JP2905891B2 - Adapter for TV intercom system and TV intercom system using this adapter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adapter for a television intercom terminal used by being attached to an intercom system using multiplex transmission, and a television intercom system configured using the adapter.

[Related Art] Recently, an intercom system using multiplex transmission has been considered. In such a system, an intercom master unit and an intercom slave unit are connected by a dedicated signal line,
Through the signal lines, the voice signal and the calling signal are modulated and transmitted at different frequencies between both the master unit and the slave unit, and power is supplied to the slave unit from the master unit side. I have.

FIG. 10 is a block diagram showing the configuration of such an intercom system.

In this system, the intercom master unit 100 installed indoors includes a slave unit power supply circuit 101 for supplying power to the slave unit 200 installed at the entrance or the like, and an audio signal (a microphone signal) input from a microphone. The modulation section 105 modulates the high-frequency signal used as the first carrier in FIG. 3), the demodulation section 104 demodulates the modulation signal transmitted from the handset 200 side and extracts the calling signal and the voice signal, and is output from the modulation section 105. In addition to mixing and inputting the modulated signal, the demultiplexing circuit 103 that separates and outputs the modulated signal sent from the slave unit 200 via the signal line 1 to the demodulation unit 104, the modulated signal output from the demultiplexed mixing circuit 103 A power supply superposition circuit 102 including a coil L and a capacitor C is provided for superimposing the power supply current of the power supply circuit 101 for the child device and sending it out from the signal line 1 to the child device 200 side.

In such an intercom master device 100, the modulation section 105 inputs the microphone signal amplified to a certain level by the microphone signal amplification circuit 105b to the modulation circuit 105a, and modulates the high-frequency signal serving as the first carrier with this signal. One demodulation section 104 demodulates the modulated output transmitted from the intercom slave 200 side and output through the demultiplexing / mixing circuit 103, and extracts a voice signal and a call signal. For this reason, the demodulation unit 104 has a configuration including a demodulation circuit 104a, a tone signal detection circuit 104c for extracting a calling signal and a voice signal of the slave 200 from the demodulated signal, and a voice signal amplification circuit 104b. I have.

Further, the other intercom slave 200 includes a modulator 204 and a demodulator 205 corresponding to the intercom master 100 described above. In the modulator 204, the master 100 side generated by the tone signal generation circuit 204c is provided. A second carrier (having a frequency sufficiently different from that of the first carrier in order to prevent interference with the first carrier) in a tone signal or a voice signal amplified by the microphone amplifying circuit 204c as a calling signal to the first carrier. Modulating a high frequency signal. Also, one demodulation section 205 is provided with a demodulation section 205 for demodulating a modulation signal transmitted from the master unit 100 and extracting an audio signal, and a demultiplexing circuit 203 converts a modulation signal output from the demodulation section 204 The signal is sent to the signal line 1, and the modulated signal sent from the master unit 100 via the signal line 1 is sent to the demodulation unit 205.

Further, the slave unit 200 is provided with a power supply separation circuit 201 configured by combining a coil L ′ and a capacitor C ′, and separates the power supply current of the slave unit power supply circuit 101 sent from the parent 100 side. The internal power of the slave unit is taken out.

The connection terminals T1 and TG provided on the master device side and the connection terminals T2 and TG provided on the slave device side are connected to the master device 100 and the slave device 200 by a signal line 1, for example, a coaxial cable. Voice and other control signals required for information communication are multiplex-transmitted between the two via the signal line 1.

The operation of such a system will be described. When a call button (not shown) of the cordless handset 200 is operated, a call signal is generated, a tone signal is output from the tone signal generation circuit 204c of the modulation unit 204, and the modulation circuit 204a The second carrier is FM-modulated with this tone signal. The modulated second carrier is sent to the parent device 100 through the demultiplexing circuit 203 and the power supply separation circuit 201 and further via the coaxial cable 1, and this FM modulated signal is supplied to the power supply superposition circuit 102 and The signal is applied to the demodulation unit 104 via the demultiplexing circuit 103, where the signal is demodulated and the tone signal is detected by the tone signal detection circuit 104c, and the speaker (not shown) of the base unit 100 sounds as a calling signal.

