7. The magnitude of the balanced component is indicated by how much the lines corresponding to Af=+75 kc. I have, therefore, found that in practice it is desirable to reproduce the family of curves as shown in Fig. In a typical case they totaled 25 mmf. and A/f=-75 kc. Either point 30 on resistor 27 or point 31 may be grounded, and the audio signal output taken off at point 32 at the junction of condensers 25 and 26. No resistance (direct current) between point 32 and either of points 30 or 31 is necessary. 2, then vector E" would be longer than vector E'. In combination with a source of frequency modulated carrier waves, a discriminator network for deriving from the waves a pair of carrier wave voltages whose relative magnitudes are dependent upon the frequency modulations of the waves, two rectifiers, circuit connections between said discriminator network and said rectifiers for impressing said voltages on respective ones of said rectifiers, a rectifier output circuit coupled to said rectifiers and including a stabilizing network having a time constant that is longer than the duration of a cycle of the modulation signal, thereby to stabilize the rectified output voltage with respect to variations of the amplitude of the waves, and a resistive impedance element included in said stabilizing network for reducing the portion of the rectified output voltage which is stabilized. in width to provide for reasonable tolerances, such as oscillator frequency drift and the like. It can be seen that the diodes 13 and 14 are arranged in reverse relation relative to the connection in a conventional FM detector circuit of the type employing balanced detector circuit diodes. Privacy Policy In practice, when a battery or a large condenser is used across the resistance (tapped resistor 27), any variation in the input signal automatically causes the equivalent load resistance to vary in such a way as to keep the audio output constant, provided, of course, that the detector circuit parameters are properly related. value, this calls for a time constant of the order of 0.1 second and for capacitance values of the order of a microfarad. 18) Examples of low level modulation are. The detector of Fig. The received signal is x c(t)=A c cos(ω c t+φ(t)) where φ(t)=φ Δ(t)x(t) for PM Angel modulation ; The angle of the carrier wave is varied according to the information-bearing signal ; Lesson 1 Angle modulation is a nonlinear process, which testifies to its sophisticated nature. 9. To fix this, follow with a limiter and a bandpass filter. In combination with a source of angle modulated carrier waves, means for deriving from the waves a pair of signal voltages whose relative magnitudes are dependent upon the angular modulations of the waves, at least two rectifiers, means for applying each of said pair of voltages to a respective rectifier, a single direct current path which carries substantially all the unidirectional current which flows through either rectifier, means for deriving the modulation voltage from across at least one of the rectifiers, means for stabilizing the rectified output voltage, and means in circuit with the stabilizing means for controlling the effect thereof. These various circuits and circuit components are very well known to those skilled in the art of radio communication, and 4 need only be briefly referred to. The tube immediately preceding the discriminator input network of the detector circuit may be a normal I. F. amplifier giving full output except as it may be controlled by the AVC action, as shown in Fig. It is not believed necessary to repeat the detailed analysis of the electrical relations existing in the ratio detector circuit of Fig. This tends to maintain the output potential constant for any applied frequency in the presence of amplitude modulation as shown in the curves of Fig. At the quadrature detector’s input, the FM signal takes two paths. My invention is not limited to such arrangement of the circuit portion of the closed loop on the input side of the rectifiers, as clearly appears from Fig. Ans. It is, also, usual to design the signal transmission circuits to have a pass band of approximately 200 kc. 5 is a modification of Fig. In combination, a source of frequency modulation waves, a discriminator therefor, a pair of diode rectifiers, means connecting the anode of one rectifier and cathode of the second 5o to predetermined spaced points of said discriminator, a condenser of low impedance to modulation frequency currents connecting the cathode of said one rectifier to the anode of the second rectifier, a resistor in shunt with the condenser, a second condenser of low impedance to said waves connected from a point on said discriminator to one side of said first condenser, means for deriving modulation voltage from across the second condenser, and resistive means of predetermined magnitude in a series circuit with the first condenser. ANGLE MODULATION METHODS (b) Show that for a single-tone AM, μmax is 33.3% at ma =1. 1, the circuit on the input side of the rectifiers may be said to be constituted by the coil 16 of the discriminator and the connections for impressing voltages from the discriminator on the rectifiers. In the present application it is assumed, by way of specific example, that the receiver is designed to operate over the present 88 to 108 megacycles FM band or over the former FM broadcast band of 42-50 megacycles (mc. The converter may be of any desired construction, and is preferably preceded by one or more stages of selective high frequency amplification. In general, it ]5 is desired to employ a network constructed and arranged to derive from angle modulated waves a pair of voltages whose relative amplitudes vary in accordance with the angular deviations of the waves with respect to a predetermined reference condition (whether phase or frequency). Phase and Frequency Modulation Think about what it means to modulate the phase of a cosine. Here the basic extremes are amplitude modulation, where the phase does not depart from the carrier phase, and angle modulation, where the amplitude is kept constant. It is first assumed that the FM signals applied to the primary circuit 5 are instantaneously at the mean or carrier frequency of 8.25 or 10.7 me. The junction of the condensers 40 and 41 is connected to point 30. 