US2048527A - Selective circuits - Google Patents

Selective circuits Download PDF

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US2048527A
US2048527A US590173A US59017332A US2048527A US 2048527 A US2048527 A US 2048527A US 590173 A US590173 A US 590173A US 59017332 A US59017332 A US 59017332A US 2048527 A US2048527 A US 2048527A
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circuit
frequency
image
coupling
band
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Harold A Wheeler
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BAE Systems Aerospace Inc
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Hazeltine Corp
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Priority to US590173A priority patent/US2048527A/en
Priority to GB208/33A priority patent/GB412942A/en
Priority to FR749563D priority patent/FR749563A/fr
Priority to DEH135012D priority patent/DE749560C/de
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
    • H03D7/18—Modifications of frequency-changers for eliminating image frequencies

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  • the present invention relates to improvements in selective electrical circuits, and more particularly to selective. circuits for preventing the reception of image frequencies" in the operation of superheterodyne radio receivers.
  • a superheterodyne type ofradio receiver has an inherent defect in that it is responsiveto signals of two frequencies each separated from the oscillator frequency by an 'amount which is equal to the intermediate frequency.
  • a receiver when such a receiver is tuned to receive a desired signal, in the presence of undesired signals differing therefrom by an amount which is twice the intermediate frequency, such undesired signals are received, converted into the intermediate frequency, and interfere with the desired signal, which has also been converted into the intermediate frequency.
  • the frequency of such interfering signals to which the superheterodyne receiver is responsive is known as the image frequency. Tuned circuits must be relied upon to suppress signals of this frequency and to prevent their being converted into the intermediate frequency.
  • a selective network for 49 selectively transferring desired signal frequency currents of any frequency in a band of frequen-- cies.
  • This network is connected between the exciting circuit, or antenna, of a receiver and a responsive device, or the receiver itself.
  • the 45 selective network comprises a broadly resonant circuit and a selective circuit.
  • the resonant circuit which may be the antenna circuit is broadly tuned to all frequencies within the band of frequencies for attenuating all signals of any 50 frequency outside of said band.
  • the selective circuit is connected between said broadly resonant circuit and said receiver, and is for suppressing all image frequency currents which are admitted by the antenna circuit and which fall 55 within said band.
  • the selective circuit comprises two signal transfer means each coupled to the broadly resonant circuit and to the receiver.
  • the first transfer means has a transfer ratio which varies greatly with frequency and has a maximum 5 transfer at the frequency of the signal, and thus selectively transfers a signal current of any frequency within a band of frequencies. However, this transfer means incidentally transfers currents of the undesired image frequency though 10 to a lesser degree.
  • the second, or auxiliary transfer means has a. transfer ratio which does not vary greatly with frequency, and thus nonselectively transfers currents of the entire band of frequencies. These two transfer means are 15 adjusted to respond equally and oppositely to signals of the image frequency.
  • the relative intensity of the image frequency currents as first and secondly transferred is so adjusted that .the currents may be balanced against each other 20 and thereby image frequency currents falling within said band be completely suppressed.
  • the first-mentioned transfer means builds up by resonance the selectively transferred currents and thus effects a much greater transfer. at the carrier frequency of the signal than the non-selective transfer of the carrier frequency by the second transfer means.
  • the second transfer means therefore has but little effect upon the transfer of the desired frequencies. Also the voltages transferred by'these two transfer means are not in opposition at the desired signal frequency, as will be explained later.
  • the amount of non-selective transference is adjusted to equal the amount of image frequency selective transference throughout the band of frequencies.
  • the circuits are so designed 'and proportioned that the frequency of complete suppression varies automatically and simultaneously with the adjustment of the selective 40 transference at the resonant frequency of the tunable circuit, and the frequency of complete suppression is maintained substantially uniformly spaced from the resonant frequency of the the resonance of the entire input circuit so that the transfer of the image frequency through the untuned circuit will be correspondingly varied.
