US2137687A - Oscillation generator - Google Patents

Description

Nov. 22, 1938. c w HANSELL 2,137,687

050 ILLATION GENERATOR Filed March 20, 1937 'INVENTOR a Mz-wc'f n4 M/VSHL BY f4 ATTORNEY Patented Nov. 22, 1938 PATENT oFFicE v OSCILLATION GENERATOR Clarence W. Hansell, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March 20, 1937, Serial N... 132,040

3 Claims.

My present invention relates to constant frequencyoscillation generators and particularly to crystal controlled oscillation generators. That part of the instant disclosure which relates to Fig. 2 of the drawing forms the subject matter of a divisional application Serial No. 234,521 which was filed October 12, 1938.

Crystal controlled oscillation generators are generally employed to control transmitters so that the emitted waves correspond in frequency to the frequencies allotted to them. Unfortunately, transmitter operators frequently cannot resist the temptation to adjust or otherwise alter the tuning and other adjustments of crystal controlled generators, thereby unwittingly causing transmission at undesired wave lengths. One object of my present invention is, accordingly, to provide an oscillation generator which is substantially fool proof and which, even though tuning adjustments are altered, continues to operate at the desired operating frequency or, rather than operate at some unassigned frequency, ceases to operate entirely.

In efiecting this object, I provide a generator which will oscillate efliciently at the correct frequency with the frequency controlling circuit, such as a crystal, short circuited. Arrangements are made so that when the short circuit is removed, the frequency controlling circuit or the crystal is inserted effectively in series with an oscillating circuit of the generator. If the generator adjustments or settings are changed in any way so as to cause a frequency departure away from the natural frequency of the frequency controlling circuit, the frequency controlling circuit, rather than act as a short circuit, serves to inject high reactance in the generator system causing a return to the desired frequency or such losses as to cause cessation of operation, as will be explained more fully hereinafter.

My present invention is described more fully with the aid of the accompanying drawing in which Figure 1 is a wiring diagram of a pushpull oscillation generator employing the feattures of my present invention, and Figure 2 illustrates a single tube modification of my present invention.

Turning to Figure 1, tubes 2, 4 are provided with a tunable plate circuit 6 having a tuning condenser 8 and an output coil l0. Plate voltage is supplied through the choke coil l2 provided with a high frequency by-passing condenser II.

The grid circuit for the tubes 2, 4 includes a tuning condenser l6 and coils I8, 20 which may be made variable if desired.

Cross connected neutralizing condensers 22, 24 are provided which are adjusted for either over or under neutralization of such a value as to cause oscillation generation to take place. The regeneration for oscillation generation may not 5 only be provided by the tuning of condensers 22, 24, but in the alternative or in addition may be varied by tuning the anode circuit 8, I0 or the grid circuit [6, I8, 20. The grid coil system I8,

20 is divided and connected therebetween is a 10 frequency controlling circuit in the form of a piezo-electrical crystal 26. In series with the crystal electrodes there are provided coils 28, 30 and in shunt to these coils are connected resistors 32, 34.

A switch, not shown, may be provided to short circuit the crystal and coils 28, 30.

In accordance with this invention, the crystal and coils 28, 30 are first short circuited and the system tuned and otherwise adjusted as to plate 20 voltage and filament heating current so as to oscillate efliciently at the correct frequency. Then, by removing the short circuit, the crystal and the two adjustable coils 3|], 28 are effectively inserted in series with the grid oscillating cir- 25 cuit comprising coil l8, condenser l6 and coil 20. The crystal, ground to oscillate at the desired operating frequency, is thereby an effective short circuit at the desired frequency and does not alter the frequency of operation of the gener- 30 ating system as before adjusted. The small inductances 3|], 28, shown in series with the crystal 26, may be provided to tune out electrode to crystal capacity and/or the entire crystal holder capacity so that the crystal will act as a tuned short 35 circuit even more closely to its natural mechanical resonant frequency.