11. In combination with a source of angle 7 modulated carrier waves, means for deriving from the waves a pair of signal voltages whose relative magnitudes are dependent upon the angular modulations of the waves, at least two rectifiers, means for applying each of said pair of voltages to a respective rectifier, a single direct current path which carries substantially all the unidirectional current which flows through either rectifier, means for stabilizing the rectified output voltage, and means in circuit with said path Sfor controlling the desired percentage of the rectified output voltage which is stabilized. 1 is constructed in accordance with my invention disclosed and claimed in my parent application above referred to. Hence, the I. F. amplifier tube immediately preceding the detector circuit may possess normal and full gain, which is the reverse of the 7 usual operating condition for an amplitude limiter. When the modulation index is less than 1, the angle modulated systems are called low index. On the other hand if a large condenser is used the voltage across the condenser will vary in proportion to the average signal amplitude, and thus automatically adjust itself to the optimum operating level. The class comprises frequency modulation and phase modulation, and is based on altering the frequency or the phase, respectively, of a carrier signal to encode the message signal. If the amplitude of the input signal is constant then the current flowing into stabilizing 0O condenser current 24 is zero. “Frequency modulation is the form of angle modulation in which instantaneous frequency of the carrier is varied linearly with the instantaneous amplitude change of the modulating signal”. The output transformer feeding the final I. F. amplifier tube has its primary and secondary circuit each tuned to the operating I. P. value. Since, however, the detector described herewith produces output only in the presence of a variation on the ratio of the two applied signals, little or no output from such an interfering or "off-tune" signal results. In combination with a source of frequency modulated carrier waves, a discriminator network for deriving from the waves a pair of carrier wave voltages whose relative magnitudes are a function of phase deviations dependent upon said frequency modulations, at least two rectifiers, circuit connections between said discriminator network and said rectifiers for impressing said voltages on respective ones of said rectifiers, a rectifier output circuit coupled to said rectifiers and including circuit means for varying the extent of said phase deviations as an inverse function of the amplitude of said waves, and additional impedance means serially connected in said rectifier output circuit for reducing the effect of said inverse function. However, cathode 20 and anode 21 are connected to opposite ends of coil 16. 4 and 5 respectively I have shown FM ratio detectors in accordance with the present invention embodying an arrangement for controlling the desired percentage of the rectified voltage which is stabilized. The bandwidth requirement of low index systems is approximately twice of the modulating. Stabilizing the rectified voltage, therefore, results in the equivalent load resistance varying in such a way that it decreases when the input signal rises, and increases when the input signal falls. A first approximation to the behavior of the ratio detector, then, is to consider how the output is affected when the load resistance R is varied above and below its mean operating value. The I. F. amplifier network may embody one or more amplifier tubes selectively tuned to the operating I. F. value of 8.25 or 10.7 me. Figs. However, with the circuit of Fig. Now customize the name of a clipboard to store your clips. In combination, a source of frequency modulation signals, a discriminator therefor, a pair of diode rectifiers, means connecting the anode of one rectifier and cathode of the second to predetermined points of said discriminator, a stabilizing condenser of low impedance to modulation frequency currents connecting the cathode of said one rectifier to the anode of the second rectifier, a pair of series-connected condensers in shunt to said stabilizing condenser, said pair of condensers having low impedance to signal currents, said discriminator having a connection to the junction of said pair of condensers, means for deriving modulation voltage from said junction of the pair of condensers, a resistor in shunt with said pair of condensers, and means in circuit with said stabilizing condenser to control the desired percentage of the rectified voltage which is stabilized. 4, may be divided into "balanced" and "unbalanced" components as a matter of arbitrary convenience. Referring now to the accompanying drawing, wherein like reference characters in the several figures designate similar circuit elements, there is shown in Fig. While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention. Aug 25, 1977 - Sony Corporation. What do you understand by narrowband FM? If you continue browsing the site, you agree to the use of cookies on this website. Specifically, iron cores or slugs may be used for adjusting the inductance values of the respective coils S, 10 and 16, if coil 16 is so arranged that varying the 5 slug does not unbalance the two halves of the coil. The discriminator network is generally of the type shown and claimed in my U. S. Patent 2,121,103 granted June 21, 1938. It follows that if the sum of these rectified voltages is maintained constant by a suitable means and if their ratio remains constant, the individual rectified voltages will also remain constant. In a superheterodyne receiver the