In this way, in the called base unit 100, when a microphone (not shown) responds by sounding a speaker (not shown), the audio signal is amplified by the microphone signal amplifier circuit 105b and sent to the modulation circuit 105a. FM modulation is performed on the first carrier. The FM-modulated first carrier is transmitted to the slave 200 via the coaxial cable 1 through the demultiplexing circuit 103 and the power supply superimposing circuit 102.

Then, in the slave 200 that receives this signal, the FM modulation signal is demodulated by the demodulator 20
The demodulated audio signal is extracted in step 5 and the extracted audio signal is
The signal is amplified at 05b and output from a speaker (not shown) of the child device 200.

Then, a necessary call is made.
The audio signal input from the microphone on the 100 side is FM
After being modulated, the signal is input to the power supply superimposition circuit 102 from the demultiplexing / mixing circuit 103, and further input to the demultiplexing / mixing circuit 203 of the slave 200 via the transmission line 1, where the signal is demultiplexed and then demodulated. The audio signal entered from 205 is output from the speaker as an audio signal.On the other hand, the audio signal input from the microphone of the slave 200 is FM-modulated by the modulation unit, and then input from the demultiplexing circuit 203 to the power supply superimposing circuit 201. The signal is input to the demultiplexing / mixing circuit 103 on the master device 100 side via the transmission line 1, is demultiplexed here, enters the demodulation unit 105, and is output from the speaker as an audio signal.

FIG. 11 is a diagram showing the relationship between these frequencies, in which the DC power supply voltage DC, the base unit modulated wave by the first carrier f1 'and the slave unit modulated wave by the second carrier f2' are mutually different. Frequency multiplex modulation is performed with different frequencies set.

FIG. 12 is a diagram showing a frequency relationship of signals before the modulation of the base unit modulated wave and the slave unit modulated wave. That is, the audio signal has a frequency band of approximately 10 KHz, and the tone signal transmitted at the same time is set to 20 KHz outside the audio signal band to prevent interference.

By the way, when using the above-mentioned intercom system and wanting to further add a monitor TV function to the system, the camera unit and the monitor TV unit are connected by a coaxial cable, and the intercom system is further connected. The TV-camera system must be connected by a control line, which requires time and labor for the laying work, and causes problems such as an increase in the number of signal lines reduced in wiring.

[Problems to be Solved by the Invention] The present invention is proposed in order to solve the above-mentioned problems, and a television that can easily construct a television intercom system simply by adding a connection to an existing multiplex transmission type intercom system. It is an object of the present invention to provide an intercom system adapter and a television intercom system configured using the adapter.

[Means for Solving the Problems] The interphone adapters of the present invention proposed to achieve the above object have the following features.

That is, the first intercom master unit adapter is
Two transmission connection terminals connected to the transmission line, a slave unit power supply circuit for outputting slave unit power to be supplied to the intercom slave unit, and a high-pass filter and a low-pass filter are combined. A wave mixing circuit, a video signal output terminal connected to the input terminal of the monitor television unit via a high-frequency demodulator for video at one end of the branch mixing circuit, A main unit connection terminal connected to an input / output terminal of the intercom master unit provided at one end on the band-pass filter side, and at least an audio signal output from the intercom master unit via the splitter / mixing circuit; A power supply superimposing circuit for superimposing the power supply for the slave unit on the modulation signal including the power supply; There is a example was constructed.

The second intercom master adapter is configured such that a coaxial cable is connected as a transmission line and an unbalanced / balanced conversion circuit is removed.

On the other hand, the first intercom adapter for the intercom has two transmission connection terminals connected to the transmission line, a demultiplexing / mixing circuit configured by combining a high-pass filter and a low-pass filter, and a demultiplexing / mixing circuit. A video signal input terminal for connecting one end of the high-pass filter side of the digital camera to the output terminal of the television camera unit via a video signal modulator, and one end of the low-pass filter side of the branching and mixing circuit is connected to an input of the intercom slave unit. A connection terminal for a slave unit connected to an output terminal and a power supply separation circuit for extracting power for the slave unit from a superimposed output transmitted from the intercom master unit via the transmission line. Unbalanced between terminals /
The balun includes a balance conversion circuit and a matching circuit.

Further, the second adapter for the intercom slave unit has a configuration in which a coaxial cable is connected as a transmission line and a balanced / unbalanced conversion circuit is removed.

Further, the third intercom slave unit has a configuration in which a depolarizing circuit is interposed between the matching circuit and the transmission line connection terminal.