  • this invention has particular application in connection with image frequency suppression, as discussed above, it is to be understood that it also has considerable utility in general radio reception for selectively transferring currents of a desired signal frequency and preventing interference of signals of any frequency whatever. Furthermore, the principles of this invention may be applied to each of a number of resonant circuits in one system, and thereby secure proportionately greater selectivity.
  • Fig. 1 is a schematic diagram illustrating one arrangement of the two transfer means
  • Fig. 2 is a similar diagram illustrating an alternative arrangement of the two transfer means
  • Fig. 3 is a diagram showing a curve illustrating the selective'action of the circuits of Figs. 1 and 2;
  • Fig. 4 is a diagram showing a radio antenna circuit embodying the principles illustrated in Fig. 1;
  • Fig. 5 is a diagramv showing a modification of the circuit of Fig. 4;
  • Fig. 6 is a circuit diagram showing a second modification of the circuit of Fig. 4;
  • Figs. 7 and 7A are diagrams showing a set of curves illustrating the selective action of the circuit of Fig. 6.
  • a selective coupling system comprising exciting circuit 1 including a source-0f. alternating current I0, and the two impedances Z1 and Z1, the latter of which form a path between the input terminals l2 and it.
  • a work circuit 8 exemplified by the grid-cathode circuit of the vacuum tube It.
  • the exciting circuit is coupled to the responsive device by two transfer means.
  • the first transfer means includes the circuit 9 composed of impedonce Z1, inductance L and condenser C.
  • the sec- 0nd transfer means includes impedance Zz. There is thus provided an output path including the condenser C and the impedance Z1, connected in series between the output terminals I3 and I4.
  • the first transfer means 9 is sharply resonant at or near a frequency which will be called the signal frequency. This sharp resonance is effectively maintained by making Z1 sufllciently small or by making the impedance of the source l0 sufficiently large so that the exciting circuit does not have a controlling effect upon the resonance of the first transfer means 9.
  • the impedance of the responsive device It is made sufiiciently large.
  • the current I from the source In flows through Z1, builds up a circulating current in the first transfer means 8, and thereby produces a voltage E1 across the condenser C.
  • the second transfer means Z1 is not sharply resonant at any operating frequency, and may be aperiodic.
  • the current I flowing through impedance'Zz, builds up a voltage E: across this impedance.
  • QJMQJD? v I 4 tem' iust ducribed may be reversed, retaining some of the advantages of the system as shown inFig. 1; thatistosay. llandllmay euledas input terminals and i2 and I! used as output terminals.
  • the transfer of the first means I will be denoted by the ratio 1321/1, and that of the second means, by the ratio Es/I, which latter is equal to Z1.
  • Eo/I the output voltage E0 is the vector sum of E1 and E2.
  • Fig. 2 is similar to Fig.1 except that L and C are interchanged. The effect of this change will be discussed below.
  • like parts are designated by the same reference characters.
  • the first transfer ratio E1/I is shown in Fig. 3 by the curve E1. This curve shows a sharp maximum at F1, the resonant frequency of the first transfer means 9.
  • the second transfer ratio Es/I is shown by the line E: indicating that this ratio does not have sharp resonance within the operating frequency range.
  • Interchanging L and C reverses the polarity of E: without substantially changing its value.
  • Making Z1 and Z1 of like character, in Fig. 2 brings the intersection of curves of E1 and E: below F1; while making Z1 and Z: reactances of opposite kinds, brings the intersection to a frequency higher than F1.
  • interchanging L and C hasthe same effect as changing therelationship between Z1 and Z1, and making-both changes at once has substantially no eifect UDOII-thCr'ODBlfltlOll of the coupling system. Since any frequency F1 can be suppressed in either Fig. l or Fig. 2 with the proper choice of Z1 andZm'there is no essential difference between these alternative arrangements.
  • C is a variable tuning condenser
  • the terminal ll of the condenser'C in Fig. 1. or the terminal I2 oi the condenser C in Fig. 2 may be grounded.
  • the impedances Z1 and Z2 may be of any character, such as mutual inductanees, thus producing a coupling circuit having no common terminal l3 which is at once an input terminal and an output terminal.