If the circuits change in frequency as, for example, should the condensers 8 and/or I6 be turned, the crystal will present a high reactance of a kind which tends to reduce the change in oscillation frequency. At the same time, the reactance will cause currents to flow through the shunting resistors 32, 34. As a result,'losses will 45 arise which also will tend to cause the oscillation generator to return to a frequency giving minimum. loss, namely, it will cause the generating system to tend to return to the desired frequency which causes the crystal to act as an effective 50 short circuit. If the change produced in the circuits of the oscillation generating system is too great with accompanying larger losses, the entire system will cease oscillating. Hence, it follows that an operator or any other person cannot put the frequency substantially off the normal operating frequency by incorrect adjustment.

A further advantage of the oscillation generator shown resides in the fact that it will produce a high power output at substantially constant frequency.

In the system shown in Figure 2, switch 200 is first closed, short circuiting the crystal 26 and its series connected electrode capacity tuning coil 28. The grid tuned circuit consisting of variable condenser l6 and coil I8, and the plate circuit consisting of condenser 8 and coil H) are then tuned so that oscillation generation takes place at a desired operating frequency. The feed-back may be adjusted by simply tuning the grid and plate circuits or, if desired, in the alternative or in addition, a screen grid 202 may be provided to substantially eliminate inter-electrode feed-back and an external variable feed-back condenser 204 be provided for additional regenerative control. Should the screen grid 202 be provided, it should be by-passed to ground by suitable by-passing condenser 2| and it may be supplied with suitable operating voltage through the action of voltage dropping resistor 208.

In any event, with the system oscillating, and as before stated, the crystal 26 and coil 28 short circuited by the action of switch 200, the switch 200 is thenopened. The frequency should then be brought back to the desired operating frequency corresponding to the frequency of the frequency controlling circuit or crystal 26 by adjusting the coil 28 serving to tune out the electrode to crystal capacity of the crystal holder for crystal 26. This may be facilitated by the provision of one or more adjustable crystal electrodes, such as crystal electrode 206.

As stated in connection with Figure 1, when this last adjustment is made, the crystal system con sisting of coil 28, the crystal 26 and its holder acts as an effective short circuit. In other words, it acts effectively as the switch 200 in its closed position. Should the system now be tuned away from the crystal frequency, the crystal will offer a high reactance to the new frequency, causing losses in resistance 34 to such an extent that the system will stop oscillating. On the other hand, if the change in frequency is not great, the oscillator will tend to operate at minimum loss, namely, at that frequency for which the crystal is an effective short circuit or, in short, at the desired operating frequency rather than at some new frequency causing losses.

Obviously, many changes may be made within the scope of my present invention. For example, inductive feed-back may be used, in which case coils l and I8 and I0 and 20 may be coupled together. Also, for example, the present invention may be incorporated in an electron coupled type of generator in which the present plates or anodes would be replaced by grids of a tube and the output taken from the normal plates of the tubes in the manner shown, for example, in Harry Tunick Patent No. 2,044,137, granted June 16, 1936.

Having thus described my invention, what I claim is:

1. Anoscillation generator comprising a pair of tubes each having an anode, a cathode and a control grid, a circuit having inductance and capacity connected effectively in phase opposition across said anodes, condensers cross-connecting said anodes and control grids for establishing feed-back from said anodes to said grids, a parallel tuned circuit having a variable condenser, and a pair of inductance coils connected across said control grids, a crystal having negligible impedance at the desired operating frequency connected in serieswith said parallel tuned circuit, coils connected in series with said crystal for tuning out crystal electrode capacity, anda resistance circuit connected in shunt to said crystal and the last mentioned coils. I

2. An oscillation generator comprising a pair of electron discharge tubes each having a cathode, an anode and a control grid, aparallel resonant circuit interconnecting their anodes, a second parallel resonant circuit interconnecting their control grids, a feed back arrangement comprising two capacitively coupled circuits, one connected between the anode of the first tube and the control grid of the second tube, the other circuit being connected between the anode of the second tube and the control gride of .the first tube, the inductive leg of said secondlparallel tuned circuit including a piezo-electric deviceshunted by a pair of resistors, and a connection common to the two resistors and to the two cath0des.'

3., A generator according to claim 2 and having inductive means in said second parallel resonant circuit for neutralizing theelectrode capacitance of said piezo-electric device.

CLARENCE 'I-IANSELL.

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