US2531301A

US2531301A - Circuit arrangement for frequency controls

Info

Publication number: US2531301A
Application number: US675023A
Authority: US
Inventors: Scholten Egbert
Original assignee: Hartford National Bank and Trust Co
Current assignee: Hartford National Bank and Trust Co
Priority date: 1945-02-08
Filing date: 1946-06-07
Publication date: 1950-11-21
Anticipated expiration: 1967-11-21
Also published as: BE458146A; GB607798A; CH256375A; FR923304A

Description

Npv. 21, 1950 E. SCHOLTEN CIRCUIT-ARRANGEMENT FOR FREQUENCY CONTROLS Filed June 7, 1946 1NVENTOR.-

EGBERT SCHOLTEN BY A ATTORNEY Paten tecl Nov. 21, 1950 UNITED STATES r.

TENT OFFICE CIRCUIT ARRANGEMENT FOR FREQUENCY CONTROLS Application June 7, 1946, Seriai No. 675,023 In Belgium February 8, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires February 8, 1965 6 Claims. (Cl. 250-36) This invention relates to a circuit-arrangement for controlling with the aid of a control magnitude the frequency of electrical oscillations generated by means of a discharge system, this circuit being particularly suitable for keeping constant the frequency of telegraphy transmitters and for the production of frequency-modulated oscillations.

Circuit-arrangements are known in which the frequency of the electrical oscillations produced by an oscillator is controlled in accordance with the value of a control voltage, a so-called reactance tube being used. Such a tube which may be connected in parallel with the resonant circuit of the oscillator behaves as a reactance depending upon the mutual conductance. To this end the tube is connected in such a manner that the alternating voltage of the grid, to which the control voltage is supplied and the anode voltage of the tube exhibit a phase-difference of about 90.

These circuits have the drawback that, if the frequency of the oscillations produced should be variable through a fairly considerable range, the power of the reactance tube should be of the same order of magnitude as that of the oscillator tube. With a high power oscillator use should consequently be made of a reactance tube capable of absorbing a high power which is not economical.

The invention procures a circuit-arransement which permits the frequency of the oscillations produced to be varied through a comparatively broad range, without an additional high power tube being needed. According to the invention the frequency of the oscillations produced is controlled by inserting an impedance in a lead to a control-electrode of the aforesaid discharge system, the magnitude of this impedance varying with the control magnitude.

Use is preferably made of a discharge tube to constitute the impedance, which tube is controlled by the control magnitude (control voltage, modulation voltage). Thus a simple circuit ensues, in which a comparatively low power discharge tube permits the frequency to be controlled over a wide range.

If the invention is used in a circuit-arrangement for keeping constant the frequency of the electrical oscillations produced by means of a discharge system, the said impedance or the said discharge tube can effectively be controlled by means of a control voltage initiating from a frequency detector to which the produced oscillations are supplied.

In order that the invention may be clearly understood and readily carried into effect, it will now be explained more fully with reference to the accompanying drawing, in which one form of construction thereof is represented by way of example.

Referring to the drawing there is shown an oscillator circuit having an electron discharge tube I, which in the present example is shown as a triode, by means of which the electrical oscillations are produced whose frequenc is kept at a constant value. The anode-circuit of tube l includes a resonant circuit 2 which is inductively coupled with a back-coupling coil 3 which is inserted, in series with a condenser 4, in the control-grid circuit of tube I.

According to one embodiment of the invention the lead from the control grid to the oathode of tube I includes a discharge tube 5. In series with tube 5 are connected a cathode resistance 6 and a choke I; the series-

connection

5, 6 and '5 functions as a leakage resistance for the discharge tube I. Furthermore, the grid circult of tube 5 comprises a grid leakage resistance 8. A condenser 9 shunts the tube 5 in regard to currents of the oscillations generated. The frequency of the electrical oscillations produced by the oscillatory system I, 2, 3, 4 is controlled by varying the resistance of tube 5. This is effected by means of a control voltage which is supplied to the control grid of tube 5 and more particularly to the terminals designated by ID.- In the present case this control voltage is taken from a frequency-detector H to which the oscillations generated by the circuit 2 are applied, for example, by means of a Winding IL.

The operation of the circuit is based on the fact that the frequency of the oscillations generated by means of a discharge tube by backcoupling depends, inter alia, upon the value of the grid-current, so that by controlling the value of this current (which in the present case takes place by controlling the value of the leakage resistance) the frequency of the oscillations is affected.