  • F. is the signal frequency and'Fl the image frequency, F. and Fl differing by twice the intermediate frequency. It is more common to make F1 higher than Fa, as is shown in Fig. 3.
  • the superheterodyne oscillator frequency F is midway between Fa and Ft, as indicated in Fig. 3.
  • Fig. 4 is a circuit illustrating an adaptation of the principles of Fig. 1 to a selective network or coupling system for coupling the antenna to the first tube of a superheterodyne receiver.
  • the coupling system is tuned to the signal frequency F5 and has a great selectivity against image interference, as will be explained hereinafter.
  • the antenna I6 is connected to the contact of a volume control potentiometer l8, one part of which is' shunted by condenser H, the capacity of which is equal to the capacity of the average antennna.
  • the antenna current divides in potentiometer l8, one part flowing directly to ground.
  • the other part flows through the coil l9 and fixed condenser C1.
  • the first transfer means is the closed circuit 9, which is composed, in this instance, of 01, L, C, of. which C1 corresponds to Z1 of Fig. 1.
  • the circuit 9 is sharply tuned to resonance with the signal frequency F; by varying the capacity of the variable condenser C, and is connected to the grid of the tube l5.
  • Coil iii of the circuit 1' is coupled to the coil 20 in the cathode lead of the tube I5.
  • the mutual inductance Ma between coils l9 and 20, which provides a fixed inductive coupling between the antenna circuit and the receiver, corresponds to Z; of Fig. 1 and comprises the second transfer means.
  • the condenser Cl. and the inductive coupling M2 are proportioned relative to each other so as to deliver equal and opposite voltages, at the image frequency, to the responsive device or the receiver input and thus balance out image frequency signals which are within the band through which the resonant circuit is tunable. It is to be noted that the image frequency signals which are thus balanced out are always separated from the desired frequency to which the resonant circuit is tuned by a constant frequency difference.
  • the antenna l6 and the condenser I I may have a capacity of about 200 micro-microfarads each, potentiometer i8 may have a resistance of about 10,000 ohms, coil L may have an inductance of about 260 microhenrys, condenser C may have a capacity of 350 micro-microfarads (maximum setting), and condenser C1 may have a capacity of about 3500 micro-microfarads.
  • the fixed condenser C1 has a value of the order of ten times the maximum value of the variable contual M2.
  • the circuit of Fig.4 is intended to tune to receive a signal frequency of ,from 550 to 1500 kilocycles and is intended to constant separation bears a much'greater ratio to the lower signal frequency.
  • the ratio of the impedance of C1 to the impedance of M2 is much greater at low frequencies.
  • Image transfer El/I increases proportionately to image frequency, because the decrease of impedance of C1 is more than offset by the increase of image responsiveness of the tuned circuit 9.
  • the image transfer Ez/I increases likewise, being equal to the inductive reactance of the mu-
  • the equality of the image voltages E1 and E2 is secured by selecting the correct values of the mutual M2, and phase opposition is secured by using the correct polarity of M2.
  • Z1 is the negative reactance of C1, varying inversely with frequency
  • Z2 is the negative reactance of the negative mutual inductance M2, varying'directly with frequency.
  • the ratio of Z2 to Z1 varies as a square of the image frequency.
  • the ratio of Z2 to Z1 should vary less rapidly than the square of the image frequency, but more rapidly than the first power. This is accomplished by the use of the improvements as embodied in Figs. 5 and 6, which will now be described.
  • Fig. 5 shows an improved adaptation of the principles of Fig. 1 to a system for coupling a radio antenna to the first tube of a superheterodyne receiver.
  • the circuit of Fig. 5 differs from Fig. 4 in the following respects: First, the order of E1 and E2 in series between the grid and cathode of the tube I5 is interchanged in order to permit grounding of the cathode and of the frame and moving element of the tuning condenser C. Secondly, Z1 in Fig. 1 is replaced in Fig. 5 by the mutual in- Thirdly, the antenna or primary circuit 1 of Fig.
