EP0036746A2 - Méthode et appareil pour l'isolation d'une ligne et la protection contre l'interférence pour un système conducteur protégé - Google Patents

Méthode et appareil pour l'isolation d'une ligne et la protection contre l'interférence pour un système conducteur protégé Download PDF

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Publication number
EP0036746A2
EP0036746A2 EP81301118A EP81301118A EP0036746A2 EP 0036746 A2 EP0036746 A2 EP 0036746A2 EP 81301118 A EP81301118 A EP 81301118A EP 81301118 A EP81301118 A EP 81301118A EP 0036746 A2 EP0036746 A2 EP 0036746A2
Authority
EP
European Patent Office
Prior art keywords
interruption
shield
dielectric
isolator
elements
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.)
Withdrawn
Application number
EP81301118A
Other languages
German (de)
English (en)
Other versions
EP0036746A3 (fr
Inventor
Pierre Dobrovolny
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Zenith Electronics LLC
Original Assignee
Zenith Radio Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Zenith Radio Corp filed Critical Zenith Radio Corp
Publication of EP0036746A2 publication Critical patent/EP0036746A2/fr
Publication of EP0036746A3 publication Critical patent/EP0036746A3/fr
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/202—Coaxial filters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B11/00—Communication cables or conductors
    • H01B11/18—Coaxial cables; Analogous cables having more than one inner conductor within a common outer conductor
    • H01B11/1895—Particular features or applications
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/22—Attenuating devices
    • H01P1/225—Coaxial attenuators