converter is fed with oscillations from a local oscillator whose tank circuit includes an adjustable reactance device, usually a variable condenser or adjustable inductor. For instance in an FM broadcast receiver operating with a 10.7 me. In combination with a source of angle modulated carrier waves, a discriminator network for deriving from the waves a pair of carrier wave voltages whose relative magnitudes are dependent upon the angular modulations of the waves, two rectifiers, circuit connections between said discriminator network and said rectifiers for impressing said voltages on respective ones of said rectifiers, a rectifier output circuit coupled I to said rectifiers and including a stabilizing network having a time constant that is longer than the duration of a cycle of the modulation signal, thereby to stabilize the rectified output voltage with respect to variations of the amplitude of the waves, and an impedance element coupled to said stabilizing network for modifying the stabilizing effect thereof. These curves can be graphically reproduced on an oscilloscope by applying a sine wave voltage to the horizontal deflection plates, and utilizing that sine wave for 100% amplitude modulation of a carrier signal. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. These two residual components are implicit in Figs. If point 30 is grounded, it may be desirable to use balanced audio bypass condensers 40 and 41 across the resistor 27 as shown in Fig. Then E1+E2 will, also, double. TKH 48$'5$785( '(7(&725 FLUFXLW EORFN LQFOXGHV D 3+$6( 6+,)7(5 /,0,7(5 D 3+$6( DETECTOR, and a FILTER (see the image below). In Fig. INTRODUCTION s(t) =Ac cos[θ(t)] Instantaneous frequency of angle modulated wave s(t) is given by, fi(t) =(1/2π)dθ(t)/dt In the case of an un-modulated carrier, the angle becomes θ(t) = 2πfct + fc 3 • Angle modulation is the process by which the angle (frequency or phase) of the carrier signal is changed in accordance with the message signal An angle modulation detector which prevents a demodulated output from being influenced by fluctuations in the amplitudes of signals generated from angle-modulated signal sources such as a phase-modulated signal and a frequency-modulated signal, even if the amplitude of a driving voltage applied to a connection between the bases of a pair of transistors constituting a phase detecting … In combination with a source of angle modulated carrier waves, a discriminator arrangement of reactance elements for deriving from the waves a pair of signal voltages whose relative magnitudes are dependent upon the modulations of said waves, a pair of rectifiers each having at least an anode and a cathode, connections for applying each of said pair of voltages to a respective rectifier, a circuit connecting the anode of one rectifier to the cathode of the other, a second circuit connecting the cathode of the firstmentioned rectifier to the anode of the secondmentioned rectifier, said circuits in series with said rectifiers constituting a closed loop for flow of uni-directional currents, a resistor in said second circuit, a condenser of large capacity connected across said resistor for establishing and maintaining direct current potential substantially fixed against modulation frequency variations, additional condensers connected in series across the terminals of said second circuit and in parallel with said resistor, said last-mentioned condensers being of such value as to have negligible impedance to the angle modulated carrier waves and to attenuate the high modulation frequencies more than lower modulation frequen:~5 cies, a connection from a point between said condensers and said discriminator arrangement from which modulation-frequency voltage variations may be derived, and a further resistor of a predetermined magnitude in series with said -40 large capacity condenser for controlling the stabilizing function thereof. In practice, this modulation will not be perfect, and there will be some amplitude modulation remaining. In prior detection systems which were inherently immune to such undesired AM effects the means employed was either relatively uneconomical as compared to the cost of a special amplitude limiter stage prior to the detector, or the degree of immunity to undesired AM effects was insufficient. However, there would not be O6 caused extraneous output in such a detector when supplied with the aforementioned resistors and whose characteristics are as indicated in Fig. 1, it is readily possible to determine whether the detector constants, the primary-secondary inductance ratio, the primary and secondary Q's, the coupling, the diode perveance and the operating load resistance are such as to yield good amplitude rejection. The amplitude and the phase of the carrier signal remains constant whereas the frequency of the carrier changes. Then, any impedance across one coil will appear unchanged in phase angle across the other, and the impedance appearing across both may be lumped and considered to be across only one. Define phase modulation? The coil 16 is shunted by condenser 5 18. & Terms of Use. One major distinction between different modulation types is on how a baseband message contained in the signal x(t) is impressed upon the modulated output y(t). These values are in no way restrictive. The amplitude of the carrier is maintained constant. In general, the ratio detector can reject higher percentages of upward modulation than it can downward modulation. If, now, the resistor III of Fig. 6 will be reproduced successively on the face of the tube. This action of the stabilizing voltage in varyM' ing the effective diode load resistance provides a convenient method for analyzing the mechanism of amplitude rejection. 4, 6 and 7 show a general method for controlling the desired percentage of the rectified voltage which is stabilized. The noise at the detector output is (a) the in-phase component (b) the quadrature-component (c) zero ... 