Патент USA US2134175код для вставки
Oct. 25, 1938. L. F. CURTIS 2,134,175 WAVE `FILTER Filed June 27, 1956 2 Sheets-Sheet l ll/l INVENTOR. ATTORNEY. oct. 25, 193s. L_ F. CURUS ' 2,134,175 WAVE FILTER Filed June 27, 1956 2 -Sheè’cs-Shee’c 2 25a-'g' ói Z5 \ WQ@ ,4 @MAZ ATTORNEY. Patented Oct. 25, 1938 g A2,134,175 UNITED STATES 2,134,175 ' WAVE FILTER VLeslie Curtis, S‘pring?ìeld„M_ass., assignorrto yUnited American Bosch Corporation, 'Spring field, Mass., a corporation Vof New ,York‘ . Application June 27, 1936, .SerialNo-. _87,711 4 claims. (c1. 17a-'44) This invention relates to radio apparatus and more particularly to a tuned filter circuit for elim inating an undesired frequency from a band of transmitted frequencies. In the past, filters of various kinds have been employed in the antenna circuit- of radio receiv-. ers to minimize the effect of interfering stations and were commonly known as “wave traps”. `In the smaller types of superheterodyne receivers static 'shield'l may be used if necessaryto elimi nate undesired electrostatic' coupling betweenthe inductance 2 or condenser :Sand the outputster-` minals of> the device.~ The inductances. 2 and ,4 _ are magnetically .coupledland'on'e ofthe induct- _ Ol ances is movablysupportedto provide a variable. coupling between.the»-inductances; aslwill ,later `be shown and explained in detail. In Fig.2 there is showna top plan view of the>` the antenna isr connected to the first detector stage and no intervening stage of tuned radio frequency is employed. In such receivers an insulating base. ï The .reference numeralsA indi interfering signal at or near the frequency ¿to Fig. 1 Awill be' applied tolike parts in Fig. Zand Whichüthe intermediate frequency amplifier is tuned will be transmitted directly through the first detecto-r to the intermediate frequency am plifier. Since 465 kilocycles has become almost a standard tuning frequency for the intermediate amplifier, the interference is usually code trans 20 mission from stations- handling ship to shore ' trañìc and operating on frequencies near 465 kilocycles. While filters according to the prior art practice reduced the interference from a particular station, the interfering signal was not eliminated and the reproduction of a desired pro gram suffered accordingly. It is therefore one of the objects of this inven tion to provide a ñlter circuit which shall be more effective in blocking a given transmitted frequency. Another object is to provide a filter circuit which may be included in the> receiver construc component filter elements- as, arranged .onfan y cating the diagrammatic showing of. the parts'in>> the followingiigures. Í ’ .« - ~ The assembly'ismounted:upon a base .8 whichv 16' may be a disk of any suitable insulatingmaterial ,_ such as one of the synthetic resins. lAttached` to the base 8 by> means of.` mounting bolts 9 and nuts l 0 is double alignment condenserofithetype commonly used in intermediate frequency.k trans former's. `The double ¿alignment condenserÍcomf ’ prises a vceramic base" I Iv upon V»which is mounted compression-'type variable lcond'ens'ers - 3 `and`l5 which may beadjusted by the compression screws I4 and I5 respectively. The condenserr 5 has terminals I6 and I 'I which project upwardly through slots in the ceramic base II, and the condenser 3 has similarly arranged terminals I8 and I9. A bow. spring 20 kof non-magnetic material is secured to the ceramic base II byv means of the mounting bolts 9 and extends trans versely over the base II asbest seen in Fig. 3. tion ormay bein the form of a separate unit. Still another object is to provide a filter unit A longitudinal slot is provided in the bow spring ' ' »y which is more stable in construction and requires form supporting the inductance 4. Secured by less frequent adjustment. _ A further object is to provide a filter unit which is more compact in structure and economical in assembly. Other objects and advantages will in part be 40 specifically stated and in part be obvious when the following specification is read in connection with the drawings, in which: Fig. 1 is a schematic diagram of the filter; Fig. 2 is a top view'of the íilter assembly; Fig.,3 is a section taken on line 3-3'of Fig` 2; and Fig. 4 is a botom View of the filter assembly. Referring in more detail to Fig. 1, the numeral I indicates any suitable antenna. A series reso 50 nant circuit comprising an inductance 2 and a variable condenser 3 is connected between the antenna and ground. A parallel resonant circuit comprising inductance 4 and variable condenser 5 is connected in series with the antenna I and to 55 the antenna post of a receiver 6. An electro 20 through which projects a tongue 2I on the coil' a mounting bolt 9 and extending angularly