US2064991A - High frequency amplifying system - Google Patents

High frequency amplifying system Download PDF

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Publication number
US2064991A
US2064991A US543140A US54314031A US2064991A US 2064991 A US2064991 A US 2064991A US 543140 A US543140 A US 543140A US 54314031 A US54314031 A US 54314031A US 2064991 A US2064991 A US 2064991A
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United States
Prior art keywords
circuit
valve
high frequency
input
coil
Prior art date
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Expired - Lifetime
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US543140A
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English (en)
Inventor
Round Henry Joseph
Turner Philip Keston
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RCA Corp
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RCA Corp
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Publication date
Application filed by RCA Corp filed Critical RCA Corp
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Publication of US2064991A publication Critical patent/US2064991A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/16—Circuits
    • H04B1/163—Special arrangements for the reduction of the damping of resonant circuits of receivers

Definitions

  • the invention has for its object to provide an amplifying system wherein great amplification and sharp selectivity may be obtained by the use of what is sometimes termed retroaction, without the defects normally experienced when an attempt is made with known arrangements to increase retroaction to a large extent.
  • retroaction i. e. to feed back energy from the output circuit of one of the valves to the input circuit .Of a previous valve.
  • that part of the amplifier which is between the two valves which are retroactively coupled is of a frequency selective nature, e. g., if it includes tuned circuits, the effect of retroaction is not only to increase the apparent amplification, but also the apparent selectivity, the latter effect being often somarked that unless special means be taken to correct for it, serious distortion of any complex modulation which the incoming signals may carry occurs.
  • modulation may be regarded as equivalent to the addition to the main sinusoidal radio frequency current (the carrier) of other frequencies (side band frequencies) if the selectivity is unduly sharp the side bands and the carriers are not equally amplified, and the result, after rectification, .is that currents of lower modulating frequencies, i. e., those frequencies which, in the complex wave before rectification, are nearest the carrier, are disproportionately large as compared with currents of higher modulating frequencies.
  • a first requirement in obtaining great amplification by retroaction is that the fed back energy shall be strictly proportional to the energy coming in from the external source (e. g. the energy received upon a broadcast receiving aerial), for it is a condition necessary for great amplification that the energy fed back must be nearly, though not quite, sufficient to maintain the appropriate circuit in permanent oscillation. It follows, therefore, that if an increase of input from the external source causes a disproportionately large increase in feed-back, the circuit in question may break into oscillation if the input voltage (e. g. the received strength) be strong. In practice, the obtaining of the required proportionality depends upon the valves having linear characteristics, and, of course, the characteristics of valves are practically never absolutely linear.
  • a thermionic amplifying circuit comprises a thermionic valve of comparatively high mutual conductance, a tuned circuit associated with the input electrodes of said valve in such manner that the voltage transferred to the said electrodes from the said tuned circuit is only a small proportion of the tot-a1 voltage set up across said tuned circuit, and means for applying reaction between the output and input circuits of said valve, the whole arrangement being such that the action of the valve under impressed signals is substantially linear, and the degree of reaction employed is sufficient to bring the whole circuit arrangement effectively almost to zero resistance.
  • the grid of the valve is "tapped down on the tuned input circuit, so that only a portion and preferably only a small portion of the voltage across the said tuned circuit is actually fed down to the grid.
  • v is a reaction valve receiving voltage from the usual tuned circuit 10.
  • the grid g of the valve is tapped down as shown, by means of a tapping #3 upon the inductance l of the'tuned circuit.
  • the plate circuit of the valve contains a reaction coil re 7 which is coupled to the coil 2. Connections ww are taken, as shown, from the ends of the tuned circuit 10, these connections being led to the input circuit of the usual detector, not shown.
  • Another requirement for high amplification by retroaction is that the fed backvoltage shall be exactly in phase with that existing in the circuit, for if the fed back voltage wave lag or lead by some phase angle upon the voltage wave already present, the maximum amplification obtainable by retroaction can, as may be shown mathematically, neverexceed the cosecant of that angle. Thus, if the lag or lead were only 2", the limiting amplification before self oscillation occurs is approximately 28.5 times.
  • Fig. 2 An arrangement of this kind is shown in Fig. 2,- in which, asv will be seen, the steady nected between the anode and filament of the valve and is tuned to the radio frequency so as to offer as nearly as possible zero reactance at that frequency.
  • the coil T0 in this tuned circuit is weakly coupled to the coil Z in the input circuit of the valve, so as to induce therein the required feed back voltage.
  • a pushpull circuit may be resorted to.
  • a simple way of meeting this difficulty is to incorporate circuits in accordance with this invention in an intermediate frequency amplifier operating at constant frequency and following a wave changer as in the well known supersonic heterodyne circuit.
  • a variable resistance or reactance whose control member is mechanically coupled with the tuning control member and which is arranged to apply the necessary compensation to maintain correct retroaction adjustment over the whole tuning frequency band.
  • this effect may be achieved without mechanical coupling.
  • tuning is effected by inductance variation alone, the capacity and resistance remaining constant, and the mutual inductance between the tuning. and retroaction coils, also remaining constant, constancy of the retroaction adjustment over the whole frequency. tuning band will'be automatically achieved.
  • a high frequency resonant circuit including an inductance coil, a tube having its input electrodes connected across a portion of said coil, a source of anode potential for the tube, a path between the anode of the tube and its cathode including a coil and a variable condenser, said coils being coupled, connections for connecting said circuit to the input of a detector and a capacitative neutralizing path connected between the anode and resonant circuit.
  • a tube having its input electrodes connected across a part or" the circuit, a path coupling the anode circuit of the tube to said resonant circuit whereby high frequency energy is regeneratively fed back from the anode circuit of the tube to said input circuit, means in said path including a coil and a serially connected condenser resonating the path to the frequency of said resonant circuit whereby the voltages of the fed back energy and the resonant circuit energy are in phase, and a capacitative neutralizing path connected between anode and resonant circuit.
  • a tube having its cathode connected to an intermediate point on the input circuit inductance and its input electrode connected to said inductance at a point spaced from the cathode connection, a circuit including a coil inductively coupled to the tunable input circuit and a variable condenser, said coil and condenser being serially connected between the anode and cathode of the tube, and a neutralizing condenser connected between the tube anode and a point on the input circuit inductance also spaced from the cathode connection, said condenser and grid connecting points on the inductance being on opposite sides of the cathode connecting point.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Amplifiers (AREA)
US543140A 1930-06-12 1931-06-09 High frequency amplifying system Expired - Lifetime US2064991A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB18111/30A GB358932A (en) 1930-06-12 1930-06-12 Improvements in or relating to high frequency amplifying systems

Publications (1)

Publication Number Publication Date
US2064991A true US2064991A (en) 1936-12-22

Family

ID=10106835

Family Applications (1)

Application Number Title Priority Date Filing Date
US543140A Expired - Lifetime US2064991A (en) 1930-06-12 1931-06-09 High frequency amplifying system

Country Status (4)

Country Link
US (1) US2064991A (de)
BE (1) BE380510A (de)
FR (1) FR718493A (de)
GB (1) GB358932A (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2675432A (en) * 1950-04-04 1954-04-13 Rca Corp Regenerative feedback circuit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2675432A (en) * 1950-04-04 1954-04-13 Rca Corp Regenerative feedback circuit

Also Published As

Publication number Publication date
FR718493A (fr) 1932-01-25
GB358932A (en) 1931-10-12
BE380510A (de)

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