US2212839A - High frequency tuned circuits - Google Patents

High frequency tuned circuits Download PDF

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Publication number
US2212839A
US2212839A US217124A US21712438A US2212839A US 2212839 A US2212839 A US 2212839A US 217124 A US217124 A US 217124A US 21712438 A US21712438 A US 21712438A US 2212839 A US2212839 A US 2212839A
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Prior art keywords
valve
condenser
grid
circuit
tuned
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Expired - Lifetime
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US217124A
Inventor
Lett Frederic Tom
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EMI Ltd
Electrical and Musical Industries Ltd
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EMI Ltd
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Publication of US2212839A publication Critical patent/US2212839A/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
    • H04B1/1638—Special circuits to enhance selectivity of receivers not otherwise provided for
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/01—Frequency selective two-port networks
    • H03H7/0153—Electrical filters; Controlling thereof
    • H03H7/0161—Bandpass filters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/01—Frequency selective two-port networks
    • H03H7/17—Structural details of sub-circuits of frequency selective networks
    • H03H7/1741—Comprising typical LC combinations, irrespective of presence and location of additional resistors
    • H03H7/1775—Parallel LC in shunt or branch path

Definitions

  • This invention relates to high frequency tuned c rcuits and has particular reference to the tuned clrcuits of modulated carrier wave receivers, the frequency band width of which it is desired to vary.
  • damping is imposed on a tuned circuit connected in the grid circuit of a valve when that valve has a largely capacitative load in its anode circuit.
  • the damping known as the Miller efiect, is a function of the magnification factor of the valve and also of its grid to anode capacity.
  • the object of the present invention is to provide an inexpensive but effective means of varying the selectivity of a tuned circuit in, for example, a wireless receiver provided with a screened grid valve or valves.
  • a condenser connected to the screening grid of the valve is arranged to be connected directly to earth or disconnected therefrom or to be connected to earth through a resistance which may be variable.
  • the condenser may constitute the usual de-coupling condenser and the valve may be a tun d radio or intermediate frequency amplifier or a detector valve, a. switch being provided for effecting the changes in the connections to the condenser.
  • a tuned circuit 3 which may be the output circuit of a radio or intermediate frequency amplifier is coupled to the tuned input circuit 2 of a screened grid detector valve 3 provided with a grid leak resistance and condenser E, 5.
  • the anode t of the detector valve 45 is coupled, for example through a resistance and shunt condenser E, 8, to a low frequency output circuit not shown and the screening grid 9 of the valve is connected through a resistance it to a source of high tension voltage.
  • a de-coupling condenser H is connected between the screening grid 9 and the cathode i2 through a variable resistance 13 across which is connected a switch M which enables the resistance to be short-circuited. This switch may, if desired, be arranged to leave the condenser open circuited.
  • the arrangement provides for variation of the selectivity of the tuned circuit am a simple manner by operation of the switch it to connect the de-coupling condenser ll directly to the cathode IE or through the resistance it.
  • the operating conditions, when the switch it is open and the resistance 53 effective, will be modified by the different effective anode impedance which obtains when the switch it is closed and the resistance i3 is short circuited.
  • the diiierent anode impedance will produce different damping effects upon the tuned circuit 2 with consequent differences in thebreadth of tuning.
  • Adjustment of the value of the resistance l3 provides a finer degree of variation oi selectivity. It is possible with the arrangement described to vary the damping applied to the tuned circuit 2 from 10,000 to 250,000 ohms due to the possible variations in the damping effect of the valve.
  • a circuit arrangement comprising in combination a thermionic valve having a cathode, an anode, a control grid and a screening grid, a tuned input circuit connected between said cathode and said control and means for varying the selectivity of said tuned input circuit, said means comprising a condenser connected to the screening grid of said valve, and means for selectively connecting said condenser directly or through an impedance to the cathode of said valve.
  • circuit arrangement comprising in combination a thermionic valve having a cathode, an anode, a control grid and a screening grid, 2. tuned input circuit connecting between said cathode and said control grid and means for varying the selectivity of said tuned input circuit, said means comprising a condenser and a resistance connected in series between the screening grid and cathode, and means for selectively short-circuiting said resistance.
  • a circuit arrangement comprising in combination a thermionic valve having a cathode, an anode, a control grid and a screening grid, 'a tuned input circuit connected between said cathode and said control grid and means for varying the selectivityof said tuned input circuit, said means comprising a condenser, and a variable resistance connected in series between the screening grid and cathode, and means for selectively short-circuiting said resistance.
  • valve constitutes an amplifier in a wireless receiver
  • condenser being a decoua wireless receiver
  • said condenser being a decoupling condenser for the screen grid of said valve and the selective short-circuiting means comprises a switch.
  • valve constitutes a detector valve in a wireless receiver
  • condenser being a decoupling condenser for the screening grid of said valve and the selective short-circuiting means comprises a switch.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Indication Of The Valve Opening Or Closing Status (AREA)

