US1984424A - Variably tuned piezo-electric resonator - Google Patents

Description

D66. M OSNQS J VARIABLY TUNED PIEZO ELECTRIC RESONATOR Filed May 4, 1929 "nil? INVENTOR M OSN 5 ATTORNEY Patented Dec. 18, 1934 3 UNITED STATES PATENT OFFICE VARIABLY TUNED PIEZO-ELECTRIC RESONATOR Germany Application May 1929,.Serial No. 360,395 In Germany June 23, 1928 7 Claims. (01. 250-36) It is known in the prior art that the wavelength of a circuit controlled by a crystal may be slightly altered by variation of a capacity connected in series with the crystal.

was only As has been shown by further tests this method was attended with a rather marked decrease in the useful current when the wave-length was reduced.

It is therefore an object of the present invention to provide a crystal controlled circuit which permits certain variations in wave-length using 1 crystals each of which has a predetermined natural period.

Now, according to the present invention a considerably greater change in the wave-length is attainable if, say, two crystals are connected instead of only one according to former practice, and if one or the other crystal is cut in circuit alternately and then the two'crystals are connected in parallel.

The manner in which the present invention is carried out will be more clearly understood from the following description taken in connection with the accompanying drawing, in which:

i Fig. 1 shows one arrangement for varying the wave-length of a crystal controlled circuit;

Fig. 2 shows an arrangement in which various wave-lengths may be had with one or two crystals in the circuit; and

Fig. 3 shows a'modification.

In Figure 1 is shown an oscillation generator in which the frequency of the oscillations generated is determined by a circuit including a crystal K in series with a tuning capacity Ck. The wave length generated in the thermionic tube to a great extent is determined by the nature of the crystal K. This frequency, however, may be varied over limited range by means of the tuning capacity Ck.

In Figure 2 two crystals, K and K1, are arranged to be connected alternately or simultaneously in circuit by means of switches a and a1 with tuning capacities Ck as shown. Furthermore, these crystals K and K1, and/or their However, this method allows of insuring only tuning capacities, may be connected in series with each other and in the resonance circuit with switching means not shown.

Experience has shown that even when both crystals have the same, or nearly the same, nat- 5 ural period, the addition of the second crystal insures a considerable variation in wave-length. When the two crystals are connected in parallel a new frequency, differing from the individual crystal frequencies, is produced. This 10 new frequency is not the algebraic sum of the individual crystal frequencies. When the two crystals are connected in parallel each tends to resonate at its particular frequency, but each pulls the other away from its normal frequency 1 so that a new distinct frequency is produced bythe two crystals, which appear to be entrained. This new frequency can be varied over a predetermined frequency range by the capacities. 20

If the circuit of one or both crystals is k1 is untuned in relation to the natural period of the latter, for instance, by the aid of variable capacities Ck (see Fig. 2), then, as shown by practical experiments a relative frequency 25 change of about 5/10000 or even slightly more is' obtainable by the opening and closing of switch a.

Another advantage is that the useful current decreases far less when a frequency change is insured by means of two crystals as shown in Fig. 2 than when only one crystal is employed as in Fig. 1.

The crystals could also be connected in series relation to each other, and then again a different wave-length is obtained.

The method here disclosed offers a still further advantage; for instance, if a transmitter is required to send out various waves, a separate crystal has heretofore been required for each wave, so that for n waves, 11 crystals were needed. According to this invention, however, even with only two crystals differing slightly in their natural period, at least four waves can be used at will, to wit:

1. When the crystal K only is connected into the frequency determining circuit, including the tuning capacity Ck, the frequency of the oscillations generated will be determined by K and Ck.

2. When the crystal K1 only is connected into the frequency determining circuit, including the tuning capacity Ck, a different frequency, assuming the values of K and K1 are diiferent, Will be generated. 55

with the tuning condenser O in the coupling means (not shown), again it will be obvious to anyone familiar with the-,radio-art .that;the

natural frequency of the frequency determined circuit will be different than in any of the prior cases.

If three crystals areprovidedin lieu of, two,

then 17 different wave-lengths are obtainable as can be seen from a simple calculation, even without the use of capacities JCk.

The number of wave-lengths obtainable grows very rapidly with the number of the crystals since a great number of group arrangements or combinations ofthe crystalsare,feasiblegquite apart from seriesandparallelconnection. For instance, with-four crystalslOO-wavesare obtained.

,But if the crystal circuits are ,cletuned in relation toone another by-diiferent capacities (as indicated, forinstanca-in Fig. 2 by capacities Ck),,the number of ensuingfrequencies can beconsiderably increased. The inter-electrode capacity of the tube,may-be partially neutralized ,by the condenser Cu connected as shown.