Further, in the first television intercom system, the transmission line is a pair of signal lines, and the multiplex transmission type intercom master unit and the first intercom master unit connected to the monitor television unit are connected via this signal line. An adapter, a multiplex transmission type intercom slave unit, and a first intercom slave unit adapter connected to the TV camera unit are connected to each other, and the second television intercom system is connected to the second intercom master unit. The adapter and the second intercom slave adapter are connected via a coaxial cable.

[Operation] The operation of each invention is as follows.

The first and second intercom master adapters have their transmission line connection terminals connected to a pair of transmission lines and a coaxial cable, the video signal terminal connected to a video signal input terminal of a monitor television, and By simply connecting the unit connection terminal to the input / output terminal of the multiplex transmission type intercom master unit, it can be used as an intercom master unit with a monitor television using the multiplex transmission system.

The first and second intercom slave adapters have their transmission line connection terminals connected to a pair of transmission lines and a coaxial cable, the video signal terminal connected to a video signal output terminal of a television camera, and a child device. By simply connecting the connection terminal to the intercom slave unit, it can be used as a television camera interphone slave unit using a multiplex transmission system.

In the third intercom adapter, the connection polarity of the transmission line is non-polar.

The first and second television intercom systems have a configuration in which signal wiring using a pair of signal lines and a coaxial cable is omitted.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration of a first television intercom system of the present invention constituted by combining a first intercom master adapter and a first intercom slave adapter.

The first adapter 1 for the intercom master unit has a transmission line 3
Connection terminals T1 and T2 to be connected to the main unit and a main unit connection terminal T to be connected to the corresponding input / output terminal of the intercom main unit 5.
3, T4 and a video signal output terminal T5, T6 to be connected to the monitor television unit 4, and a power supply circuit for a slave unit having a power supply superposition circuit 10 therein and a power supply to be supplied to an intercom slave unit described later. 11, a demultiplexing / mixing circuit 12 including a high-pass filter 12a and a low-pass filter 12b, and a transmission line 3
/ Balanced circuit for removing extraneous noise added to the circuit
A balun 13 configured by combining a matching circuit 13b for impedance matching with 13a, and a video signal demodulator 1
It has four.

The connection state of each internal circuit is as shown in the figure. In the power supply superimposing circuit 10, the modulation including at least the call voice signal transmitted from the intercom master device 5 via the branching / mixing circuit 12. The signal is superimposed on the DC power supply of the power supply circuit 11 for the cordless handset, and the superimposed output is further sent to the interphone cordless handset adapter 2 from the terminals T1 and T2 through the transmission line 3 via the balun 13. On the other hand, the modulation signal sent from the intercom slave adapter 2 via the transmission line 3 is separated by the demultiplexer 12 into a video signal modulation band and an audio signal modulation band.

That is, in the branching / mixing circuit 12, the high-pass filter
The modulated wave band of the video signal is separated by 12a, and the modulated wave band of the speech signal is separated by the low-pass filter 12a. Then, the modulated wave band of the separated video signal enters the video signal demodulator 14 and is extracted as a video signal, and the extracted video signal is output to the monitor television unit 4.
The video signal output terminals T5, T
The modulated wave band of the voice communication signal is transmitted to the monitor TV unit 4 via the base station 6 and is transmitted to the intercom master unit 5 via the master unit connection terminals T3 and T4 for processing.

On the other hand, the intercom slave adapter 2 includes transmission line connection terminals T1 and T2 corresponding to the above-described interphone master adapter 1 and slave connection terminals T7 and T8 connected to the corresponding input / output terminals of the interphone slave 6. And a video signal input terminal T9, T10 connected to the television camera unit 7, and a power supply separation circuit for separating the power supply for the slave unit supplied in the form of frequency multiplex modulation from the intercom master unit 1 side.
21, High-pass filter 22a similar to adapter 1 for parent machine
And a low-pass filter 22b, a demultiplexing / mixing circuit 22, an unbalanced / balanced circuit 23a for removing external noise applied to the transmission line 3, and a matching circuit 23b for impedance matching. Balun 23
And a video signal modulator 24.

The connection state of each internal circuit is as shown in the figure. In the power supply separation circuit 21, the power supply for the slave unit is separated from the superimposed output sent from the adapter 1 for the base unit via the transmission line 3. The internal power supply of the adapter.