Definitions

  • This invention relates generally to the fields of high frequency electromagnetic interference shielding and A.C. power isolation and is more particularly directed to a method and apparatus for the shielding of high frequency shielded conductor systems, such as coaxial cables, from electromagnetic interference and the simultaneous isolation of such conductor systems from sources of A.C. power.
  • the 75 ohm coaxial cable input to a television tuner is a prime example of one type of shielded conductor to which such shielding and isolation is directed.
  • television receivers also include an exposed connection for a 75 ohm coaxial cable input to the receiver's VHF tuner.
  • No U.L. requirement presently exists providing for double isolation of the coaxial input, evidently because the technology has not been available to television manufacturers to enable them to provide such isolation while simultaneously affording acceptable television reception.
  • one prior approach utilizes conventional capacitors coupling the coaxial cable with the tuner input to A.C. isolate the cable from the tuner. While the isolation thus achieved is satisfactory, the field within the cable is inadequately shielded from electromagnetic interference.
  • Another prior approach involves a t.v. antenna isolation assembly designed to effect power line isolation at the antenna input of a television receiver.
  • a number of ferrite beads are loosely fitted around the coaxial cable conductor connected to the 75 ohm input and a number of capacitors are mounted externally of the conductor. While this arrangement provides A.C. line isolation) in fields of strong ambient electromagnetic interference its shielding effect is ineffective.
  • the coaxial cable connected to the 75 ohm input, carries a CATV signal. If the cable includes an A.C. isolator which is an inadequate electromagnetic interference shield, strong co-channel ambient broadcast fields will not be adequately shielded from the field within the coaxial cable and will produce strong co-channel interference.
  • the present invention therefore provides a method and apparatus for accomplishing this aim by providing an interruption in the shield, and situating within the interruption dielectric and magnetically absorptive material selected and disposed to create a capacitive coupling across the interruption to isolate the shield and magnetic absorption within the interruption to absorb energy associated with the ambient electromagnetic interference.
  • a coaxial cable 10 which may be used for carrying a television signal to the tuner of a television receiver.
  • the cable 10 has an inner conductor 12 disposed coaxially within an outer conductor 14.
  • the rightmost end 16 of the cable may be coupled to a signal source and the leftmost end 18 may be coupled to the input of a television tuner.
  • the tuner may be isolated from the A.C. line which powers the receiver.
  • A.C. line which powers the receiver.
  • This prior approach is indicated schematically by capacitors 20 and 22 disposed in the cable's outer conductor.
  • the capacitors 20 and 22 are selected to provide a high impedance at the low frequencies associated with the A.C. line, thereby to further isolate the end 16 of the cable from the line voltage.
  • the inner conductor 12 may also be decoupled from the A.C. line by a capacitor (not shown).
  • the simple capacitive decoupling of the outside conductor can cause an intolerable increase in electromagnetic interference, particularly when a local signal is broadcast on the same frequency as a CATV signal carried by the cable.
  • FIG. 2 shows a preferred embodiment of the invention.
  • a shielded conductor system in the form of a coaxial cable 24 includes an inner conductor 26 and an outer conductor 28.
  • the cable may include a leftmost portion 30 whose outer diameter is greater than the outer diameter of the rightmost portion 32 such that a portion 34 of the larger diameter outer conductor overlaps the smaller diameter outer conductor.
  • the space defined by such overlap constitutes a gap or interruption in which dielectric and magnetically.absorptive material is situated for purposes of shielding and line isolation.
  • the annular, cavity-like interruption thus created holds two discrete elements of dielectric material 36 and 38 separated by an element of magnetically absorptive material 40.
  • Each such element is annular and has a central opening to surround the smaller diameter outer conductor.
  • the elements 36, 38 and 40 may be stacked one against the other and aligned coaxially of the cable as illustrated.
  • the dielectric elements 36 and 38 create a capacitive coupling across the gap between the large and small diameter portions of the outer conductor to isolate the rightmost portion 32 of the outer conductor from the leftmost portion 30. Hence, any A.C. line voltage applied to the leftmost portion 30 is inhibited from reaching the rightmost portion 32.
  • the capacitances formed by the elements 36 and 38 co-operate with the element 40 to shield the field inside the cable 24 from ambient electromagnetic radiation, as described hereinafter.
  • the magnetically absorptive element 40 serves to absorb electromagnetic interference not bypassed by the capacitive effect of elements 36 and 38, without any substantial absorption of the desired field within the cable.
  • Figure 3 shows an equivalent circuit diagram of a two port which may be placed between the cross sections AA (input port) and BB (output port) of Figure 2.
  • the source I represents the current on the outer surface of the outer conductor induced in the vicinity of the cross section AA by the ambient interfering signal.
  • the source E represents the desired signal to be carried by the cable, the resistor Rl represents the nominal output impedance of the source E (75 ohms), and the resistor R2 represents the nominal input impedance (75 ohms) of a television tuner.
  • the resistor R3 represents the equivalent series resistance (100 ohms, for example) of the magnetically absorptive element 40
  • the capacitor Cl represents the capacitance due to the effect of the dielectric element 36
  • the capacitor C2 represents the capacitance due to the effect of the dielectric element 38.
  • Each capacitor Cl and C2 may, by way of example, have a value of about 1000 picofarads.
  • the impedance of the capacitors Cl and C2 is much less than the impedance of any of the resistors in Figure 3.
  • the capacitor Cl shunts the desired signal from source E away from the resistance R3 and toward the input impedance of the tuner. Consequently, the magnetically absorptive material represented by R3 does not substantially absorb any of the desired signal.
  • the capacitor C2 acts to shunt the current I so that the interference current does not develop a substantial corresponding voltage in R2 (the tuner input impedance).