The influence of the value of the grid current on the frequency of the oscillations generated can. be increased by causing a phase-displacement materially differing from to take place between the voltages set up at the oscillator electrodes of the discharge system. For thispurpose the back-coupling circuit of the present arrangement comprises a phase-shifter which, in the case under view, consists of the condenser 4- and the internal resistance between grid andcathode of the tube I. In conjunction therewith the condenser 4 is a condenser having a low capacity (for example about 40 micromicrofarads at a frequency of 3 mc./s., whereas the normal value is 300 micromicrofarads) Owing to the phase-displacement brought about by the element the frequency of the oscillations generated no longer coincides with the resonance frequency of the resonant circuit 2. In fact, this adjusts itself so far from the resonance frequency that across the circuit 2 occurs a substantially as great, but opposite phase displacement as across the back-coupling circuit. If, consequently, the magnitude of the phasedisplacement across the back-coupling circuit is changed, the frequency of the oscillations generated varies at the same time.

By control of the direct grid current of tube I, which in the circuit-arrangement shown is effected by controlling the resistance of tube 5, the internal resistance between grid and cathode of the tube is varied; as a result thereof the phase-displacement across the back-coupling circuit. varies (i. e. the phase of the alternating control-grid voltage) which, as has been set out above, brings about a variation of the frequency of the oscillations generated.

At a control voltage of volt the frequency of the oscillations generated is adjusted approximately at the centre of the desired control range. This may, for instance, occur by adjustment of the cathode resistance 6 or by giving the control tube a suitable bias.

Now, if the control voltage assumes a value deviating from zero, the value of the leakage -resistance constituted by the control tube 5 varies likewise, with the result that the frequency of the oscillations generated by means of the oscillator tube I is varied. The control voltage should, of course, be supplied to the terminals l0 in such a manner that, if for example, the frequency of the oscillations generated should tend to increase, the resistance variation of tube 5 shows a tendency to counteract this frequency increase.

The circuit-arrangement may advantageously be used for keeping constant the frequency of telegraphy transmitters, since the frequency of the oscillations transmitted varies due to the signalling. These frequency variations can be suppressed completely or substantially completely by using this circuit-arrangement.

The invention may also be used to generate frequency-modulated electrical oscillations. In this case the modulation voltage may effectively be supplied to the terminals ll) of the circuit shown in the drawing.

It may still be observed that by controlling the internal resistance of tube 5 the direct grid current of tube I is varied, but the direct grid voltage of this tube remains substantially constant. If, consequently, the circuit-arrangement is used for the production of frequency-modulated oscillations a highly linear, distortion-free frequencymodulation is ensured without a material amplitude-modulation occurring.

What I claim is:

'1.A' 'circuit'arrangement for varying'the frequencyof an oscillator in response to variations of a control voltage, comprising an oscillator tube having an anode, a control grid and a cathode, a resonant circuit coupled between the anode and cathode'of'said oscillator tube to determine the frequency of'said oscillator, a coil inductively coupled to said resonant circuit; means coupling said coil between the grid and cathode of said oscillator tube to couple the grid in feedback relationship substantially out of phase with respect to the anode of said oscillator tube, a variable impedance element coupled between the cathode and the control grid of said oscillator tube, and means responsive to said variations of said control voltage to vary the impedance value of said impedance element thereby to effect a shift in phase away from said 180 relationship and vary the frequency of said oscillator.

2. A circuit arrangement for varying the frequency of an oscillator about a determined frequency value in response to variations of a control voltage, comprising an oscillator tube having an anode, a control grid and a cathode, a resonant circuit coupled between the anode and cathode of said oscillator tube to determine the frequency of said oscillator, a coil inductively coupled to said resonant circuit, a capacitor coupling said coil between the grid and cathode of said oscillator tube to couple the grid in feedback relationship to the anode of said oscillator tube, a control tube having an anode, a grid and a cathode, the anode of said control tube being coupled to the cathode of said oscillator tube, a first resistor, a second capacitor, means to connect said first resistor and said second capacitor in series between the grid of said control tube and the cathode of said oscillator tube, means to apply said control voltage across said first resistor, a second resistor, an inductor, and means to connect said second resistor and said inductor in series between the cathode of said control tube and the control grid of said oscilator tube to vary the impedance across the grid and cathode of said oscillator tube in response to said variations of said control voltage thereby to vary the frequency of said oscillator about said determined value.

