US2249440A - Wave filter - Google Patents
Wave filter Download PDFInfo
- Publication number
- US2249440A US2249440A US276981A US27698139A US2249440A US 2249440 A US2249440 A US 2249440A US 276981 A US276981 A US 276981A US 27698139 A US27698139 A US 27698139A US 2249440 A US2249440 A US 2249440A
- Authority
- US
- United States
- Prior art keywords
- balanced
- capacities
- terminals
- condensers
- series
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000004804 winding Methods 0.000 abstract description 57
- 230000008878 coupling Effects 0.000 abstract description 24
- 238000010168 coupling process Methods 0.000 abstract description 24
- 238000005859 coupling reaction Methods 0.000 abstract description 24
- 230000005540 biological transmission Effects 0.000 abstract description 12
- 230000001939 inductive effect Effects 0.000 abstract description 9
- 239000013078 crystal Substances 0.000 abstract description 3
- 238000010276 construction Methods 0.000 abstract description 2
- 239000003990 capacitor Substances 0.000 description 56
- 230000001965 increasing effect Effects 0.000 description 12
- 230000003247 decreasing effect Effects 0.000 description 8
- 239000002131 composite material Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
- H03H9/542—Filters comprising resonators of piezoelectric or electrostrictive material including passive elements
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F19/00—Fixed transformers or mutual inductances of the signal type
- H01F19/02—Audio-frequency transformers or mutual inductances, i.e. not suitable for handling frequencies considerably beyond the audio range
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F19/00—Fixed transformers or mutual inductances of the signal type
- H01F19/04—Transformers or mutual inductances suitable for handling frequencies considerably beyond the audio range
- H01F19/06—Broad-band transformers, e.g. suitable for handling frequencies well down into the audio range
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H1/00—Constructional details of impedance networks whose electrical mode of operation is not specified or applicable to more than one type of network
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/42—Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/42—Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns
- H03H7/425—Balance-balance networks
Definitions
- This invention relates to wave filters and more particularly to composite filters made up of more than one section.
- the object of the invention is to increase the attenuation outside of the transmission band in a composite wave filter.
- the overall attenuation outside of the transmission band may be materially reduced by capacitive unbalance due to uncompensated stray capacitances and by inductive unbaiance due to the inequality of nominally equal inductances.
- the capacitive unbalance is reduced by the addition of a properly chosen capacitor connected between an input terminal and either the corresponding output terminal or the diagonally opposite output terminal of the filter.
- a further improvement in the attenuation characeristic may, in general, be obtained by employing two added capacitors, one connected between an input terminal and the corresponding output terminal, and the other connected either between the remaining input and output terminals or between an input terminal and the diagonally opposite output terminal.
- the capacitors are preferably made adjustable to facilitate selection of the proper values.
- the inductive unbalance is reduced by providing at each end of the filter a balanced three-winding transformer having an adjustment by means of which the coupling between the single winding and one of the two balanced windings may be increased while at the same time the coupling between the single winding and the other balanced winding is decreased.
- the transformer is preferably provided with a further adjustment for varying the coupling between the single winding and the two balanced windings in series so that the transformer may be adjusted to transmit the required band of frequencies.
- a suitable embodiment of the transformer is disclosed in which the two balanced windings are wound upon a hollow cylinder and the single winding is supported within the cylinder. Provision is made for adjusting the position of the inner coil longitudinally with respect to the outer windings and for adjusting the angle between the axes of the inner and the outer coils.
- Fig. 1 is a schematic showing of a two-section wave filter with balancing capacitors in accordance with the invention
- Fig. 2 is an equivalent lattice network representing the stray capacitances effective between the input and output terminals of the filter of Fig. 1;
- Fig. 3 shows the circuit of ⁇ a specific embodiment of the invention including balancing capacitors and end transformers with adjustments for balance;
- Fig. 4 is a cross-section of a suitable three- Winding transformer having special adjustments.
- Fig. 5 is a perspective view of the sliding member and inner coil of the transformer of Fig. 4.
- Fig. 1 shows diagrammatically a composite wave filter comprising a plurality of sections, such as 5 and 6, connected in tandem between a pair of input terminals i 2 and a pair of output terminals 3, 4.
