US3919490A - Crosstalk prevention in interphone systems and the like - Google Patents

Crosstalk prevention in interphone systems and the like Download PDF

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Publication number
US3919490A
US3919490A US408589A US40858973A US3919490A US 3919490 A US3919490 A US 3919490A US 408589 A US408589 A US 408589A US 40858973 A US40858973 A US 40858973A US 3919490 A US3919490 A US 3919490A
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United States
Prior art keywords
receiver
crosstalk
switching means
signal
coupled
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Expired - Lifetime
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US408589A
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English (en)
Inventor
Shigemasa Ichikawa
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.)
Aiphone Co Ltd
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Aiphone Co Ltd
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Publication date
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Publication of US3919490A publication Critical patent/US3919490A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M1/00—Substation equipment, e.g. for use by subscribers
    • H04M1/738—Interface circuits for coupling substations to external telephone lines
    • H04M1/74—Interface circuits for coupling substations to external telephone lines with means for reducing interference; with means for reducing effects due to line faults

Definitions

  • ABSTRACT In an interphone unit and the like including a transmitting microphone and a receiver. there are provided means for rectifying one part of the input signal into a dc. signal and switching means connected in series with the receiver, the switching means being operated depending on the magnitude of the output d.c. signal from the rectifying means, whereby weak crosstalk signals are prevented from passing through the receiver and only communication signals are passed therethrough.
  • This invention relates generally to crosstalk preventing techniques and more particularly to a circuit for an interphone unit and the like which is connected with a great number of similar units for communication therebetween.
  • multiconductor cables each including a great number of conductors disposed in parallel (not in the form of twisted pairs) are used for interconnecting these unitsaOf these conductors, only one is used for a common return line of the system, and the rest of the conductors are usedfor individual communication lines.
  • the crosstalk in an interphone system and the like occurs because of the following reasons.
  • Electromagnetic inductions also exist between the conductors, and some part of. the crosstalk is caused through the electromagnetic inductions.
  • the commonly provided return line always .includes some resistance and, hence, causes a voltage drop as a communication current flows through the return line. Such a voltage drop inevitably deleteriously affects the communications through other conductors related to the common return line.
  • a primary object of the present invention is to provide an improved organization of the circuit for an interphone unit and the like, whereby any crosstalk caused therein can be eliminated .effectively without requiring any complicated circuitry.
  • Another object of the invention is to provide an improved circuit for an interphone unit and the like whereby any crosstalk can be prevented from entering into the receiver. regardless of the electric resistance normally existing in the common return line.
  • Still another object of the invention is to provide an improved circuit for eliminating crosstalk in an interphone system and the like, wherein the differencebetween the energy levels of the communication signal 2 and the crosstalk signal is utilized for preventing the crosstalk from entering into the receiver.
  • an improved circuit according to the invention for an interphone unit and the like including a transmitting microphone and a receiver, which circuit comprises means for rectifying one part of the input signal into a dc signal and switching means connected in series with the receiver, the switching means being operated depending on the magnitude of the do. output signal from the rectifying means, whereby weak crosstalk signals are prevented from passing through the receiver, and communication signals of greater magnitudes than the crosstalk signals are thereby allowed to pass through the receiver.
  • FIG. 1 is a schematic circuit diagram showing an interphone system and the like having two communication lines and a return line;
  • FIG. 2 is a graphical representation showing the relation between the crosstalk voltage and the resistance of the common return line.
  • FIG. 3 is a circuit diagram of an interphone unit and the like wherein a crosstalk preventing circuit is provided according to the present invention.
  • the communication current i, with respect to a line transmitting voltage e which is divided into a return line current i, and a crosstalk current i can be expressed as follows.
  • crosstalk voltages e, and 6 appearing across the load impedances Z and Z respectively can be expressed as follows.
  • FIG. 3 indicating a typical example of an interphone unit.
  • a communicating terminal 1 and power source terminals 2 and 3 are provided in the interphone unit, and between the power source terminals 2 and 3, there are connected in series a transmitting microphone T and a biasing resistor R for the microphone T.
  • the output of the microphone T is coupled to the communication terminal 1 through a required number of coupling capacitors such as C, and C
  • the receiver R in this unit is connected through the coupling capacitor C between the communication terminal 1 and one terminal 2 of the power source terminals, which is further connected to a common return line of the interphone system.
  • a crosstalk preventing circuit comprising a switching transistorQ inserted between the coupling capacitor C and the receiver R.
  • the collector of the transistor is further connected to the power source terminal 3 through a collector resistor R,.
  • the base of the transistor 0 is connected through a base resistor R to an amplifier-rectifier combination 4 which is in itself of a well known organization including an amplifying transistor Q and a voltage multiplying rectifier.
  • the collector of the transistor 0 is connected through a resistor R to the power source terminal 3, and the base thereof is connected through a biasing resistor R to the collector.
  • the voltage-multiplying rectifier comprises rectifying diodes D and D and a smoothing capacitor C and the input side thereof is connected to the collector of the amplifying transistor Q through a coupling capacitor C,, while the output side thereof is coupled through the base resistor R to the base of the switching transistor Q
  • the crosstalk preventing circuit operates as follows. When a weak crosstalk signal is applied across the terminals 1 and 2,
  • the signal is passed through the capacitors C, and C to the amplifying transistor Q of the amplifier-rectifier combination 4.
  • the signal is amplified therein and rec tified into a dc. voltage ofa value substantially equal to a multiple ofits initial value.
  • the circuit is so composed that the bias current thus applied to the switching transistor O is not sufficient to bring the switching taansistor Q into the conducting state, the entrance of the crosstalk into the receiver R is completely prevented.
  • crosstalk can be prevented from entering the receiver effectively even in an interphone system wherein the number of required conductors is reduced to substantially one half of the interphone system employing twisted pairs of conductors.
  • circuit according to the invention may also be applied to a similar system such as an interphone system and the like. Furthermore, the circuit may also be combined into the conventional interphone system with a simple modification'thereof.
  • an interphone system including a plurality of units, each unit having a transmitting microphone, a receiver, a common terminal and at least one power source terminal, said transmitting microphone and said receiver both being coupled to said common terminal and to one power source terminal, the improvement which comprises a circuit for preventing crosstalk comprised of a combination amplifier-rectifier means having input and output sides, the input side thereof being coupled to said common terminal, said combination means rectifying one part of an input signal received by said unit at said common terminal into a d.c. signal, and switching means connected in series with said receiver and coupled to the output side of said combination means and controlled thereby, said switching means being normally open, thereby maintaining said receiver in an inoperative state, and being switched to a closed state by a d.c.
  • said predetermined level being set so that only communication signals, rather than crosstalk from other units, switch said switching means to the closed state, said receiver being activated when said switching means is closed, whereby weak crosstalk signals are prevented from passing through the receiver and only communication signals are passed therethrough.
  • switching means is a switching transistor having a base, emitter and collector, said base being coupled to the output side of said combination means.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Interconnected Communication Systems, Intercoms, And Interphones (AREA)
US408589A 1973-03-30 1973-10-23 Crosstalk prevention in interphone systems and the like Expired - Lifetime US3919490A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP48037315A JPS49123706A (cs) 1973-03-30 1973-03-30