from " . the ceramic base II is a coil bracket 22 of sheet - `metal which supports -the coil form 23 and in ductance 2. The inductances 2 and 4 are each universal wound and in two sections as illustrated 40 by the inductance 2 of Fig. 2. ` In Fig. 3 is shown a cross section of the device taken on line 3--3 of Fig. 2. The movable in ductance >4 is adjusted bythe screw r2li which is carried by a threaded opening inA the mounting strip 25. A metal shell 26 having a mounting bracket 2l is spun over and secured to the insu' lating base disk 8. - Fig. 4 is a bottom View of the device showing the condenser adjusting screws I4and I5 acces- Í sible through >an opening in the base disk 8. The mounting strip 25 is secured by the screws 9 and extends transversely across the opening in the disk 8, carrying the centrally located coil adjust ing screw 24. . ‘ ` ' 55 '2,134,175 In the operation of the device, the series cir cuit comprising inductance 2 and capacity 3 and the parallel circuit comprising inductance 4 and capacity 5 are both tuned approximately to the interfering frequency which is to be elim inated.~ Even though the circuits are tuned ex actly to the undesired frequency, there will be a residual voltage at this frequency due tothe radio lfrequency resistance of the inductances 2 and 4. By suitable regulation of the mutual coupling between the inductances, the< residual voltage in of said frequency differing in phase from the residual voltage of said shunt impedance arm, and means for establishing a mutual coupling relation between said impedance arms, whereby said residual voltages may be substantially elimi nated. 2. In a filter circuit for the attenuation of a predetermined frequency, a shunt impedance arm comprising a series resonant circuit tuned to said frequency'and having a residual Voltage of 10 said frequency across the terminals thereof, a the respective circuits may be made to cancel out ’ series impedance arm comprising a parallel reso nantcircuit tuned to said frequency and having and the terminal voltage at the interferingfre quency will be reduced to substantially Zero.l a residual ,voltage of said frequency differing When the circuits are slightly off tune with the ’ in phase from the residual voltage of said shunt 15 ’ interference, the voltage thereof. may still be re duced to zero by the adjustment of coupling. Inductances having a relatively ‘poor Ypower fac-' tor may be employed in this present device and. 20 so reduce the expense of parts, whereas in the’ prior art devices their eifectiveness depended upon the >reduction of the power factor to the lowest possible values. In tests it has been found that an interfering signal can be reduced on' the order of 30:1 or slightly better by‘ the proper> adjustment of coupling, over Ythe reduc tion possible with the same circuitsv without the . mutual coupling vbetween inductances. It will be obvious that many uses and special 30 applications of the invention exist, other than the particular one illustrated and described. Likewise, many changes and` modifications may be made in the invention by any one skilled in the art without departing from ‘the spirit- and " scope of the invention as set forth in the follow ing claims:y ' V I claim: Y, l. In a filter circuit for the attenuation of a predetermined frequency, a shunt impedance 40 arm tuned to said frequency and having a re sidual voltage; of saidfrequency across the terf minals thereof,> a series impedance arm tuned to said frequency and having a residual voltage impedance arm, and means for establishing a mutual coupling relation between said imped ance arms, whereby said residual voltages may be substantially eliminated. 3. In a ñlter circuit for the attenuation of a predetermined frequency, a shunt impedance arm tuned to said frequency and having a re sidual voltage of said frequency across the ter minals thereof, a series impedance _arm tuned to said frequency and having a residual voltage 25 of said frequency differing in phase from the re sidual Voltage of said shunt impedance arm, and means for combining said residual voltages in one of said impedance arms, whereby they may be substantially eliminated. 30 4. In a filter circuit for the attenuation of a predetermined frequency, a shunt impedance arm tuned to said frequency and havinga re sidual voltage of said frequency across the ter minals thereof, a seriesimpedance arm tuned to 35 said frequency and having a residual voltage of said frequency differing in phase from there sidual Voltage of said shunt impedance arm, and means for impressing upon theshunt impedance arm the residual voltage existing across said 40 series impedance arm, whereby the residual volt age may be substantially eliminated. ‘ _ LESLIE F. CURTIS.