US2017712A

US2017712A - Frequency determining means

Info

Publication number: US2017712A
Application number: US717224A
Authority: US
Inventors: Reginald L Downey
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1934-03-24
Filing date: 1934-03-24
Publication date: 1935-10-15
Anticipated expiration: 1952-10-15

Description

@(Zfi. 15, 1935. R, DOWNEY FREQUENCY DETERMINING MEANS Filed March 24, 1934 Fig.1.

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1 IIMIIMA Inventor:

uw m w m m m Lmmm M K MW i H win R UlTED STATES PATENT OFFICE FREQUENCY DETERMINING MEANS Reginald L. Downey, Scotia, N. Y., assignor'to General Electric Company, a corporation of New York Application March 24, 1934, Serial No. 717,224

Claims.

My invention relates to frequency determining means and it has for one ofits objects to provide an extremely economical means for measuring radio frequencies with a desired radio range.

5 A further object of my invention is to provide such means involving a minimum number of tubes and which may be incorporated in a minimum of space thereby to increase its applicability to use on aircraft.

A further object of my invention is to provide such means capable of greater stability of operation and greater accuracy than has been possible 'in the past and whereby the oscillation generators involved are protected against variations in the circuits of the system other than those of the particular oscillation generator.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents an embodiment of my invention and Fig. 2 represents a modification thereof.

Referring to the drawing, I have shown therein a frequency determining device in accordance with my invention, and which employs a plurality of electron discharge devices I, 2, and 3. Discharge devices I and 2 are of the multi-grid type and operate both as oscillation generators and as amplifiers while the discharge device 3 is a threeelement electron discharge device which serves as an audio amplifier.

All of these discharge devices are arranged to be energized from a suitable source of energy 4 the positive terminal of which is connected through resistance 5 to the anode of discharge device l through resistance 1 and inductance 8, which is shunted by a resistance 9, to the anode of discharge device 2, and through the primary winding of an audio transformer I!) to the anode of discharge device 3. This source of potential 4 also supplies operating potential to screen grids I and I2 in discharge devices I and 2 through the resistances I3 and M respectively. The cathodes of all of the discharge devices are connected to the negative side of the source of potential through bias resistances l5, l6 and I1, respectively, each of these resistances being shunted by a suitable radio frequency bypass capacitor l 8. The heating elements for the cathodes of each of the discharge devices are also energized from a portion of the source of potential 4, the circuit for these heating elements extending through contacts on jacks l9 and 20 connected to the secondary winding of the transformer ID. A plug 2|, to which is connected a pair of headphones 22, 5 cooperates with the jacks l9 and 20 and when inserted therein closes contacts 23 and 24 thereby energizing the heating elements of all of the tubes through an energizing circuit including a portion of source 4. 10

The discharge device lhas its two grids nearest to the cathode connected to operate as a piezo electric oscillation generator, the grid 25 nearest the cathode being connected to the cathode through resistance 26 and the grid bias resistance 15 I5, and the grid 21 next removed from the cathode being connected to the positive terminal of the source of anode potential 4 through a fixed tuning inductance 2'? and a voltage dropping resistance 28. 20

The resistance 26 is arranged to be shunted by any one of a plurality of piezo electric crystals 29 dependent upon the position of a movable contact 3D. The tuning inductance 21 has a fixed natural period outside of the frequency range 25 of the crystals 29 so that by moving the contact 30 into engagement with an electrode of any of the cells of the crystals 29 a frequency determined by the particular crystal is produced. The frequencies preferably are spaced apart in the de- 30 sired frequency range and differ from each other by approximately I0 kilocycles or more.

Discharge device 2 is likewise adapted by means of its two

grids

36 and 31 nearest the cathode to produce oscillations. These oscillations are gen- 35 erated in a circuit comprising a variable condenser 3| and either of two

inductances

32 and 33 dependent upon the position of

switches

34 and 35, this circuit being connected between the two

inner grids

36 and 31 of the discharge device 2. The 4.0 respective midpoints of the

inductances

32 and 33 are connected through a resistance 38 to the positive side of the source of anode potential whereby high positive potential is supplied to the grid 31. The inner grid 36 is isolated from this source 45 of unidirectional potential by grid condenser 39 and is connected to the negative side of the source of potential through a grid leak resistance 40. Thus these grids 36 and 3'! are connected in a manner conventional to the grid and anode of 50 three element electron discharge devices arranged to produce oscillations.

The oscillations the frequency of which is to be determined are received in a receiving circuit, not shown, which may be a simple antenna, con- 55 nected to the grid 4| of discharge device through a coupling condenser 42. This grid receives its bias voltage from resistance |5 to which it is connected through a radio frequency impedance 43 which may be a resistance or choke coil. The anode of the discharge device I is connected to a grid 44 in discharge device 2 corresponding to the grid 4| of discharge device I. These grids 4| and 44 are spaced nearer the anode of the respective discharge devices than the oscillating grids of the corresponding devices and are shielded both from the anode and from the oscillating grids by means of the

shield grids

45 and 46 respectively. The anode of the discharge device 2 connected through the radio frequency impedance comprising the combination of choke coil 8 and resistance 9, and coupling condenser 41 to the grid of audio frequency amplifier 3.