Publications (1)

Publication Number Publication Date
US3919490A true US3919490A (en) 1975-11-11

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ID=12494237

Family Applications (1)

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US408589A Expired - Lifetime US3919490A (en) 1973-03-30 1973-10-23 Crosstalk prevention in interphone systems and the like

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US (1) US3919490A (cs)
JP (1) JPS49123706A (cs)
DE (1) DE2361721A1 (cs)
IT (1) IT1003170B (cs)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4256232A (en) * 1978-12-05 1981-03-17 Celanese Corporation Powder composition and method of preparation

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3189691A (en) * 1960-04-27 1965-06-15 Modern Telephones Great Britai Two-way telephone systems with talk-listen switching
US3286031A (en) * 1963-03-04 1966-11-15 Alto Scient Co Inc Voice actuated device
US3567868A (en) * 1968-08-27 1971-03-02 Tokyo Shibaura Electric Co Interphone device having presence indicator means
US3610835A (en) * 1970-03-17 1971-10-05 Bell Telephone Labor Inc Loudspeaking telephone
US3691311A (en) * 1970-12-10 1972-09-12 Pacific Plantronics Inc Telephone user set
US3725585A (en) * 1972-03-21 1973-04-03 Itt Loudspeaking telephone station circuit
US3742153A (en) * 1970-09-03 1973-06-26 Nippon Telegraph & Telephone Telephone circuit for sidetone balance and automatic transmission level adjustment
US3743950A (en) * 1972-03-03 1973-07-03 Itt Threshold detector for a voice frequency receiver

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3189691A (en) * 1960-04-27 1965-06-15 Modern Telephones Great Britai Two-way telephone systems with talk-listen switching
US3286031A (en) * 1963-03-04 1966-11-15 Alto Scient Co Inc Voice actuated device
US3567868A (en) * 1968-08-27 1971-03-02 Tokyo Shibaura Electric Co Interphone device having presence indicator means
US3610835A (en) * 1970-03-17 1971-10-05 Bell Telephone Labor Inc Loudspeaking telephone
US3742153A (en) * 1970-09-03 1973-06-26 Nippon Telegraph & Telephone Telephone circuit for sidetone balance and automatic transmission level adjustment
US3691311A (en) * 1970-12-10 1972-09-12 Pacific Plantronics Inc Telephone user set
US3743950A (en) * 1972-03-03 1973-07-03 Itt Threshold detector for a voice frequency receiver
US3725585A (en) * 1972-03-21 1973-04-03 Itt Loudspeaking telephone station circuit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4256232A (en) * 1978-12-05 1981-03-17 Celanese Corporation Powder composition and method of preparation

Also Published As

Publication number Publication date
DE2361721A1 (de) 1974-10-17
JPS49123706A (cs) 1974-11-27
IT1003170B (it) 1976-06-10

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