  • capacitor C2 has only a finite capacitance, not all the current I will be shunted. However, capacitors Cl and C2 cause the residual electromagnetic interference to be absorbed by the magnetically absorptive material (R3).
  • any magnetically absorptive material will also produce an equivalent and frequency dependent inductance which is in series with its equivalent resistance. Such inductance may help to suppress interference at lower frequencies, but it is not very desirable at higher frequencies. Hence, the magnetically absorptive material should be selected to maximize interference suppression at the frequencies of interest for a particular application.
  • the dielectric elements 36 and 38 may be of any suitable dielectric material preferably having a high dielectric constant of several thousands to provide a total capacitance of about 2000 picofarads. Barium titante is one example of such dielectric material.
  • the element 40 is made of a magnetically absorp-. tive material whose equivalent series resistance is as high as possible at the frequencies of interest for best absorption of electromagnetic interference.
  • a ferrite material having an equivalent series resistance of about 100 ohms has been found to be acceptable for use at television frequencies.
  • Such a ferrite is available from Fair-Rite Products Corp., Wallkill, New York, referred to as material number 43 or 64.
  • the dielectric elements 36 and 38 may be silver plated inside and outside and soldered to the outer conductor 28 on the inside and to the outer conductor 30 on the outside.
  • the magnetically absorptive element 40 may be in the form of a ferrite bead disposed loosely between the dielectric elements and need not be in physical contact with the cable's outer conductor. It is thought that greater A.C. line isolation may result if no such contact is permitted, particularly in the case where ferrite materials with a high D.C. specific conductance are used.
  • the isolator-cable combination may be used in applications other than with television tuners.
  • the interruption or cavity described above need not be completely disposed in the cable alone.
  • the leftmost portion 30 of the cable (the part of larger diameter) may actually be an input connector to a television tuner.
  • the larger diameter portion of the connector may be extended over the smaller diameter cable so that an area of axial overlap exists as shown, with the dielectric and magnetically absorptive material disposed in the gap defined by the area of axial overlap.
  • an interruption when referred to herein as being in the outer conductor of a cable, it is to be understood that such terminology is meant to also include an interruption between the outer conductor of the cable and a corresponding connection to a tuner input or corresponding structure.
  • the required isolation and shielding may be effected by disposing the interruption at any practical location in a coupling path between the outer conductor of the cable and the input to the tuner or corresponding structure.
  • Such a connector and cable as shown in Figure 2 may be disposed with a television receiver's cabinet.
  • the cable itself need not be flexible as is the case with conventional coaxial cable.
  • the cable may be constructed of conductive pipe having a center conductor.
  • Such a pipe will be understood to be the equivalent of a coaxial cable, wherefore, references herein to a coaxial cable or a shielded conductor are intended to be inclusive of such pipes.
  • the interruption may be implemented without the use of.either a coaxial cable or a conductive pipe. Instead, the interruption may be placed within a connector which is attached directly to a television tuner or corresponding structure. Hence, references herein to a shielded conductor are meant to include such connectors and their equivalents.
  • the isolator of Figure 2 comprising the elements 36, 38 and 40 is illustrated as employing only one ferrite or magnetically absorptive element disposed between a pair of dielectric elements. However, additional dielectric and ferrite elements may be used in an alternating sequence, as shown in phantom at 138 and 140, respectively.
  • the first element on the inside is a dielectric element so that no losses are introduced into the desired signal path.
  • the first element on the outside (element 38 in Figure 2) may be either a dielectric element or a magnetically absorptive element, the former case being more effective.
  • Figure 4 illustrates an isolator in a coaxial cable for radially propagating interference signals and having radially distributed dielectric-ferrite elements.
  • the cable 24a has an inner conductor 26a and an outer conductor 28a.
  • the latter conductor is divided with upturned edges or radial flanges arranged vis-a-vis to form a gap or interruption 42ain which dielectric elements 36a and 38a are separated by a ferrite or other type of magnetically absorptive clement 40a so that the dielectric and magnetically absorptive elements are sandwiched between the flanges and concentrically arranged such that the alternating sequence of elements is in a direction radial to the cable.
  • a greater number of dielectric and magnetically absorptive elements may be employed in alternating sequence in applications where greater performance is desired in spite of the necessarily higher consequent cost.
  • the cable 24b has an inner conductor 26b and an outer conductor 28b, the latter being separated into two ports (left and right, as shown).
  • the ends of the separated parts are interleaved so as to provide a total of at least three spaces between the interleaved parts.
  • a first space contains a dielectric element 36b
  • a second space contains a magnetically absorptive element 40b
  • a third space contains another dielectric element 38b.
  • FIG. 6 Another embodiment is shown in Figure 6 in which the interference signal propagates radially and the isolator elements are distributed axially.
  • an outer conductor 28c of the cable 24c is separated into two parts as shown. The separated parts of the outer conductor are interleaved to provide at least three spaces.
  • a dielectric element 36c is disposed in a first space
  • a magnetically absorptive element 40c is disposed in a second space
  • another dielectric element is disposed in the third space.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
  • Insulated Conductors (AREA)
  • Structure Of Receivers (AREA)
  • Noise Elimination (AREA)
  • Input Circuits Of Receivers And Coupling Of Receivers And Audio Equipment (AREA)
EP81301118A 1980-03-20 1981-03-17 Méthode et appareil pour l'isolation d'une ligne et la protection contre l'interférence pour un système conducteur protégé Withdrawn EP0036746A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US13202080A 1980-03-20 1980-03-20
US132020 1980-03-20