The operation of my device may now be explained.

Let us assume that the device is used, for example, to check the frequency of an associated transmitter, as, for example, in an aircraft installation. The oscillations from the associated transmitter are received through condenser 42. Let us assume that the associated transmitter should produce a frequency corresponding to the natural frequency of one of the crystals 29. The contact 30 is placed upon the respective crystal and the plug 2| is inserted into one of the jacks I9 or 20. Oscillations having the frequency of the piezo electric crystal are then produced by the crystal and supplied to the output circuit of the discharge device I. Similarly oscillations from the associated transmitter received through condenser 42 and amplified in discharge device I are supplied to the output circuit, both of these oscillations being supplied to the grid 44 of discharge device 2 through condenser 49. The discharge device 2 acts as a grid leak detector of these oscillations whereby if the frequency of the associated transmitter be different from that of the corresponding crystal 29 a beat note is produced in the output circuit of discharge device 2, which is amplified in discharge device 3 and heard in the headphones 22. By means of the tuning device of the associated transmitter the operator may adjust the frequency thereof, by listening to the headphones 22, to produce a zero beat with the known fixed frequency produced by discharge device I under control of the respective crystal 29.

Now let us assume that it is desirable to produce a frequency by the associated transmitter which differs from that produced by any of the crystals 29. Contact 30 is moved to engage the electrode of the crystal having a natural frequency nearest the frequency to be produced by the associated transmitter.

Switches

34 and 35 are then operated to the position to connect in circuit the

appropriate inductance

32 or 33 and the condenser 3| is adjusted to cause the discharge device 2 to produce a frequency equal to the frequency of the piezo electric crystal then included in circuit. This adjustment may be effected by the zero beat method, the operator listening to the headphones 22 and adjusting the condenser 3| until the zero beat position is found. The operator may then refer to his chart showing the dial position frequency characteristic of the oscillator 2 and note any variation between the dial setting of condenser 3| and that denoted by his dial position-frequency characteristic corresponding to the frequency of the piezo-electric crystal. He then adjusts the condenser 3| to produce the frequency which it is desired to produce by the associated transmitter taking into consideration the correction thus observed. He is then in readiness to adjust the frequency of the associated transmitter which he may do simply by adjusting the tuning device on the associated transmitter While listening to the headphones 22 until a zero beat position is found between the oscillations produced by the transmitter and those produced in the

circuit

32, 33.

During this latter operation the contact 30 may be moved off from any of the crystal cells thereby to avoid the production in the system of oscillations of the frequency of any of the crystals. This operation, however, is not necessary Where the frequency produced by the piezo-electric crystal differs from that for which the condenser 3| is adjusted by an amount so great that no beat notes are produced which interfere with the detection of the zero beat position between the associated transmitter and the oscillations of the circuit 3|, 32, 33.

In this way the associated transmitter may be adjusted to any frequency within the desired range and its frequency checked with the accuracy determined by the piezo-electric crystal.

While in the above description I have mentioned the discharge device 2 as acting as the detector of oscillations received from the discharge device I, it will be understood that with the connections shown the discharge device I 1 may likewise operate as a detector producing a beat note between the oscillations produced by the crystal and those received through condenser 42. Since a capacitance resistance coupling is employed between the anode of discharge device In accordance with my invention either of the discharge devices and 2 may be employed as a source of oscillations to be used for purposes other than those herein previously indicated. This is indicated by the fact that the anode of discharge device 2 is arranged to be connected through an output condenser 48 to any suitable high frequency utilization circuit. In the event that it is desired to produce a frequency corresponding to the natural frequency of one of the crystals 29 the

switches

34 and 35 may be moved to their intermediate position where no oscillations are produced in the circuit 3|, 32, 33 or condenser 3| may be moved to a position when the frequency produced is not objectionable in the output. responding crystal are thus supplied to the grid 44 of discharge device 2 in which they are amplified and supplied through the coupling condenser 48 to the desired utilization circuit. If the frequency to be produced be one which differs from that produced by the piezo-electric crystal the contact 30 may be moved off from any crystal cell and the condenser 3| adjusted to the desired

frequency switches

34 and 35 of course being in one of their two alternative positions. Of course the accuracy of this frequency adjustment may be determined by the zero beat method utilizing the crystals 29 and headphones 22 as previously described.

The two jacks I9 and 20 are provided for pur- Oscillations generated by the corpose of adjusting the intensity of oscillations received in the headphones 22. If the plug 2| be inserted in the jack ii! the headphones are connected across the entire secondary winding of transformer Iii, whereas if it be inserted in the jack 2i] the headphones are connected across only a portion of this secondary winding. In this way the impedance of the output is matched with that of the particular headphones employed thereby to produce a maximum transfer of energy to the headphones.