  • Fig. 5 is broadly resonant within the tunable frequency range, resulting in greater voltage amplification from the antenna to the grid of the tube l5, and in somewhat better image suppression.
  • Z is replaced by the mutual inductance M2.
  • the antenna is connected to one side of a volume control rheostat 2
  • serves also to produce a variable attenuation and broadens the resonance of the primary circuit to include a band of frequencies.
  • the antenna current divides, one part flowing through 2
  • the first transfer means is the secondary circuit 9', which is composed of inductance L, variable condenser C and the large fixed condenser C1, and the mutual inductance M1 between coils 24 and L.
  • the secondary circuit 9 is tuned to resonance with the signal frequencyF; by variation of the capacity of condenserC.
  • the impedance Z1 of Fig. 1 is replaced by the mutual inductance M1 and the capacity of condenser C1.
  • the large fixed condenser couples the primary and secondary circuits only to a moderate degree and causes the tuning of the secondary circuit to be substantially independent of the primary circuit.
  • the impedance Z2 of Fig. 1 is replaced by the mutual inductance M1 between coils 22 and 23, which latter is connected in series with the condenser C between the grid and cathode of the tube I5.
  • the antenna 16 has a capacity of about 200 micro-microfarads, rheostat or variable resistance 2
  • the coil 24 should preferably have a very small inductance, and the mutual coupling M1 should be much less than M2, as will be explained more fully hereinafter.
  • the circuit of Fig. 5, when constructed to embody the above values, is very similar to that of Fig. 4, but is intended to work with a -kilocycle superheteroclyne amplifier. Therefore, the image frequency F1 is 350 kilocycles higher than the signal frequency F5, and has a range of from 900 to 1850 kilocycles.
  • the antenna circuit effects some improvement in image suppression by attenuating all signals outside of the frequency band over which the receiver is designed to operate, without regard to the independent means for balancing out of the voltages E1 and E2.
  • the antenna circuit including the antenna l6, coils 22 and 24, and condenser C1 in series, is resonant to a frequency near 1,000 kilocycles, which is about the middle of the tuning range.
  • has a maximum value which is great enough to permit sensible resonance in the antenna primary circuit, but which is small enough to broaden the resonance of the circuit to include all of the band, and the antenna resonance has only a negligible effect on the tuning of the coupling system as a whole.
  • the variable resistance permits varying the sensitivity of the combination.
  • the inherent selectivity of the tuned circuit 9 against the image frequency currents is much less at the higher frequencies.
  • the broad resonance of the antenna circuit offers additional selectivity against the image when F5 is in the middle or higher part of the tuning range.
  • the total inherent selectivity against the image frequency is given a higher average value and is made uniform over the entire range.
  • the signal voltage amplification from antenna to grid is also greatly improved as compared with Fig. 4, especially in the middle of the tuning range Up to this point, the effect of the grid to cathode capacitance, inherent in tube II or in the connecting wires, has been neglected. The assumption was made that the responsive device represented by tube l5 had such high impedance as not to have an important effect upon the tuning of the circuit.
  • a two-point adjustment of Fig. 5 is made possible by the condenser C1 and the mutual inductance M associated with the first transfer means 9.
  • two-point is meant that at two points in different parts of the tuning range the frequency of maximum suppression will fall exactly at the image frequency. At other points there may still be a slight difference, so that the image does not suffer the maximum suppression, but this difference is negligible when the two-point adjustment is employed.
  • condenser C1 is made as small as permissible without too greatly restricting the tuning range of the circuit 9. This value of C1 has the major effect in determining the coupling between the antenna circuit 1 and the tuned circuit 9, and therefore the degree of voltage amplification from the antenna l6 to the grid of the tube 15.
  • a representative value of C1 is ten times the maximum value of C, although lower ratios may often be employed to advantage.
  • M1 is adjusted to secure the greatest suppression of the image frequency currents.
  • the system is tuned to a frequency in the upper part of the tuning range, and the value and polarity of the mutual M1 are chosen to give the greatest suppression of the image frequency currents at this portion of the tuning range. If great precision is desired, the second and third operations may be repeated until no further improvement is possible.