- the individual sections may be of any type but it is assumed that the filter as viewed at either end is a balanced structure.
- the capacitors CA and CB, each connected between an input terminal and an output terminal, are added in accordance with the invention to balance the stray capacitances associated with the component filter elements and thereby increase the attenuation of the filter outside of the transmission band.
- a third capacitor such as Co, is required.
- the capacitors are preferably made adjustable, as indicated by the arrows.
- Fig. 2 shows ⁇ the equivalent lattice network representing the stray capacitances effective between the terminals oi' the filter of Fig. l.
- the capacitances C13 and C24 forming the series branches of the lattice represent, respectively, the stray capacitances effective between each input terminal I, 2 and the corresponding output terminals 3, 4.
- the capacitances C14 and C23 in the diagonal branches represent, respectively, the stray capacitances effective between each input terminal l, 2 and the diagonally opposite output terminals 4, 3.
- all of the four capacitances forming the lattice will have different values and there is thus provided, in effect, a second transmission path in parallel with the normal path through the filter sections.
- Equation 1 The effects of the longitudinal current in the output load may also be eliminated by the addition of only two capacitors so proportioned and so placed that the unbalance voltage to ground at the input end of the lter is made equal in magnitude to, but 180 degrees out of phase with, the unbalance voltage to ground at the output end.
- Equation 1 must be satised and in addition the two series capacitances must be made equal.
- the latter condition in equation form is The choice of the branches to which the capacitors are to be added is based upon the following considerations. Since the two series branches are to be equal it is seen from Equation 1 that each series capacitance must be equal to the geometric mean of the two diagonal capacitances. That is,
- each series capacitance is smaller than the geometric mean of the diagonal capacitances
- a capacitor is added to each series branch and its value is so chosen that the total capacitance of each series branch is equal to this mean.
- the capacitors CA and Cc of Fig. 1 are used.
- the smaller series capacitance is built out to the Value of the larger by the addition of a capacitor and either of the diagonal capacitances is built out by the addition of a second capacitor of such a value that the product of the series branches is equal to the product of the diagonal branches.
- the capacitors CA and CB may, for example, be used.
- Fig. 3 shows an embodiment of the invention in a two-section filter which includes balancing capacitors to reduce the capacitive unbalance and balanced three-winding transformers with special adjustments to reduce the inductive unbalance.
- 'I'he two sections have similar circuit configurations and are designed to pass the same band of frequencies.
- Each section is of the differential transformer type in which 'the transmission through a piezoelectric crystal impedance is balanced against the transmission through an impedance of different character, for example, a capacitor.
- the two impedances are so proportioned that substantially complete balance is obtained at all frequencies except those falling in the transmission band.
- One section of the lter comprises a threewinding transformer T1, a piezoelectric crystal X1 and a balancing capacitor C1, and the other sec-tion includes the corresponding elements T2, X2 and C2.
- the two sections are connected in tandem back-to-back, with the transformers at the outer ends, so that the composite lter is symmetrical and is seen as a balanced structure at the input terminals l, 2 and also at the output terminals 4.
- the capacitors CA and CB are added to reduce the capacitive unbalance caused by the stray capacitances shown in Fig. 2 which are effective between the various lter termonals.
- the capacitance CA is connected between terminals 2 and 4 and is given a value equal to .the difference between C13 and C24.
- the capacitance CB is now added to a diagonal branch, for example, between terminals l and 4, as shown. and given such a value that the product of the series branch capacitances is equal to the product of the diagonal branch capacitances.
- the capacitance Cn may be connected between terminals 2 and 3.
- the capacitance CA may be connected between terminals I and 3, and CB may be connected either between terminals l and 4, as shown, or between terminals 2 and 3.
- the capacitance CA may be connected as shown between terminals 2 and 4 and CB connected between terminals I and 3, and their values so chosen that the total capacitance of each series branch is equal to this mean. Also, as explained above, considerable improvement may be obtained by the use of a single balancing capacitor.
- the two balanced windings W1 and W2 are equal in inductance and are closely coupled.
- the third inductance W3 is inductiveiy coupled to the balanced windings.
- the two variable capacitors C3 and C4 are connected in shunt at the respective ends of the transformer and adjusted to resonate with the associated induetances at the mid-band frequency of the filter in order to decrease the transmission loss introduced by the transformer.