Description

Aug. 27, 1940. T LETT 2,212,839
HIGH FREQUENCY TUNED CIRCUITS Filed July 2, 1938 lA/VE/VTOR FEEDER/C 70M LET? BY ATTORNEY Patented Aug. 27, 1940 UNHE S signor to Electric &
Musical industries Limited, Hayes, Middlesex, England, a company of Great Britain Application July 2, 1938, Serial No. 217,124 In Great Britain July 14, 1937 7 Claims.
This invention relates to high frequency tuned c rcuits and has particular reference to the tuned clrcuits of modulated carrier wave receivers, the frequency band width of which it is desired to vary.
It is well known that damping is imposed on a tuned circuit connected in the grid circuit of a valve when that valve has a largely capacitative load in its anode circuit. The damping, known as the Miller efiect, is a function of the magnification factor of the valve and also of its grid to anode capacity.
The object of the present invention is to provide an inexpensive but effective means of varying the selectivity of a tuned circuit in, for example, a wireless receiver provided with a screened grid valve or valves.
According to the present invention in a circuit arrangement including a valve of the screened grid type having a tuned input circuit, in order to vary the selectivity of said tuned input circuit, a condenser connected to the screening grid of the valve is arranged to be connected directly to earth or disconnected therefrom or to be connected to earth through a resistance which may be variable. The condenser may constitute the usual de-coupling condenser and the valve may be a tun d radio or intermediate frequency amplifier or a detector valve, a. switch being provided for effecting the changes in the connections to the condenser.
In order that the invention may be more clearly understood and readily carried into effect, a portion of a circuit arrangement embodying the invention will now be described more fully by way of example with reference to the accompanying drawing.
Referring to the drawing a tuned circuit 3 which may be the output circuit of a radio or intermediate frequency amplifier is coupled to the tuned input circuit 2 of a screened grid detector valve 3 provided with a grid leak resistance and condenser E, 5. The anode t of the detector valve 45 is coupled, for example through a resistance and shunt condenser E, 8, to a low frequency output circuit not shown and the screening grid 9 of the valve is connected through a resistance it to a source of high tension voltage. A de-coupling condenser H is connected between the screening grid 9 and the cathode i2 through a variable resistance 13 across which is connected a switch M which enables the resistance to be short-circuited. This switch may, if desired, be arranged to leave the condenser open circuited.
I It will be seen that the arrangement provides for variation of the selectivity of the tuned circuit am a simple manner by operation of the switch it to connect the de-coupling condenser ll directly to the cathode IE or through the resistance it. The operating conditions, when the switch it is open and the resistance 53 effective, will be modified by the different effective anode impedance which obtains when the switch it is closed and the resistance i3 is short circuited. The diiierent anode impedance will produce different damping effects upon the tuned circuit 2 with consequent differences in thebreadth of tuning. Adjustment of the value of the resistance l3 provides a finer degree of variation oi selectivity. It is possible with the arrangement described to vary the damping applied to the tuned circuit 2 from 10,000 to 250,000 ohms due to the possible variations in the damping effect of the valve.
I claim:
l. A circuit arrangement comprising in combination a thermionic valve having a cathode, an anode, a control grid and a screening grid, a tuned input circuit connected between said cathode and said control and means for varying the selectivity of said tuned input circuit, said means comprising a condenser connected to the screening grid of said valve, and means for selectively connecting said condenser directly or through an impedance to the cathode of said valve.
' A. circuit arrangement comprising in combination a thermionic valve having a cathode, an anode, a control grid and a screening grid, 2. tuned input circuit connecting between said cathode and said control grid and means for varying the selectivity of said tuned input circuit, said means comprising a condenser and a resistance connected in series between the screening grid and cathode, and means for selectively short-circuiting said resistance.
3. A circuit arrangement comprising in combination a thermionic valve having a cathode, an anode, a control grid and a screening grid, 'a tuned input circuit connected between said cathode and said control grid and means for varying the selectivityof said tuned input circuit, said means comprising a condenser, and a variable resistance connected in series between the screening grid and cathode, and means for selectively short-circuiting said resistance.
4. A circuit arrangement according to claim 1 wherein said valve constitutes an amplifier in a wireless receiver, said condenser being a decoua wireless receiver, said condenser being a decoupling condenser for the screen grid of said valve and the selective short-circuiting means comprises a switch.
7. A circuit arrangement according to claim 2 wherein said valve constitutes a detector valve in a wireless receiver, said condenser being a decoupling condenser for the screening grid of said valve and the selective short-circuiting means comprises a switch.
FREDERIC TOM LETT.
US217124A 1937-07-14 1938-07-02 High frequency tuned circuits Expired - Lifetime US2212839A (en)

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GB2212839X 1937-07-14

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2568137A (en) * 1948-02-12 1951-09-18 Zenith Radio Corp Demodulator
US2838616A (en) * 1953-04-17 1958-06-10 Western Union Telegraph Co Repeater amplifier

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2568137A (en) * 1948-02-12 1951-09-18 Zenith Radio Corp Demodulator
US2838616A (en) * 1953-04-17 1958-06-10 Western Union Telegraph Co Repeater amplifier

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