3. A circuit arrangement for maintaining the frequency of an oscillator constant at a given value in response to a control voltage having variations'proportional to the frequency deviations of said oscillator, comprising an oscillator tube having an anode, a control grid and a cathode, a resonant circuit coupled between the anode and cathode of said oscillator tube to determine the frequency of said oscillator, a coil inductively coupled to said resonant circuit, a capacitor coupling said coil between the anode and cathode of said oscillator tube to couple the grid in feedback relationship to the grid of said oscillator tube, a control tube having an anode, a grid and a cathode, the anode of said control tube being coupled to the cathode of said oscillator tube, a first resistor, a second capacitor, means to connect said first resistor and said second capacitor in series between the grid of said control tube and the cathode of said oscillator tube, means'to apply said control voltage across said first resistor, a second resistor, an inductor, and means to connect said second resistor and said inductor in series between the cathode of said control tube and the control grid of said oscillator tube to vary the impedance across the grid and cathode of said oscillator tube in response to said variations of said control voltage thereby to maintain the frequency of said oscillator constant at said given frequency value.

4. A circuit arrangement for maintaining the frequency of an oscil ator constant at a given frequency value, comprising an oscillator tube having'an anode. a control grid and a cathode, a resonant circuit coupled between the anode and cathode of said oscillator tube to determine the frequency of said oscillator, a coil inductively coupled to said resonant circuit, a capacitor coupling said coil between the grid and cathode of said oscillator tube to couple the grid in feedback relationship to the anode of said oscillatortube, a frequency responsive detector coupled to said resonant circuit to derive a potential proportional to the frequency deviation from said given frequency value, a control tube having an anode, a grid and a cathode, the anode of said control tube being coupled to the cathode of said oscillator tube, a first resistor, a second capacitor, means to connect said first resistor and said second capacitor in series between the grid of said control 1 tube and the cathode of said oscillator tube, means to couple said frequency responsive detector across said first resistor to apply said potential thereto, a second resistor, an inductor, and means to connect said second resistor and said inductor in series between the cathode of said control tube and the control grid of said oscillator tube to vary the impedance across the grid and cathode of said oscillator tube in proportion to said potential thereby to maintain the frequency of said oscillator at said given value.

5. A circuit arrangement for maintaining the frequency of an oscillator constant at a given frequency value, comprising an oscillator tube having an anode, a control grid and a cathode, a resonant circuit coupled between the anode and cathode of said oscillator tube to determine the frequency of said oscillator, a coil inductively coupled to said resonant circuit, a capacitor coupling said coil between the grid and cathode of said oscillator tube, a frequency responsive detector coupled to said resonant circuit, a control tube having an anode, a grid and a cathode, the anode of said control tube being coupled to the cathode of said oscillator tube, a first resistor, a second capacitor, means to connect said first resistor and said second capacitor in series between the grid of said control tube and the cathode of said oscillator tube, means to couple said frequency responsive detector across said first resistor, a second resistor, an inductor, and means to connect said second resistor and said inductor in series between the cathode of said control tube and the control grid of said oscillator tube.

6. In an oscillator circuit arrangement in which the oscillator is adapted to be controlled by application of a control voltage, the combination comprising an oscillator tube having an anode, a cathode and at least one control grid, a resonant circuit coupled between the anode and cathode of said oscillator tube to determine the basic frequency of the oscillator, means coupling the anode in feedback relationship to the grid of said oscillator tube, a reactance element interposed in the feedback path between the anode and the grid of said tube and having a given reactance value, an auxiliary grid-controlled discharge tube hav- 7 ing a variable impedance of the same order of magnitude as aid given reactance value coupled 7 between the cathode and grid of said oscillator tube, and means to apply said control voltage to said auxiliary grid-controlled tube whereby the frequency of said oscillator varies in response to said control voltage.

EGBERT SCHOLTEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,683,012 Appleby Sept. 4, 1928 1,997,084 Roosenstein Apr. 9, 1935 2,265,016 White Dec. 2, 1941 2,349,885 Roberts May 30, 1944 2,397,701 Smyth Apr. 2, 1946 FOREIGN PATENTS Number Country Date 166,594 Great Britain July 11, 1921 Certificate of Correction Patent N 0. 2,531,301 November 21, 1950 EGBERT SCHOLTEN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: 7

Column 4, line 51 for anode read m'd; line 53, for rid read (mode a 9 g and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice. Signed and sealed this 30th day of January, A. D. 1951.

THOMAS F. MURPHY,

Assistant Gammz'ssz'oner of Patents.