Publications (2)

Publication Number Publication Date
EP0036746A2 true EP0036746A2 (fr) 1981-09-30
EP0036746A3 EP0036746A3 (fr) 1981-12-30

Family

ID=22452075

Family Applications (1)

Application Number Title Priority Date Filing Date
EP81301118A Withdrawn EP0036746A3 (fr) 1980-03-20 1981-03-17 Méthode et appareil pour l'isolation d'une ligne et la protection contre l'interférence pour un système conducteur protégé

Country Status (3)

Country Link
EP (1) EP0036746A3 (fr)
JP (1) JPS56141628A (fr)
CA (1) CA1148626A (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0366965A1 (fr) * 1988-10-31 1990-05-09 The Whitaker Corporation Assemblage de filtre
CN103354450A (zh) * 2012-10-24 2013-10-16 杭州祺来电子有限公司 射频信号地回路隔离器
FR3116646A1 (fr) * 2020-11-26 2022-05-27 Thales Câble de puissance à filtre intégré

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0789623B2 (ja) * 1987-06-06 1995-09-27 日立電線株式会社 密結合信号送受伝送装置

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE902028C (de) * 1943-06-10 1954-01-18 Telefunken Gmbh Breitbandultrahochfrequenzleitung
US2962677A (en) * 1945-10-04 1960-11-29 Bell Telephone Labor Inc Wave guide joint
FR2254864A1 (fr) * 1973-12-18 1975-07-11 Cables De Lyon Geoffroy Delore
FR2275017A1 (fr) * 1974-06-11 1976-01-09 Thomson Csf Dispositif d'attenuation d'ondes parasites tres courtes, utilisable en particulier dans des tubes electroniques, et tubes electroniques comportant de tels dispositifs
US3995193A (en) * 1974-04-20 1976-11-30 Nippon Electric Company, Ltd. Microwave tube having structure for preventing the leakage of microwave radiation

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE902028C (de) * 1943-06-10 1954-01-18 Telefunken Gmbh Breitbandultrahochfrequenzleitung
US2962677A (en) * 1945-10-04 1960-11-29 Bell Telephone Labor Inc Wave guide joint
FR2254864A1 (fr) * 1973-12-18 1975-07-11 Cables De Lyon Geoffroy Delore
US3995193A (en) * 1974-04-20 1976-11-30 Nippon Electric Company, Ltd. Microwave tube having structure for preventing the leakage of microwave radiation
FR2275017A1 (fr) * 1974-06-11 1976-01-09 Thomson Csf Dispositif d'attenuation d'ondes parasites tres courtes, utilisable en particulier dans des tubes electroniques, et tubes electroniques comportant de tels dispositifs

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0366965A1 (fr) * 1988-10-31 1990-05-09 The Whitaker Corporation Assemblage de filtre
US4952896A (en) * 1988-10-31 1990-08-28 Amp Incorporated Filter assembly insertable into a substrate
CN103354450A (zh) * 2012-10-24 2013-10-16 杭州祺来电子有限公司 射频信号地回路隔离器
FR3116646A1 (fr) * 2020-11-26 2022-05-27 Thales Câble de puissance à filtre intégré
EP4006924A1 (fr) * 2020-11-26 2022-06-01 Thales Cable de puissance a filtre integre
US11854722B2 (en) 2020-11-26 2023-12-26 Thales Power cable with integrated filter

Also Published As

Publication number Publication date
JPS56141628A (en) 1981-11-05
CA1148626A (fr) 1983-06-21
EP0036746A3 (fr) 1981-12-30

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Inventor name: DOBROVOLNY, PIERRE