, and rectified as in Fig. 1. f

I have illustrated my novel frequency modular' tion detector circuits as applied to radio receivers, butit should be apparent that they are also applicable to any kind of frequency modulation communication or telemetering system, including f electrical communication over wire circuits, through wave guides, and signalling by vibrational waves through gases, solids or liquids, such as submarine signalling. They may be used advantageously in receiving sun-carrier frequency assez systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention'is by Vno means limited to theparticular organizations shown and described, but that many modications may be made without departing from thescope of my invention, as set forth in the appended claims.

What I claim is: v

l. In means for demodulating frequency modulated wave energy, a pair of electron discharge tubes each having at least an anode, a cath- ,ode and a control electrode, circuits cross-connecting the anodes and-control electrodes of said tubesv to thereby connectl the same in a regenerative circuit whereby pulses of current of constant amplitude are generated, means for impressing frequency modulated. wave energy in push-pull relation on the control electrodes of said tubes whereby the rate of said pulse generation is controlled in accordance with the wave energy frequency,'a rectifier coupled to the anodes of said tubes for rectifying said pulses, and a low pass lter coupled to said rectifier to pass the modulation components of the rectied pulses.

2. In means for demodulating modulated wave energy, a pair of,electron discharge tubes, each including an anode, a cathode and a plurality of control electrodes, means cross-connecting each anode and a rst control electrode of the opposite tube thereby providing cross-regeneration between the tubes, means for impressing negative potentials on said control electrodes relative to said cathodes, means for impressing modulated `wave energy in phase opposition on second con-Y trol electrodes of said tubes, whereby impulses of current are produced on the anodes, and a rectifier coupled to the anode electrodes to rectify said current impulses. Y

3. In a receiver of angular velocity-modulated carried wave energy, an amplitude limiter stage comprising a pair of tubes having a common wave energy input circuit, each tube including at least a cathode, anode and control electrode, a common output circuit connected to the anodes of said -ltubes, aregenerative feedback path connected between the anode of each tube and an electron control element of the 'opposite tube whereby there are produced pulses of current of a, controllable rate. and of substantially constant amplitude, means for connectingsaid control electrodes to said common input circuit in push-pull relation whereby the rate of pulse production is modulated signals in multiplex systems, and in lfacsimile communications systems such, for example, as disclosed in C. W. Hansell Patent No.

1,819,508, dated August 18, 1931; C. W. Hansell .Patent No. 2,025,190, dated December 24, 1935.

The invention, and the detailarrangements shown, provide for substantial suppression of amplitude modulations, or amplitude limiting, 'as well as for demodulation'of frequency vmodulated waves with simpler and less expensive equipment than heretofore used. Y

. While I have indicatedand described several controlled in accordance with the frequency of received modulated wave ener-gm, and means coupled to said common output circuit for utilizing the controlled pulses.

4. In a receiver of angular velocity-modulated carried wave energy, an amplitude limiter stage comprising a. pair-'of tubes having a common wave energy input circuit, each tube including at least a cathode, anode and control electrode, a common output circuit connected to the anodes of said tubes, a. regenerative feedback path connected between' the anode of each tube and an electron control element of the opposite tube whereby there v,are produced pulses of current of a con;

trollable rate and of substantially constant amreceived modulated wave energy, and means coupled to said common output circuit for utilizing the controlled pulses and said electron control elements consisting of auxiliary control electrodes provided in said two tubes.

5. In a reeciver of angular velocity-modulated carried wave energy, an amplitude limiter'stage comprising a. pair of tubes having a common wave energy input cincuit, each tube including at least a. cathode, anode and control electrode, a com- Y mon output circuit connected to the anodes of said tubes, a, regenerative' feedback path connected between the anode of each tube andan electron control element of the opposite tube whereby there are produced pulses of current of v utilizing means.

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