Series connection of the crystals offers the ;particular advantage that the tuning Of the circuit turns ,out to be muchsharper, afact which .is especially valuable inreceiver tubes. One exemplification for radio frequency reception is shown inuEig. .3. Between antenna A and the grid circuit of a radio frequency amplifier 1; there is inserted ,an intermediate circuit tuned by crystals is. In broadcast :re-

-; cepti on, whenever the local station :disturbs dong-distance reception, the influence of the local station can be very eifectively eliminated .by means of suitable choice of the crystals. Foreach long-distance station a distinct crystal combination is ,-,used; for example, for the .Cologne broadcast station a certain crystal or crystal combination, for the Paris wave another.

crystal or crystal combination, ,etc. That a great number of frequencies can'be obtained with this arrangement may be seen from the following: Assumepthat the .crystals K of Figure 3 are all of individual characteristic and, further, that the crystals K of Figure 3 are numbered from 1 to'6 in sequence fromthe top of the page to the bottom. Crystals 1, 2 and 3 w ll be in the upper group and crystals 4, 5

and 6 will be in the lower group. Merely by manipulating the switches shown combinations of the crystalsas follows may be placed in series circuitLA; 1, 5; 1, 6; 2, 4; 2, 5; 2, 6; 3, 4; 3, 5; 3, 6;' 1, 2, 4; 1, 2, 5; 1, 2, 6; 1, 2, 3, 4; 1, 2, 3, 5; 1, 2 3, 6 1, 4, 5; 2, 4, 5; 3, 4, 5; etc. Each combination will cause the circuit to be normally resonant at a different frequency. This is so obvious that it is thought needless to go any further into the reasons why this is so.

The natural frequencies of the crystals need notbe of any definite relative values. All that is imperative is that the circuit including the crystal combinations or groups, with the aid of the tuning means, resonate at the desired frequency.

Having thus described the invention, I claim:

1. A radio frequency oscillator adapted to be variably tuned from one value of wave-length to another, in combination with a piezo-electric control device having a plurality of piezo-electriccrystalelements, and switching means selectively to connect said elements in different combinations, said device being adapted to control -said oscillator to hold substantially constant the frequency of oscillations produced at various wave-lengths of said oscillations, the number of crystal elements in the device being less than thenumber-ofwave-lengths to which the oscil- ,lator mayibe setfor operation under control of the deviceandthe control frequency of said combination of control devices being greater lthanranybeatanote capable of being produced by the difference frequencies from said piezoelectric elements.

2. In combination an oscillation generator, a plurality of "piezo-electric control devices connected thereto, each of said devices having a natural frequencyof vibration, and switching means selectively to disconnect any one or: more "of said-devices, leaving at least two of said de-:

vices connected to said generator, and circuit controllingimeans for controlling the frequency of oscillations produced'by said generator at a value substantially constant and different from the natural frequency of any one of said connected crystals by an amount less than the beat frequencies between said connected crystals.

3. In combination an oscillation generator, a

plurality of piezo-electric control devices connected thereto, each ofsaid devices having a natural frequency of vibration, "a variable impedanceconnected to each of said devices, and

means selectively to disconnect any one or more of said devices, leaving at least two of said deyices connected tosaid generator, said variable.

impedance means being'aclapted to control the frequency :of oscillations produced by said generator at aivalue substantially constant and different from the natural frequency of any one of said connected crystals and from the algebraic "sumof the natural frequencies of the connected crystals.

4. In combination,.a tunable circuit, -a plurality oil-mechanical vibrating devices having different natural periods of vibration,

and switching mechanisms for combining said devicestoproduce oscillations of a frequency dif- ,fering fromthat represented by the sum or difference of the individual natural periodsof vibration of said devices.

5. In combination, a tunable circuit, twopiezo-electric crystal resonators associated with said circuit, each-of said crystal resonators having a natural period of vibration, switching devices for combining said two piezo-electric resonators to produce oscillations of a frequency which differs from the natural period of vibration of anyone of said two resonators and from the algebraic sum of the natural periods of said resonators, and variable frequency controlling means for varying the frequency of the said oscillations over a predetermined desired frequency range.

6. In combination, a tunable circuit, a plurality of piezo-electric crystal resonators having different natural periods of vibration, manually operable switching devices for connecting groups of said crystal resonators in said circuit to produce oscillations of a frequency which differs from the natural period of any' one of said resonators, and capacitive elements for controlling the frequency of said oscillations to obtain a predetermined frequency which differs from that represented by the sum or difference of the individual natural period of said resonators.

7. In combination, a tunable circuit, a plurality of piezo-electric crystal resonators associated with said circuit, each of said resonators taken alone having a natural period of vibration, switching means to selectively connect any one of said resonators or combinations of one or more of said resonators to said circuit for producing a period of vibration different from the natural period of any one of said resonators included in the combination, said piezo-electric crystal resonators being adapted to control said tunable circuit at a frequency which differs from that represented by the sum or difference of the individual natural periods of said resonators.

MENDEL OSNOS.

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