US2456421A - Dual crystal unit - Google Patents

Description

Dec. 14, 194s.v R J, JAHRUNG 2,456,421

DUAL CRYSTAL UN IT Filed March 15, 1948 (mnu.

UNIT

gmc/wm PoERT J: Mp4/N6 AToRNEY 2 sneets-shet 2 Patented Dec. 14, 1948 DUAL GRYSTMI- Robert-Jr. .Iahrling .IamaeaN; Ywassg-,norr to Premier Crystal. Laboratnxieg. Incorporated,

New York,.N. Y.

Applwienmmn. 15, lamentiamo. intesa.y

(ci. 1v1-327.),

7.01aims,

'1-'1 Thisfirrventimrrelates. opiezoL-electric crystal assemblies, .and-moreparticularly Vto a crystal unit adapted* .tcrr provide y az stable low f when connected s to a'. suitable oscillator circuit..

A main; obiecti of 'f the:V invention isA` tof-provide anovel.: and; improved-crystal iinitiof*` theY dual f ty-,pe

whiehisr especially adaptedfor'nse-with dual oscillatonsY totproducefa; stable .beat frequency, such as: aniaudio frequency, saidunit having self-cont'ainedffmeanst fior.v adjusting they `resul-tant beat frequemicyrby adjustingfthe frequency-ot one crystmL. f

1`..fm:t1"1er.r object of. the a invention is tty-provide am;I imp1'erred?r dual. crystal assembly embodyingmeans: for yadustirxgv the beat frequency obtainahlenfrmn oscillators controlled byfthe respective crystals when said oscillators are heterodyned; the: ass errzbly.l being; very simple in construction, compact, in .size; and `relatively inexpensive to manufacture.

Astilifiurther object ofy the invention is to pro-- vida arr improvedi dual.' crystal. assembly for use with; heterodyning; oscillators to prow-ide a` stable beat. frequency,y sncl'r audio frequency,v the assembly being?r readilyadjnstable.- so-that an eX-- act beat frequency value may be @tained-.when the unit is employed as above-deseribed,-the-ad justing. meansfbeing-vaccessible from outside the unit, the unit. beingveryrugged in` construction andinvolving, only asmallniimber. of parts.

lurther objects and advantages of. the inyen.- tion-wilt.become-apparent 'from the following description. and: claims, and. from the. accompanying drawings, wherein: f

Eigure 1. is. a transverseyertical. cross-sectional View` takenthrougha dual.I crystalnnit vconstruct.- ed in. accordance with the presentinvention, said View being. takenoxiline` I-l of .Figure 2..

Figure 2: is a horizontal cross-sectional, View. taken.y throngh.- the unit oirigure. l. onthe lin theref.

Figure 4% is-.a.,s.che-matic.-diagram illustrating-arst method; of connectingthecomponent. ele` ments of.thecrystalsy assembly ofiliigure; 1..

Figure. 5- isf a schematic diagran-r.ilhistratimzc,` a, second, method of ccnneeting-v the componenty elements of the 1 crystal assembly of- Elgure.

Fig-uref Ghisa perspective-view.' of thegronndA plate employed in the crystal inrity of. Figure-11:. show-ing; additionaly elements vofthe, assembly aecured'theretor f f Figure `71: is r an.- enlarged fragmentary cross-sec.- tionaLdeiail-view. takerri line-'l--Ji-of Eigurfea.

vllig-iir-e- 8 isk ay block diagram illustratingv the mammaire-.which the. crystal uni-t of Figure-'Lis employed.- Withrhetercdyni-ng oscillators. to., pro-- duce-1y aidesired stable. beatirequency.,

Rotating, to.-y the drawings, the housing of, the crystal: .mm1-is designated generally.r at Il. and comprisesa.- base-.plate- I?. ot siiiitable;ifnsaulating matesiaanda cover member I-3, also,I of insulating material,.w-lch securedtothe base plataby screws I-,ll'-whiclr nass upwardly through-.baseplate t2 antil `aretlzireaded,into. the edge. portions., oi the.- correr'mernilaer: I3. Designated. at Ii` is a. vertical. metal plate.- fitting closely, b etxiveen.v the` opposite inside wall-,f surfaces ofcover; memberI I.; plata. Ifbeng formed. with a. horizontal `mbt-.- tom ,flange I6.. Designated at Il; is a .pronti havingatlireadedshank portioni which passesunwardlgythroughfbase plate I2! and. through. flange It. Prong, L1. isiormedwith a hexagonalcoliar I9 which, bears onthe, bottom surface of. .basev plate-l 2: and has-threaded; on. the shank'. portion Ieanut. 2,0..which,bears on flange IB, whereby nlate. I5..-.is-tightly secured to platev l2..and.-prong I1 affords-.ana electrical connection. thereto.