  • M1 negative value of M1 is indicated in Fig. 5, which a is the correct polarity for aiding phase relation between the mutual coupling component and the capacitive coupling component, which couple 70 the square of the frequency, but more rapidly 76 aoeacar' than the first power, which is a general requisite when the image frequency remains less than double the signal frequency.
  • Two guiding rules may be stated to govern the choice of M1 in the cases under consideration, having image frequencies higher than the signal frequencies: First, a smaller frequency diiference between image and signal requires a larger negative value of the mutual M1. Secondly, a greater inherent direct capacitance across the terminals l3" and it" requires a less negative value (or even a small positive value) of the mutual M1. The second rule, in extreme cases, amounts to an alteration of the general requisites just stated.
  • Fig. 6 shows a preferred arrangement for accomplishing the same purposes as the circuits shown in Figs. 4 and 5, and for combining their respective advantages.
  • Fig. 6 has the two-point adjustment and has the broadly resonant antenna circuit of Fig. 5, but has the ungrounded tube cathode of Fig. 4 in order to minimize the direct capacitance across the terminals l3'" and H'".
  • the circuit elements of Fig. 6 are like the corresponding elements of Fig. 5.
  • M is the mutual inductance between the coils 22 and 25, which latter coil has an inductance of about 10 microhenrys.
  • Fig. 6, like Fig. 5, is intended to work with a 175-kilocycle superheterodyne amplifier so that the image frequency is 350 kilocycles higher than the signal.
  • the voltage E: across the second transfer means is nearly imperceptible on the scale of Fig. '7.
  • the right-hand slope of the curve E1 is shown in Fig. 7A on a highly magnified scale of ordinates, but with the same frequency scale. It is seen that the ratio of El/I is only about one per cent as great at the image frequency of 1,350 kilocycles as at the signal frequency of 1,000 kilocycles.
  • curve E shows the ratio of Ea/I, which is the reactance of the mutual inductance M2, having a value of 5.2 microhenrys in this particular case.
  • the curves E1 and E2 intersect at the image frequency.
  • the resultant voltage E0 is zero.
  • the curve E represents the ratio Eo/I.
  • the curves E1 and E1" represent the corresponding curves for the GOO-kilocycle signal and 1,400-ki1ocycle signal, respectively.
  • the slope ,of the curve E2 as shown in Fig. 7A, may be made so that it will intersect the curves E1 and E1".at the proper point to permit the resultant curves E0 and E0" to be zero.
  • An electrical coupling system comprising two input-terminals, two output terminals, a path between said input terminals, a path between said output terminals, a circuit tunable to a desired signal frequency, said circuit including reactances of opposite kinds, a first impedance including reactance common to both of said paths and said tuned circuit, and a second impedance common to both of said paths, the ratio of said second to said first impedance having a variation more .rapid than the variation in frequency as the frequency of the current impressed upon said circuit is varied.
  • An electrical coupling system comprising two input terminals, two output terminals, a path between said input terminals, a path between said output terminals, a circuit tunable to a desired signal frequency, said circuit including reactances of opposite kinds, a first impedance including reactance common to both of said paths and said tuned circuit, and a second impedance common to both of said paths, the ratio of said second to said first impedance having a variation more rapid than the variation in frequency as the frequency of the current impressed upon said circuit is varied and less rapid than the square of the frequency.
  • An electrical coupling system comprising two input terminals, two output terminals, a path between, said input terminals, a path between said output terminals, a circuit tunable to a desired signal frequency, said circuit including reactances of opposite kinds, a first impedance including reactance common to both of said paths and said tuned circuit, and a second impedance common to both of said paths, the ratio of the second to the first impedance having a variation as the frequency of the current impressed upon said circuit is varied which is proportional to the square of the change in frequency.
  • An electrical coupling system comprising a pair of input terminals, a pair of output terminals, a path between said input terminals, a path between said output terminals, a circuit tunable to a desired signal frequency, said circuit including reactances of opposite kinds, a first impedance including reactance common to both of said paths and to said tuned circuit, and a second impedance common to both of said paths, the ratio of said second impedance to said first impedance having a variation more rapid than the frequency 50 variation, and said impedances also being proportioned to produce substantially zero resultant transfer through the system at a frequency above the resonant frequency of said circuit.