The video signal output from the television camera unit 7 through the video signal input terminals T9 and T10 is a video signal modulator.
After being modulated by 24, it enters a demultiplexing circuit 22 via a high-pass filter 22a,
The modulated wave band of the communication voice transmitted from the
22 and passes through the low-pass filter 22b.
After being mixed at the transmission line connection terminals T1 and T via the balun 23,
Adapter 1 for intercom master unit through 3 transmission lines from 2
Has been sent to.

Note that between the intercom master unit 5 and the intercom slave unit 6, the modulated wave band of the speech signal generated by each of the modulation units (see FIGS. 2 and 3) is provided by a demultiplexing / mixing circuit 12 provided for each. , 22 are transmitted and received through the low-pass filters 12b, 22b, respectively, and a call is made.

FIG. 2 is an embodiment diagram showing an internal circuit of the intercom master unit used in the present invention.

The intercom master device 5 is connected to the other intercom slave device 6.
(Refer to FIG. 3) The input / output terminals T3 and T4 connected via the transmission line 3 to the slave unit power supply circuit 50 having a power supply to the intercom slave unit as an internal circuit. A modulating unit 51 for modulating a carrier with an audio signal input from a microphone (not shown), a second unit transmitted from the intercom slave unit side;
The demodulation unit 52 demodulates the modulated signal obtained by modulating the carrier with a voice signal and a call signal, sends out the modulation output of the modulation unit 51, and demodulates the modulation signal sent from the modulation unit on the slave unit side via the transmission line. There is provided a branching / mixing circuit 53 to be sent to 52, and a power supply superimposing circuit 54 for superimposing the modulation output from the modulation section 51 on the power supply of the power supply circuit 50 for slave units.

FIG. 3 is an embodiment diagram showing an internal circuit of the intercom slave unit used in the present invention.

The intercom slave device 6 is the intercom master device 5 described above.
Have input / output terminals T7 and T8 connected to each other via a transmission line 3. If both are connected via the transmission line 3, they can be used as they are as an intercom system. The intercom slave unit 6 includes, as an internal circuit, a power supply separation circuit 64 for separating the power supply for the slave unit sent from the intercom master unit side and extracting it as the internal power source of the slave unit, and a microphone (not shown). Modulation unit 6 that modulates with the input audio signal
1. A demodulation unit 62 for demodulating a modulation signal obtained by modulating a first carrier transmitted from the intercom master unit with an audio signal, a modulation signal of the modulation unit 61 is sent to a transmission line via a power supply separation circuit 64, and And a branching / mixing circuit 63 for sending the modulated signal sent from the modulation unit on the master device side to the demodulation unit via the demodulation unit.

FIG. 4 shows a frequency allocation diagram of the modulated frequencies in the frequency multiplexing modulation system used in the system of the present invention, where f1 is the first carrier modulated by the audio signal of the master unit, and f2 is the slave unit. The second carrier f3 modulated by the voice signal and the call signal indicates a video carrier modulated by the video signal modulator, and the carrier frequency is set to be higher in the order of f1, f2 and f3.

Next, a specific example of the internal circuit of each adapter will be described.

FIG. 5 shows an example of a constant current power supply superimposing circuit 10 provided inside the intercom master adapter 1, which is configured to superimpose a constant current on the output of the demultiplexing / mixing circuit 12. , A transistor Q1, resistors R1 to R2, a Zener diode ZD1, a coil L1, and a capacitor C1 as shown in the figure. The input terminal IN is connected to a constant voltage power supply E, and the output terminal OUT is connected to a demultiplexer 12 and a balun 13 in parallel.

In such a variable constant current circuit 11, assuming that the Zener voltage of the Zener diode ZD1 is VZD1, the current Ia supplied to the slave unit is Ia = VZD1 / R2 = const and is kept constant.

The high-frequency signal coming from the demultiplexing / mixing circuit 12 is blocked by the coil L and bypassed by the capacitor C.

FIG. 6 shows an example of the power supply separation circuit 21 provided inside the intercom slave adapter 2.

This circuit consists of two transistors Q3 and Q4, resistors R3-R6,
Diodes D1 and D2 and capacitors C2 to C4 are connected as shown in the figure, a balun 23 and a demultiplexing / mixing circuit 22 are connected in parallel to the input terminal IN, and the internal load of the intercom slave adapter is connected to the output terminal OUT. Connecting.