Designated. at,` 2JY a variable. trimmer con.- denser.- ai, wel]-knownconstruction,y such. as Cen.- tralala part 823-AN-madeby Centralabf aDivison oi Globe-Union. Inc., Milwaukee... Wisconsin, said condenser being characterized by havinga. `hex-- agonal stud. 22. projecting from itscentral. portion., inwhichisthreaded. the. trimmer adjusting screwA 2.1 Whiclrmay berot-ated by a screw driver towadjust. thezcapacitanoeof. the. condenser. Proiectingjroro thehody of,A the. trimmer. 2 I. on opposite. of. the-stud. 22 are square. metal, studs. Z4, 2A', rireteito. the body ofthe trimmer, said studs 24,.. 24.. being. tapped. to receive fastening sereine?. VDesignated; atl, and 2li. are vertioaldn: sulatingbars-oiu substantial.. thickness .and similar. in-.shape` Bars 7.5.. and-,2.6 are formedat their lower ends with respective opposingA arms,"

2a .at1 theirY intermediate portions with respecopposina arms 29 and 30.-. Passing through arms. la and.. imv and. through vertical.. plate. Il

' are fastening screws 3 I, 3I which threadedlyf. en,-

gage the trimmed. studs 24,. 24, and. secureA the-respec-.tivebars, 25,. 26 to the.. plate member I5, on one. side. thereof. andthe, trimmer condenser 21., toy saidfplate memberonthe othersidethereof. The enten-.surfaces ofthe bars..25. and. 2E are. substanr tallyilushwiththe-edges-.o plate member. l5 ao thatsaidouter surfacesaarealso closely fittedlin.-

side .wanner-.member t3.

.Rlatemember. I5- aformed. with. a.; circular:

stud being therefore positioned between the inwardly extending arms 29 and 30 of the bars 25 and 26. Threaded into the wall of cover member I3 in axial alignment with trimmer screw 23 is a removable plug 33. When plug 33 is unscrewed from the wall of cover member I3, a screw driver may be inserted into the unit to engage the trim.. mer screw 23 for adjusting the capacitance of trimmer 2|.

Arms 29 and 30 define with the upper portions of bars 25 and 26, plate member l5, and the top wall of cover member I3 a rectangular cavity. Positioned in the cavity adjacent plate member I is a first crystal plate 34. Positioned adjacent the side edges of crystal plate 34 are vertical spacer bars 35, 35 of insulating material, such as glass, slightly greater in thickness than crystal plate 34. Bearing on the spacer bars is a metal electrode 36 which closely fits into the cavity, said spacer bars providing a small air gap between the electrode 36 and the crystal plate 34. Secured to the bars and 26 is a metal strap member 31 which bridges the cavity in which the crystal plate 34 and the electrode 36 are contained. A coiled spring 38 is positioned between electrode 36 and strap member 31, whereby electrode 36 is firmly held in abutment with the spacer bars 35.

Arms 21 and 28 define with arms 29 and 30, the lower portions of bars 25 and 26, and plate member I5, a second rectangular cavity. Positioned in said second cavity adjacent plate member I5 is a second crystal plate 39. Positioned adjacent the side edges of crystal plate 39 are additional vertical insulating spacer bars 35, slightly greater in thickness than plate 39. An electrode 46 is fitted in said second cavity and bears on the spacer bars 35, 35 therein. A second strap member 4I is secured to bars 25 and 26, which bridges said second cavity. A coiled spring 42 is positioned between electrode 40 and strap member 4I, whereby electrode 40 is rmly held in abutment with the spacer bars 35, 35 in the second cavity.

Designated at 43 and 44 are additional prong members secured to base member I2 parallel to prong member I1, said prong members having hexagonal collars shown respectively at and 46 and threaded Shanks passing through base member I2, on which respective nuts 41 and 46 are threaded.

The crystal plates 34 and 39 are matched in frequency and have identical temperature-frequency characteristics. The assembly may be wired in either the manner shown in Figure 4 or the manner shown in Figure 5. In Figure 4, crystal electrode 36 is connected by a wire 49 to prong 43 and crystal electrode 40 is connected by a wire 50 to prong 44. The trimmer condenser 2| is connected in parallel with crystal 34, one terminal of the condenser being connected to plate member I5 and the other terminal thereof being connected to the prong 43.

In Figure 5 the trimmer condenser 2| is connected in `series with crystal 34 instead of being connected in parallel therewith as shown in Figure 4.