  • an arrangement for reducing image frequency interference which comprises a coupling system including an input circuit, an output circuit, and two individual coupling means for coupling said circuits, one of said coupling means comprising 70 a first impedance means common to said input and output circuits, the other coupling means comprising a closed circuit tunable to a desired signal frequency, saidclosed circuit com a second impedance means also included in said a capacitive reactance element, one of said reactance elements being variable to tune said closed circuit, and said impedance means being so proportioned that image frequency interference produces in said output circuit equal and opposite voltages across said first impedance means and one of said reactance elements as said closed circuit is tuned to a desired signal frequency.
  • an arrangement for reducing image frequency interference which comprises a coupling system including an input circuit, an output circuit, and two individual coupling means for coupling said circuits, one of said coupling means comprising mutual coupling between said input and output circuits, and the other coupling means comprising a closed circuit tunable to a desired signal frequency, said closed circuit comprising impedance means common to said input circuit,
  • an arrangement for reducing image frequency interference which comprises a coupling system including an input circuit, an output circuit, and two individual coupling means for coupling said circuits, one of said coupling means comprising mutual inductance between said input and output circuits, and the other of said coupling means comprising a closed circuit tunable to a desired signal frequency, said closed circuit comprising afixed capacitive reactance element common to said input circuit, an inductive reactance element, and a capacitive reactance element variable to tune said tuned circuit, said mutual inductance and said fixed capacitive reactance element being so proportioned that the image frequency interference produces equal and opposite voltages across the inductance in said output circuit and the variable capacitive reactance element of said closed circuit, whereby image frequency voltages in said output circuit are substantially eliminated.
  • a coupling system including an input circuit, an output circuit, and two coupling means between said input and output circuits, one of said coupling means comprising a mutual inductance between said input and output circuits and including an inductance one end of which is at ground potential, and the other coupling means comprising a circuit tunable to a desired signal frequency, said tunable circuit comprising an inductance inductively related to said input circuit, a fixed capacityalso included in said input circuit, and a capacity variable to tune said circuit, the mutual inductance between said input and output circuits being so proportioned that the image frequency voltage developed across the inductance in said output circuit will be equal and opposite to that developed across the variable condenser common to said tuned and output circuits regardless of the tuning of said [tuned circuit, whereby image frequency voltages in said output circuit are substantially eliminated,
  • means for reducing image frequency interference which comprises a coupling system including an input circuit, an output circuit, and two individual coupling means for coupling said input and output circuits, one of said coupling means comprising a first impedance common to said input and output circuits, the other coupling means comprising a closed circuit tunable to a desired signal frequency; said closed circuit including a second impedance also included in said input circuit, an inductance, and a capacitance variable to tune the closed circuit; and said impedances being so proportioned that image frequency interference produces in the output circuit a voltage across the first impedance and a voltage across said capacitance, which voltages are substantially equal and opposite when the closed circuit is tuned to the desired signal frequency.
  • an arrangement for selectively coupling the antenna to succeeding circuits of said receiver and for reducing said interference comprising a primary circuit adapted to include said antenna, a secondary circuit coupled to said succeeding circuits and including a closed circuit tunable over said band, said closed circuit including reactances of opposite kinds, and two individual coupling means for select a signal of any desired frequency in a band coupling the ,antenna to succeeding circuits of said receiver and for reducing said interference comprising a primary circuit adapted to include said antenna, a secondary circuit coupled to said succeeding circuits, and two individual coupling means for coupling said circuits.
  • one of said means comprising a first impedance means common to said circuits, the other of said means comprising a closed circuit tunable over said band, said closed circuit including a second impedance means also included in said input circuit and additional reactance means, said impedances being so proportioned that image frequency interference produces in said secondary circuit equal and opposite voltages across said first impedance means and one of said additional reactance means when said closed circuit is tuned to a desired signal frequency, whereby image frequency voltages in said secondary circuit are substantially eliminated.