- an adjustment is provided by means of which the coupling between W3 and Wi can be increased or decreased while at the same time the coupling between W3 and W2 is decreased or increased.
- the output transformer T2 is of similar construction and comprises the windings W4, Ws and W and the capacitors C5 and C6.
- the loads may be connected directly to the input terminals I, 2 and the output terminals 3, 4, in which case the windings W3, We and the associated tuning capacitors C3, C5 may be omitted.
- the loads are connected to the input terminals II, I2 and the output terminals.
- I3, I4 and the filter may be used in either balanced or unbalanced circuits.
- a suitable structure for the three-winding transformer T1 is shown in cross-section in Fig. 4.
- the balanced windings W1 and W2 are wound on the tube 20, and the third winding W3 is placed on a smaller tube 2
- the slide 22 has beveled edges 23, 2li, which t into the oppositely disposed longitudinal grooves 25, 26 in the inner surface of the tube 20.
- One end of the slide has a slot 21 leading to a circular hole 28 which has a diameter somewhat larger than the width of the slot.
- Each end of the tube 2I has a pair of notches 30, 3I which permit the tube to be slid through the slot 21 into the hole 28.
- the distance between diagonally opposite notches is equal to the diameter of the hole and therefore the tube is supported at at least three points, such as 33, 34 and 35.
- the angle between the axis of the inner coil W3 and axis of the outer windings W1 and W2 can be adjusted, and therefore the inductive coupling between these coils can be set at the required value.
- the inner coil W3 may be displaced to one side or the other of a central position, and in this way the coupling between the single winding W2 and one of the balanced windings, say W1, may be increased while at the same time the coupling between W3 and the other balanced winding is decreased.
- This latter adjustment does not affect appreciably the coupling between W3 and the two balanced windings in series, as this is dependent primarily upon the angle between the axes of the coils.
- a balanced wave filter comprising a pair of input terminals, a pair of output terminals, a plurality of sections connected in tandem between said pairs of terminals, and means for reducing the capacitive unbalance due to stray capacitance comprising an added capacitor connected between an input terminal and an output terminal whereby the attenuation of the filter outside of the transmission band is increased.
- a wave filter in accordance with claim 1 in which said capacitor is connected between an input terminal and the corresponding output terminal.
- a wave filter in accordance with claim 1 in which said capacitor is connected between an input terminal and a diagonally opposite output terminal.
- a balanced wave filter comprising a pair of input terminals, a pair of output terminals, a plurality of sections connected in tandem between said pairs of terminals, and means for reducing the capacitive unbalance due to stray capacitance comprising a plurality of added capacitors, each of said capacitors being connected between an input terminal rand an output terminal, whereby the attenuation of the filter outside of the transmission band is increased.
- a wave filter in accordance with claim 5 in which two of said capacitors are connected respectively between each of the input terminals and the corresponding output terminal.
- a wave filter in accordance with claim, 5 in which one of said capacitors is connected between an input terminal and the corresponding output terminal and another of said capacitors is connected between an input terminal and the diagonally opposite output terminal.
- a Wave filter in accordance with claim 5 in which two of said capacitors are connected respectively between each of the input terminals and the corresponding output terminal and another of said capacitors is connected between an input terminal and the diagonally opposite output terminal.
- a balanced wave iilter comprising a plurality ⁇ of sections connected in tandem between a pair of input terminals and a pair of output terminals, means for reducing the capacitive unbalance due to unequal stray capacitances effective between said terminals comrprising an added capacitor connected between an input terminal and an output terminal, the capacitance of said capacitor being so proportioned with respect to said stray capacitances that the product of the capacitances effective between each input terminal and the corresponding output terminal isA substantially equal to the product of the capacitances effective between each input terminal and the diagonally opposite output terminal.
- a balanced wave filter comprising a plurality of sections connected in tandem between a pair of input terminals and a pair of output terminals, means for reducing the capacitive unbalance due to unequal stray capacitances effective between said terminals comprising a plurality of added capaci-tors, each of said capacitors being connected between an input terminal and an output terminal, and the capacitances of said capacitors being so proportioned with respect to said stray capacitances 'that the capacitances effective between each input terminal and the corresponding output terminal are substantially equal and their product is substantially equal to the product of the capacitances effective between each input terminal and the diagonally opposite output terminal.