In such a circuit, when the load current increases, the potential of the capacitor C4 rises, and the voltage between the base and the emitter of the transistor Q3 decreases.
When the load current decreases, the potential of the capacitor C4 decreases and the voltage between the base and the emitter of the transistor Q3 increases. The current increases to act to increase the load current, and a constant current is supplied to the load.

FIG. 7 shows an adapter 1 for an intercom master unit and a slave unit.
2 shows an example of the demultiplexing / mixing circuits 12 and 22 used in any of the two, and has a configuration having a terminal Tc and Th and T1.

The high-pass filter HPF is configured by connecting a coil L with one end grounded as shown in the figure between capacitors C connected in series, and the low-pass filter LPF is configured by a coil L ′ connected in series. , A capacitor C 'having one end grounded is connected. The HPF passes a high frequency higher than the video signal modulation band, and the LPF
It is configured to pass low frequencies below the voice and control signal modulation bands.

FIG. 8 shows a schematic configuration of a second television intercom system of the present invention configured by combining a second intercom master adapter and a second intercom slave adapter.

A feature of the present invention resides in that an unbalanced transmission signal is transmitted and received by using a coaxial cable for the transmission line 3.
Therefore, the intercom master adapter 1 'and the second intercom slave adapter 2' have a simple configuration with the baluns 13 and 23 removed.

In the system of the present invention, the frequency multiplex modulation signal transmitted from the adapter for the parent device to the adapter for the child device includes:
The transmission line has polarity because a DC component serving as a power supply for a slave unit is superimposed.

Therefore, when a pair of signal lines with no distinction in polarity is used for the transmission line itself, it is necessary to consider this polarity when connecting the adapter for the slave unit to the adapter for the master unit. Make connection work cumbersome.

The depolarizing circuit 8 shown in FIG. 9 solves this problem, and is interposed between the transmission line connection terminals T1 and T2 and the balun 23.

The depolarizing circuit 8 forms a diode bridge by combining four diodes D.
IN1 and IN2 are connected to connection terminals T1 and T2 of the adapter for slave unit 2, and output terminals OUT1 and OUT2 are connected to terminals t1 and t2 of the balun 23 (see FIG. 1).

[Effects of the Invention] The effects of each invention are as follows.

The first and second adapters for the intercom master unit are a TV intercom system in which wiring is reduced only by connecting a transmission line to a transmission line connection terminal and additionally connecting a multiplex transmission type intercom master unit and a monitor television. Can be provided.

The adapters for the first and second intercom slave units are connected to a transmission line connection terminal, and additionally connect a multiplex transmission type interphone slave unit and a television camera. Can be provided.

Also, with the third intercom adapter, the connection polarity of the transmission line is non-polar, and wiring can be performed without considering the connection polarity of the transmission line. Becomes easier.

In the first and second TV intercom systems, a TV interphone system having a simplified configuration in which signal wiring using a pair of signal lines and a coaxial cable is omitted is realized.

[Brief description of the drawings]

FIG. 1 shows a first intercom master unit adapter and a first intercom slave unit adapter configured using a first intercom slave unit adapter.
FIG. 2 is a schematic diagram of a first intercom master adapter, FIG. 3 is a schematic diagram of a first intercom slave adapter, and FIG. 4 is a television of the present invention. FIG. 5 is a circuit diagram of an embodiment of a power supply superposition circuit, FIG. 6 is a circuit diagram of an embodiment of a power supply separation circuit, and FIG. FIG. 8 is a circuit diagram of the embodiment, FIG. 8 shows a second interphone master unit adapter and a second interphone slave unit adapter formed using the second interphone slave unit adapter.
FIG. 9 is a schematic configuration diagram of a television intercom system, FIG. 9 is a circuit diagram of an embodiment of a depolarizing circuit provided on the intercom slave adapter side, and FIG. 10 is a schematic configuration of a multiplex transmission type intercom system to which the present invention is applied. FIG. 11 is a layout diagram of carrier frequencies used in the multiplex transmission intercom system, and FIG. 12 is a frequency layout diagram of audio signals and tone signals used in the multiplex transmission intercom system. [Explanation of Symbols] 1 ... Adapter for main unit of intercom 10 ... Power supply circuit for slave unit 11 ... Power supply superimposing circuit 12a, 22a ... High-pass filter 12b, 22b ... Low-pass filter 12,22 ... minute Wave circuit 13a, 23a Unbalanced / balanced conversion circuit 13b, 23b Matching circuit 14 Video signal demodulator 2 Adapter for intercom slave 21 Power supply separation circuit 3 Transmission line 4 Monitor television Unit 5: Interphone master unit 6: Interphone slave unit 7: TV camera unit 8: Depolarizing circuit T1, T2: Transmission line connection terminal T3, T4: Base unit connection terminal T5, T6 ... Video signal output terminal T7, T8: Connection terminal for slave unit T9, T10: Video signal input terminal

