US1820809A - Electrical system - Google Patents

Description

' Aug. "2511531;

Filed March 25, 192'? FLgJ.

III'IIIIIIL- E Inventor: Edward \XAKeIlogg.

- Patented Aug. 25, 1931 UNITED STATES PATENT OFFICE i EDWARD W. KIElLLOGG, OF SCHENEC'IADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK Mormon. sYs'rEm Application filed larch 25, 1927. Serial No. 178,476.

My invention relates to electrical systems comprising a space discharge device having its input circuit connected to an antenna through a local high frequency source, and

has for its principal object the provision of an im roved arrangement whereby the feeding 0 energy from the input circuit into the antenna may be prevented.

In heterodyne systems comprising an antenna and a local source or oscillator operated at a frequency slightly different from that of the antenna for producing a low frequency beat voltage, it 1s customary to connect the oscillator, or a coil inductively com pled thereto, in series with the antenna tuning coil, between the cathode and the grid of the space discharge device so that the oscillator voltage plus the antenna voltage is applied between the' grid and cathode of the device. In producing a voltage between grid and cathode of the space discharge device, the local source or oscillator incidentally impresses a voltage across the antenna tuning. The oscillator voltage is in fact divided between the two circuit elements, antenna tuning and grid to cathode capacity, and the fraction of the oscillator voltage which is impressed across the antenna tuning depends on the impedance drops through two different parts of the circuit. The grid to cathode capacity reactance is of the order of 10,000

ohms at broadcasting wavelengths. The impedance of the tuned antenna circuit varies from a few hundred ohms when the oscillator is operated at a frequency substantially dilferentfrom that for which the antenna is tuned to from 10,000 to 40,000 ohms when the oscillator frequency is substantially the same as that for which the antenna is tuned.

As long as the frequency of the oscillator is substantially different from that for which the antenna is tuned, there is little variation in the antenna voltage produced by adjustment in the frequency of theoscillator. In the operation of tuning in stations, however, the frequency of the oscillator frequently crosses that for which the antenna is tuned and the antenna voltage is varied in a manner to interfere with other receiving sets.

5 In accordance with my invention, this difnassueo ficulty is avoided by connecting the oscillator to the input circuit in such a waythat the potential of the grid with respect to ground I (assuming one end of the antennatuning coil' to be grounded) is substantially unaffected by the oscillator voltage, while the necessary a cathode to grid voltage is obtained by causing the cathode to vary in potential with re-,

spect to ground, at oscillator frequency.

My invention will be better'understood from the following description when considered in connection with the accompanying drawings and its scope will bepointed out in Y the appended claims.

, Referring to the drawings, Fig. 1 diagram:

matioally illustrates a heterodyne system wherein my invention has been embodied; and Figs. 2 and 3 illustrate its application to slightly different autodyne systems.

Fig. 1 shows a detector devicel which is provided with an input circuit comprising a grid 2, a cathode 3, a double-wire secondary' winding 40f a transformer 5, and a tunin element 6 connected between an antenna f -er 9 and a transformer winding 10, and an anode 11. A, local source of oscillations or oscillator 12 is connected to the input circuit of the device 1 through a primary winding 13 and the secondary winding 4 each turn of which is made of double wire in order to permit the transmission of heating current to the anode 3 froma source 14 through a control resistor 15. A winding 16, inductively related to the winding 13, is connected to the grid 2 or high potential end of the input circuit through a condenser 17 for the purpose of neutralizing the effect of the capacity couplixnlg between the grid 2 and the cathode 3.

ith these connections, the oscillator 12 causes the potential of the cathode 3 to change with respect to ground or low potential end of the input circuit but produces little, if any, effect on the potential of the grid 2. Since the anode 11 is virtually grounded through "the" intermediate frequency tuning -condenser 9, there is no tendency for currents of oscillator'frequency to get into the antenna circuit by way of'th'e grid to anode capacity. J The potential of the antenna 7 with i' respect to ground is thus substantially un zifiectedby the oscillator and interference with-other receivingis avoided.

f Fig; 2 illustratesfan autodyne system wherein a' resistor 18 is connected in the oscillator circuit topermit adjustment in in- Y tensity of'the'oscillations. V In the case of the "autodyn'e' circuit, an appreciable impedjprevious' case. Under these conditions the balancing condenser 17 would need to be reance at oscillator frequency is introduced by the feed back coil in the anode circuit, and 'thereforethe anode is no longer maintained at practically stationary potential as in the adjusted in orderfthat it might balance out the electrostatic effect on the grid. of both cathode'and anode capacities. If the cou- 'pling'beti'veen coil '5 and coils 4 and 16 can be maintained constant, theratio between cathode'and anode voltages at oscillation. frequency will remain substantially constant,

and a single setting of condenser 17 will suffice for balancing outthe electrostatic effects otboth anode and cathode on the grid potenti'al. The rheostat 18 provides means whereby the amount of feed back can be con- 'trolledwithout 'changing'the coupling between coil 13-and coils4'and16. It should be bornein mind in following this discussion that the output circuit 9,10, istuned for a frequency which differs-widely from the os cillation frequencyand has negligible impedance for 1 the oscillation currents.