- a balanced wave filter comprising means for reducing inductive unbalance including a three-winding transformer comprising a single winding and two substantially balanced windings, said transformer having an adjustment for increasing the coupling between said single winding and one of said balanced windings while at the same time decreasing the coupling between said single winding and the other of said balanced windings.
- a balanced wave lter comprising a pair of input terminals, a pair of output terminals and a plurality of sections connected in tandem between said pairs of terminals, each end section of said lter including a three-winding transformer for connecting said filter with one of its terminal loads, each of said transformers comprising two substantially equal windings connected in series between one of said pairs of terminals, a third winding, and means for increasing the coupling between said third winding and one of said equal windings while decreasing the coupling between said third winding and the other of said equal windings.
- a wave filter in accordance with claim 14 which includes a capacitor connected between an input terminal and an output terminal to reduce the capacitive unbalance.
- a wave iilter in accordance with claim 14 which includes a plurality of added capacitors for reducing the capacitive unbalance, each of said capacitors being connected between an input terminal and an output terminal.
- each of said transformers includes additional means for adjusting in the same direc- 'tion the coupling between said third winding and both of said equal windings.
- a balanced wave lter comprising a pair of input terminals, a pair of output terminals, a plurality of sections connected in tandem between said terminals, and an added capacitor connected between an input terminal and an output terminal and adjusted to decrease the capacitive unbalance due to stray capacitance, each end section of sail lter including a threewinding transformer for connecting the lter to a terminal load and each of said transformers comprising a single winding and two balanced windings and including means for increasing the coupling between said third winding and one of said balanced windings while decreasing the coupling between said third winding and the other of said balanced windings.
- each of said transformers includes additional means for adjusting in the same direction the coupling between said third winding and both of said balanced windings.
- a wave filter in accordance with claim 18 which includes a second added capacitor connected between an input terminal and an out put terminal and adjusted to further decrease the capacitive unbalance.
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Multimedia (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Coils Or Transformers For Communication (AREA)
- Filters And Equalizers (AREA)
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NL58138D NL58138C ( ) | 1939-06-02 | ||
US276981A US2249440A (en) | 1939-06-02 | 1939-06-02 | Wave filter |
GB5685/40A GB534603A (en) | 1939-06-02 | 1940-03-29 | Wave filters |
CH255231D CH255231A (de) | 1939-06-02 | 1944-11-17 | Wellenfilter. |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US276981A US2249440A (en) | 1939-06-02 | 1939-06-02 | Wave filter |
Publications (1)
Publication Number | Publication Date |
---|---|
US2249440A true US2249440A (en) | 1941-07-15 |
Family
ID=23058943
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US276981A Expired - Lifetime US2249440A (en) | 1939-06-02 | 1939-06-02 | Wave filter |
Country Status (4)
Country | Link |
---|---|
US (1) | US2249440A ( ) |
CH (1) | CH255231A ( ) |
GB (1) | GB534603A ( ) |
NL (1) | NL58138C ( ) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3284728A (en) * | 1961-09-22 | 1966-11-08 | Siemens Ag | Electromechanical filter |
US3287669A (en) * | 1961-09-22 | 1966-11-22 | Siemens Ag | Electromechanical band filter having bridging capacitor for providing attenuation pole |
-
0
- NL NL58138D patent/NL58138C/xx active
-
1939
- 1939-06-02 US US276981A patent/US2249440A/en not_active Expired - Lifetime
-
1940
- 1940-03-29 GB GB5685/40A patent/GB534603A/en not_active Expired
-
1944
- 1944-11-17 CH CH255231D patent/CH255231A/de unknown
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3284728A (en) * | 1961-09-22 | 1966-11-08 | Siemens Ag | Electromechanical filter |
US3287669A (en) * | 1961-09-22 | 1966-11-22 | Siemens Ag | Electromechanical band filter having bridging capacitor for providing attenuation pole |
Also Published As
Publication number | Publication date |
---|---|
CH255231A (de) | 1948-06-15 |
NL58138C ( ) | |
GB534603A (en) | 1941-03-11 |
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