  • an antenna circuit broadly tuned to said band of frequencies whereby all signals having frequencies outside of said band are attenuated, and a selective circuit coupled between said antenna circuit and said receiver, said selective circuit comprising a resonant circuit coupled to said antenna circuit and to said receiverand sharply tunable selectively to transmit to said receiver any desired signal within said band of frequencies, and an auxiliary transfer means likewise coupled to said antenna circuit and to said receiver and operative to non-selectively transfer signal voltages throughout said band of frequencies, the coupling of said resonant circuit and said auxiliary transfer means to said receiver being so proportioned that they will deliver equal and opposite voltages to said receiver at any image frequency within said band and differing from the frequency to which said resonant circuit is tuned by a substantially uniform frequency diflference, whereby said selective coupling circuit suppresses all image frequency signals within said band.
  • a superheterodyne re- I DC having a permanently tuned intermediatefrequency amplifier, said receiver being tunable to any frequency in a band greater in width than twice the intermediate frequency; an antenna circuit permanently tuned within said band for attenuating undesired signals of frequencies outside said band, a resistance connected in said antenna circuit for broadening its resonance to include all of said band, and highly selective means and non-selective means each individually coupling said antenna circuit to the first vacuum tube of said receiver, said selective means comprising a resonant circuit tunable over said band, said non-selective means comprising fixed reactance independent of said resistance, adjusted to balance out image frequency signals within said band incidentally coupled to said receiver by said selective means, said image frequency differing by twice the intermediate frequency from the resonant frequency of said tunable circuit.
  • a selective coupling network which comprises; a primary circuit including connected in series a capacitive antenna, a fixed inductance and a fixed condenser; a secondary circuit including connected in series an adjustable condenser, another fixed inductance and said fixed condenser; and a third inductance inductively coupled to said first inductance connected in seties with the outputot said secondary circuit, said of signal channels, said secondary circuit being sharply tunable by said adjustable condenser to any frequency in said band, said first two. inductances being 0! thesame order of magnitude, and said fixed condenser having a capacitance on the order of ten times the capacitance of said adjustable condensers,

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Input Circuits Of Receivers And Coupling Of Receivers And Audio Equipment (AREA)
  • Superheterodyne Receivers (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
US590173A 1932-02-01 1932-02-01 Selective circuits Expired - Lifetime US2048527A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
BE393901D BE393901A (enrdf_load_stackoverflow) 1932-02-01
US590173A US2048527A (en) 1932-02-01 1932-02-01 Selective circuits
GB208/33A GB412942A (en) 1932-02-01 1933-01-03 Frequency selective filtering circuits
FR749563D FR749563A (fr) 1932-02-01 1933-01-26 Système de couplage électrique
DEH135012D DE749560C (de) 1932-02-01 1933-01-28 Kopplungsschaltung, besonders zur Unterdrueckung der Spiegelfrequenz in einem UEberlagerungsempfaenger

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US590173A US2048527A (en) 1932-02-01 1932-02-01 Selective circuits

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US2048527A true US2048527A (en) 1936-07-21

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US590173A Expired - Lifetime US2048527A (en) 1932-02-01 1932-02-01 Selective circuits

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US (1) US2048527A (enrdf_load_stackoverflow)
BE (1) BE393901A (enrdf_load_stackoverflow)
DE (1) DE749560C (enrdf_load_stackoverflow)
FR (1) FR749563A (enrdf_load_stackoverflow)
GB (1) GB412942A (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3593154A (en) * 1969-01-28 1971-07-13 Zenith Radio Corp Frequency-selective coupling network for a television tuner

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3593154A (en) * 1969-01-28 1971-07-13 Zenith Radio Corp Frequency-selective coupling network for a television tuner

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Publication number Publication date
FR749563A (fr) 1933-07-26
GB412942A (en) 1934-07-03
DE749560C (de) 1944-11-25
BE393901A (enrdf_load_stackoverflow)

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