14.An angle-modulation signal is given by ( )=cos(2×2×106 +2×30sin150 +2×40cos150 ) 614,956 filed September 7, 1945. If the frequency of the FM signals at circuit 5 deviated to the opposite side of center frequency, resulting in the angular position (E"s) for Es shown by the dashed lines in Fig. It is desirable to design the ratio detector so that the signal can fall to as low a value as possible without the diodes being cut off. 10. In other words, condenser 26 provides an R. F. ground connection for the discriminator network. If at some later instant the FM signals have a frequency different from the resonant frequency of circuit 12, there will occur a phase shift of the signal energy transmitted through the transformer S, 10, 16 which is greater or less than 90 degrees, depending on the direction and the extent of frequency difference between the instantaneous frequency of the FM signals and the predetermined resonant frequency of the tuned circuits 5 and 12. There are two types of angle modulation as under: (i) Phase Modulation (PM) (ii) Frequency Modulation (FM) Q.3. 6. and -75 kc., then extraneous amplitude variations would cause extraneous output in an angle modulation detector with the characteristics shown by Fig. Each of coils S, 10 and 0 16 may be of the known inductance trimmer type, or capacity tuning may be used. 2 and 3 respectively show different vector relations between the primary and secondary voltages of the discriminator input network of the detector; Figs. 2, as stated previously, I have shown the manner in which the vector voltages applied to diodes 13 and 14 will vary with modulation. In each of Figs. This can be better understood by observing the following figures. The predetection part of an angle modulation receiver is the same as for amplitude modulation. 6. My present invention relates generally to detectors of angle modulated carrier waves which are insensitive to amplitude variations, and more particularly to an improved circuit for deriving the modulation from a frequency modulated (FM), or phase modulated (PM), carrier wave without allowing co-existent amplitude modulation (AM) variations to result in substantial detector output potentials. The phase deviations of the secondary voltages with respect to the primary voltage are of course dependent upon the angular modulations or upon the frequency of the input wave. Decreased interferences from adjacent channel signals and markedly reduced side responses as the desired FM signal is tuned off resonance, are outstanding features of the present FM detector circuit. It is believed sufficient for the purposes of the present application to point out that in the present ratio type of F1M detector the problem of making the detector insensitive to amplitude variations of the received frequency-modulated signal has been met by splitting the rectified I. F. voltages into two parts in such a way that the ratio of the rectified voltages is proportional to the ratio of the applied frequency-sensitive I. F. voltages. Hence, the right hand terminal of coil 10 is at ground potential for I. F. currents, since the condenser 26 connects it to ground. 4 and 5. Square law diode modulation b. The connection or lead 61 is shown connected to anode 22 and the upper end of resistor 27, and is designated "AVC" to denote that it is an automatic gain, or volume control, lead. Angle modulation is a class of carrier modulation that is used in telecommunications transmission systems. Then the vertical plates are connected through a direct current amplifier to the modulation voltage output point 32 of the detector system and the grounded midpoint 30 of the resistance 27. The selective circuits of, and preceding, the converter may on the other hand be of the fixedly tuned type, if desired. The magnitude of the condenser 24 is chosen so that the anode 22 of diode 13 is at ground potential with respect to modulation frequencies i. e., audio frequency currents, as well as for I. F., currents. The converter may use the well-known pentagrid tube, or it may use separate oscillator and mixer tubes. It will be seen that the total secondary voltage Es has undergone an angular shift (E's) relative to the primary voltage. 7. It is to be clearly understood that the diodes may have their electrodes embodied 5 in a common tube envelope, as in the 6H6 type tube. The process of extracting an original message signal from the modulated wave is known as detection or demodulation.The circuit, which demodulates the modulated wave is known as the demodulator.The following demodulators (detectors) are used for demodulating AM wave. If you continue browsing the site, you agree to the use of cookies on this website. These resistors, I I in Fig. Some important demodulators (detectors) used for demodulating are: 4, or the resistors 112 and 113 of Fig. We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. Angle modulation 1. (a) Find μ for AM modulation index ma=0.5. 1, coil 10 is shunted by condenser 15 to provide a parallel resonant circuit tuned to the operating I. F. Coils S and 10 are wound so as to have a very high coeffient of coupling, and for simplification of the analysis the coefficient of coupling may be considered to be unity. Angle Modulation: 5 4. 3 that the phase of the secondary vectors has been rotated almost to its extreme, and that frequency modulation in this "off-tune" position of the signal causes little or no change in the relative vector potentials applied to diodes 13 and 14. If a battery is used, operation is limited to a signal at least strong enough to overcome the fixed bias created by the battery. But in Frequency Modulation (FM), the frequency of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal. 2 with respect to the primary voltages Ep, the secondary voltages, together with the primary voltage Ep, being impressed on rectifiers 13, 14. See our User Agreement and Privacy Policy. The relative magnitudes of the resultant carrier wave voltages E' and E" are a function of the phase deviations of the secondary voltages Es (or Es' or Es") in Fig.