If it is desired to maintain the rheostat 18 at constant potential, the oscillator-tuned circuit maybe connected in series with themtermediate tuning condenser 9' as shown 1n Fig. 3.

The embodiments of the invention illustrated and described herein have been se-' lected for the purpose of clearly setting forth the principles involved. It will be apparent,

' however, that the invention is susceptible of being modified to'meet the dilterent conditionsencounteredinits use. For example the circuit 6-7 which is represented as an antenna, mightinstead, be a receiving loop,

and it isnot necessary to have any part of the circuit actually grounded, the ground'indicatedin'the drawings being primarily a reference potential. It is also apparent that where the cathode is of the radiation heated type rather than the hot filament type, the coil would not have to be of double wire. I therefore aim to cover by the appended claims all modifications within the truespirit and scope ofmy invention.

What I'claim as new and desire to secure by Letters Patent of the United'States. is 1. A radio apparatus of the heterodyne type including a detector tube, an input circuit for said-tube having a low potential end connected with the cathode of the tube for impressing a signal voltage upon said tube, an output circuit'tor said tube,.means providing a common grounded connection between said output circuit and said low potential endof said input circuit, a source of oscillations, and means coupled with said source and'interposed in'circuitbetween the low potential end of the input circuit and said cathode for causing the cathode potential to varywith respect to'the low potential end of said input 'circuit.

2. A radio apparatus of the heterodync type including a detector tube, an input circuit for said tube having a low potential end connected with the cathode of the tube for impressing a signal voltage upon said tube,

an output circuit for said tube, means providing a common grounded connection between. said output circuit and said low potential end of said inputcircuit, a source of oscillations, means coupled with said source and interposed in circuit between the low potential end of the input circuit and said ing a grid, a cathode and an anode, and a tuned'mput circuit connected between said grid and cathode, of means for impressing the oscillations of said source upon said device without radiating the same from said tuned circuit, including a ground connec tion for said'input circuit, a transformer having a primary winding connected with.- said source and a secondary winding 1nter-.

posed in circuit between the cathode and'the ground connection.

- 4. In an electrical apparatus of the high frequency heterodyne type, the combination withan'electric discharge device having a grid, an anode and a cathode, of a ground connection, an input signal voltage circuit for said device connected between the ground connection and the grid of said device, an

output circuit connected between the ground connection and the anode, and means for applying an oscillation voltage at a difierent frequency from the signal voltage interposed between the ground connection and the cathode.

5. In an electrical apparatus of the high frequency, heterodync type, the combination with an electric discharge device having a grid, an anode aniid a cathode, of a ground connection, aniiiput signal voltage circuit for said device connected between the ground connection and the grid of said device, an output circuit connected between the ground connection and the anode, means for applying an oscillation voltage between the ground connection and the cathode, and means connected between the ground connection and the grid of said device for neutralizing the connected between the ground connection and the anode, means for applying an oscillation voltage at a different frequency from the signal voltage between the ground connection and the cathode, and means for tuning said input and output circuits.

In an electrical apparatus of the high frequency, heterodyne type, the combination with an electric discharge device having a grid, an anode and a cathode, of a ground connection, an input signal voltage circuit for said device connected between the ground connection and the grid of said device, an output circuit connected between the ground connection and the anode, and meansjor applying an oscillation voltage between the ground connection and the cathode, and

, means for adjusting the intensitv of the oscillation voltage applied from said source.

8. The combination with an electric discharge device of the self-heterodyne type having a grid. an anode, a cathode. an input circuit connected with the grid and an output anode circuit, of means for applying selfheterodyne oscillations to said device, said means including a transformer having a primary connected in said output circuit, means connected in circuit with the primary for varying the frequency of the self-heterodyne oscillations, means in circuit with the primary for varying the strength of said oscillations, a secondary for said transformer, said secondary providing a common connection between said input and output circuits and the cathode of said device, and a neutralizing means including a winding inductively coupled with said primary connected in parallel with the input circuit.

9. The method of heterodvning a radio signal which comprises applying asignal voltage at a certain frequency between the grid of an electric discharge device and ground, and simultaneously applying an oscillation voltage at a different frequency between ground and the cathode of said device.

10. The method of heterodyning a radio signal which comprises applying a signal voltage at a certain frequency between the grid of an electric discharge device and ground, neutralizing the inter-e1ectrode capacity of the device, and simultaneously applying an oscillation voltage at a different frequency between ground and the cathode of said device.

In witness whereof, I have hereunto set my hand this 24th day of March 1927.

EDWARD W. KELLOGG..

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