Figure 8 discloses the manner in which the unit is connected to an external circuit in order to provide a desired audio frequency output signal. The circuit comprises a first oscillator 5| and a similar second oscillator 52. The prongs I1 and 43 are connected to the input terminals of oscillator 5| and the prongs I1 and 44 are connected to the input terminals of oscillator 52. The output terminals of the oscillators are connected to the input circuit of a mixer stage 53 wherein the frequencies of oscillators 5| and 52 are heterodyned, providing a low frequency beat signa] at the output terminals of said mixer stage. By adjusting the trimmer condenser 2| in the manner above described, the beat signal may be made to have any desired audio frequency. Since the crystals have identical frequency-temperature characteristics, the derived beat frequency will remain constant in value over a considerable range of temperatures.

Heretofore where crystal controlled oscillators have been employed to provide a stable beat frequency, the crystals controlling the respective beating oscillators were physically in different environments, and although the crystals may have had identical temperature-frequency character istics, variation in the respective temperatures of the crystals has not been necessarily the same for both crystals. This has produced a substantial degree of instability of the beat frequency thus derived, especially where said beat frequency was of a low audio value. Where it was necessary to maintain stability of the audio frequency within close limits, the above described heterodyne method has been unsuccessful because even a few degrees variation in temperature between the crystals has resulted in many cycles of difference in the derived audio beat frequency. In the unit of the present invention, both crystals are in close physical contact with the metal ground plate I5, and although the temperature of said plate may vary, there is no difference in the temperature of the crystals. Therefore, once the beat frequency has been established by the adjustment of the trimmer condenser 2 I, the beat frequency will remain constant regardless of external temperature conditions.

While a specic embodiment of a dual crystal assembly for use in beat frequency oscillator circuits has been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims What is claimed is:

1. A dual crystal holder comprising a base, an upstanding metal plate member secured to said base, a pair of insulating bars secured to opposing marginal portions of said plate member on one side thereof, said bars being formed with pairs of opposing projections defining with respect to said plate member a pair of crystal-receiving cavities, said plate member being formed between one pair of said opposing projections with an opening, and an adjustable impedance secured to the opposite side of said plate member and having an adjusting element aligned with said opening.

2. A dual crystal holder comprising a base, an upstanding metal plate member secured to said base, a pair of insulating bars secured to the side marginal portions of said plate member at one face thereof, said bars being formed with inwardly projecting opposing arms defining an up.. per and a lower crystal cavity, said plate member being formed between one set of opposing arms with an opening, and an adjustable impedance secured to the opposite face of said plate member and having an adjusting element aligned with said opening.

3. A dual crystal holder comprising a base, an upstanding metal plate member secured to said base, a pair of insulating bars secured to the side marginal portions of said plate member at one face thereof, said bars being formed with inwardly projecting opposing arms defining an upper and a lower crystal-receiving cavity, said `plate member being formed between the opposing arms intermediate the cavities with an opening, and an adjustable condenser secured to the opposite face of said plate member and having an adjusting element aligned with said opening.

4. A dual crystal holder comprising an insulating base, an upstanding metal plate member secured to said base, a pair of vertical insulating bars secured to the side marginal portions of said plate member at one face thereof, said bars being formed with intermediate opposing arms and bottom opposing arms defining an upper rectangular space and a lower rectangular space adjacent said one face of the plate member, said plate member being formed between the intermediate opposing arms with an opening, and an adjustable condenser secured to the opposite face of said plate member and having an adjusting element projecting through said opening,

5. A dual crystal unit comprising a base, an upstanding metal plate member secured to said base, a pair of vertical insulating bars secured to the side marginal portions of said plate member at one face thereof, said bars being formed with intermediate opposing arms and bottom opposing arms defining an upper rectangular space and a lower rectangular space adjacent said one face of the plate member, said plate member being formed between the intermediate opposing arms with an opening, an adjustable condenser secured to the opposite face of said plate member and having an adjusting element aligned with said opening, a crystal plate positioned in each space substantially in contact with said metal plate member. an electrode positioned in each space outwardly adjacent the crystal plate therein, means secured to the outer surfaces of the bars in bridging relation to said spaces, and respective springs positioned between said means and the respective electrodes.

6. A dual crystal holder comprising a base, an upstanding ground plate secured to said base, insulating means secured to one side of said ground plate and formed to define two crystal-receiving cavities with the ground plate as the inner wall of said cavities, said insulating means also dening a space intermediate said cavities, said ground plate being formed with an opening at said intermediate space, and an adjustable condenser secured to the opposite side of said ground plate and having an adjusting element aligned with said opening.

7. A dual crystal holder comprising a base, a ground plate secured to said base, insulating means secured to one side of said ground plate and formed to -dene two crystal-receiving cavities with the ground plate as the inner wall of said cavities, said ground plate being formed with an opening adjacent said cavities, and an adjustable condenser secured to the opposite side of said ground plate and having an adjusting element aligned with said opening.

ROBERT J JAHRLING.

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

UNITED STATES PATENTS Number Name Date 1,688,714 Hund Oct, 23, 1928 2,031,768 Gebhard uu-,- Feb. 25. 1.936

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