Continuation of the front page (72) Inventor Yoshiaki Ueno 1048 Oaza Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Works, Ltd. (56) References JP-A-63-74327 (JP, A) JP-A-53-108209 (JP, A) JP-A-62-227250 (JP, A) JP-A-62-225060 (JP, A)

Claims (7)

(57) [Claims] 1. An intercom system used for composing a television intercom system by adding a monitor television unit and a television camera unit to an intercom system configured by combining an intercom master unit and an intercom slave unit. A) two transmission line connection terminals connected to the transmission line; b) a power supply circuit for a slave unit for supplying power to the intercom slave unit side; c) a high-pass filter and a low-pass filter. A demultiplexing circuit including a band-pass filter; and d) one end of the demultiplexing circuit on the high-pass filter side is connected to a corresponding input terminal of the monitor television unit via a video signal demodulator. A video signal output terminal; and e) an input / output terminal of an intercom master unit provided at one end of the demultiplexing / mixing circuit on the low-pass filter side. A) a connection terminal for the base unit to be connected; and f) a modulation signal including at least an audio signal output from the intercom base unit via the input / output terminal of the demultiplexing / mixing circuit, from the power supply circuit for the base unit. A power supply superimposing circuit for superimposing a power supply for a slave unit; g) an unbalanced / balanced conversion circuit and a matching circuit, the secondary side of which is connected to the output terminal of the power supply superimposed circuit and the primary side of which is connected to the output side. An intercom master unit adapter having a balun connected to two transmission line connection terminals. 2. An intercom system used for composing a television intercom system by connecting a monitor television unit and a television camera unit to an intercom system constituted by combining an intercom master unit and an intercom slave unit. A dexterous adapter comprising: a) two transmission line connection terminals connected to the transmission line; b) a demultiplexer / mixer circuit comprising a high-pass filter and a low-pass filter; c) the demultiplexer. A video signal input terminal for connecting one end of the mixing circuit on the high pass filter side to a corresponding output terminal of the television camera unit via the video signal modulator; and d) one end of the splitting mixing circuit on the low pass filter side. A connection terminal for a slave unit connected to the input / output terminal of the intercom slave unit; and e) a power supply superimposing circuit on the intercom master unit side. A power supply separating circuit for taking out the power for the slave unit from the superimposed output transmitted through the transmission line; f) a balun comprising an unbalanced / balanced conversion circuit and a matching circuit; An adapter interphone adapter for an intercom slave, which is connected to a transmission line connection terminal, and has a secondary side in which an input terminal of the power supply separation circuit and an input / output terminal of the branching mixing circuit are connected in parallel. 3. The interphone master unit adapter according to claim 1, wherein the transmission line is a pair of signal lines, and the interphone master unit adapter and the interphone child unit are connected to the interphone master unit and the monitor television unit via the signal lines. A television intercom system configured by connecting an intercom and the adapter for an intercom slave unit according to claim 2 connected to a television camera unit. 4. The adapter according to claim 1, wherein said transmission line is a coaxial cable, and said adapter for said interphone base unit has a configuration in which a balun is removed. 5. The adapter for an intercom slave according to claim 2, wherein the transmission line is a coaxial cable, and the adapter for the interphone slave is configured so that a balun is removed. 6. The adapter for an intercom base unit according to claim 4, wherein the transmission line is a coaxial cable, and the adapter is connected to the intercom base unit and a monitor television unit via the coaxial cable. A TV intercom system configured by connecting to the intercom slave adapter according to claim 5 connected to a camera unit. 7. The adapter for an intercom slave unit according to claim 2, wherein a depolarizing circuit is further provided on the input side of said transmission line connection terminal.