It will be observed that the circuits of both of the oscillation generators are shielded by grids and 36 from each other and from other components of the circuit. These shield grids extend on both sides of the respective control grids 4| and 44. In this way improved frequency stability is obtained, the frequency of neither generator being affected by the condition of the other generator, or by the condition of the external circuits such as the input circuit connected to condenser 42, or the output circuit connected to condenser 48. Thus impedance variations and undesired radio-frequency pickup in these elements of the system do not effect the frequency of oscillations produced.

It frequently occurs in producing a beat note between the crystal controlled oscillations and oscillations produced by tube 2 that it is desired to use a harmonic of a crystal frequency. These harmonic currents are weak as generated in the crystal oscillator. It has been found that in my system such harmonics are amplified in tube l to an energy level comparable with the oscillations produced by tube 2 whereby these harmonic oscillations may be utilized for the production of beat notes quite as efficiently as the natural frequencies of the crystals.

In Fig. 2 I have illustrated a modification of my invention which differs from Fig. 1 only in that grids 3t and 31 of tube 2 are connected differently to produce oscillations. In this figure grid 3i is connected to ground through condenser 50 and is operated at ground radio frequency potential. This grid is supplied with positive operating potential from battery 4 through resistance 38 as indicated. The cathode is connected to ground through switch 34, left portion of one or the other of inductances 32' and 33' and bias resistance l6 whereby it is biased above ground potential. Grid 36 is biased negatively with respect to the cathode by means of grid leak till and grid condenser 39 as in Fig. l. The tuned circuit of the oscillator comprises the Variable condenser 3| and either of inductances 32 and 33' which may be selectively connected in circuit by operation of switches 34' and 35' either to the right or left.

It will now be understood from the description given that my system is capable of widely varying application both for the measurement and production of radio frequencies. It essentially incorporates but two discharge devices, the discharge device 3 being merely an amplifier which may be omitted if desired. The device is especially well adapted for use on aircraft for determination of the frequencies of the transmitters so employed since in its physical construction it is extremely light and may occupy a minimum of space.

While I have shown a particular embodiment of my invention it will of course be understood that I do not wish to be limited thereto since diiferent modifications both in the circuit arrangement and instrumentalities employed may be made and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a pair of electron discharge devices, each of said discharge devices having circuit means connected therewith to generate oscillations, piezo electric means to control the fre- 10 quency of oscillations generated by one of said means, the oscillations generated by the other means being variable over a range including the frequency of said piezo electric means, means whereby a beat note between oscillations gener- 15 ated in said two circuit means is produced in the anode circuit of one of said discharge devices, and means in said discharge devices to prevent variation of frequency of oscillations generated by either of said circuit means from being affected by the condition of the other circuit means.

2. In combination, a pair of electron discharge devices, each of said discharge devices having circuit means connected therewith to generate oscillations, piezo electric means to control the fre quency of oscillations generated by one of said means, the oscillations generated by the other means being variable over a range including the frequency of said piezo electric means, a radio frequency anode circuit for one of said discharge devices, a radio frequency coupling between said devices and means in said discharge devices to shield both of said circuit means from the other circuit means and from said radio frequency anode circuit.

3. In combination, a pair of electron discharge devices, each of said devices having an anode, a cathode and a plurality of grids, oscillation generating means including a pair of grids in each device, said oscillation generating means including the grids of one device comprising a piezo electric crystal, and the oscillation generating means including the grids of the other discharge device comprising means to vary the frequency of oscillations produced over a range including the frequency produced by said crystal, means to supply radio frequency oscillations to an additional grid in one of said devices, a coupling between the anode of said one device and an additional grid in the other device, and an audio frequency output circuit connected to the anode of said other device whereby oscillations either generated by, or received in, said one'discharge device are supplied to the other discharge device and a beat note between said oscillations and oscillations produced in said other device appears in said output circuit.

4. In combination, a pair of electron discharge devices, each of said devices having an anode, a cathode and at least three grids, means including two of said grids nearest the cathode of each device to produce oscillations therein, said means including said grids of one device including a piezo electric device for controlling the frequency of oscillations produced, and said means including said grids of said other device comprising means for adjusting the frequency over a range including a frequency controlled by said piezo electric crystal, a receiving circuit connected to a grid of said first device more remote from the cathode than said two grids, a coupling between the anode of said first device and a grid of said second device more remote from the cathode than said two grids, and an audio output circuit connected to the anode of said first device, whereby oscillations received in said receiving circuit are amplified in said first device and supplied to said second device, and a beat note may be produced between said oscillations and oscillations produced by either of said means, said beat note appearing in said output circuit.

5. In combination, a pair of multigrid discharge devices, means individual to each discharge device utilizing the two grids nearest the cathode of the respective discharge device to produce oscillations, a radio frequency input connected to a grid in one of said devices more remote from the respective cathode than said two grids, a coupling between the anode of said one device and a. grid of the other device more remote from the respective cathode than said two grids, an output circuit connected to the anode of said other device, and shielding means in each device whereby said more remote grids are shielded from said first mentioned two grids in the respective discharge device and from the respective anode.

REGINALD L. DOWNEY.