JPS62257287A - Multiplex transmission method for voice and video signals - Google Patents

Abstract

PURPOSE:To easily obtain a reproduced picture excellent in quality by applying a video signal with a low carrier wave frequency moudlation to convert it to an FM signal in 1MHz 10 MHz band, multiplexing it with a voice signal transmitted in baseband<=10kHz, and transmitting it. CONSTITUTION:In a doorbell-camera multiplex transmission system for instance, a slave unit 10 includes a handset 11, a CCD camera 12, an FM moudlator 13, and a multiplexing part 14, while a master unit 20 comprises a branching part 21, a handset 22, a limiter 23, an FM modulator 24, and a monitor television 25. For a cable 30 to connect the slave unit 10 and the master unit 20, for instance, a pair-parallel PVC interior wire is used. A video signal in the baseband of 2-3MHz is frequency-modulated by the FM modulator 13, and its frequency spectrum is expanded to 1.5-6.5MHz, however, the cable 30 can transmit the FM video signal without any attenuation. A band lower than 10kHz is made a voice channel, and a crosstalk between voice and video is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for multiplexing and transmitting audio/video signals, and in particular, technology for transmitting multiplexed signals of audio and video signals via telephone communication lines. Regarding.

(Prior Art) Conventionally, means for baseband transmission of video signals using telephone communication lines has been known. Here, the telephone communication line is not limited to 1. Indoor communication VA (for example, 1) a communication line consisting of two VC-coated 0.65φ single wires arranged in parallel or twisted), but also as an intercom cable. AC wiring river vinyl line used (2010
, 18 strands or 3010. A pair of Tamri wires)
It also includes cables, hereinafter simply referred to as cables. However, such cables are susceptible to the influence of external radio waves, especially
There is a problem in that Jl (590kllz-1350kllz) is guided into the cable and causes beat disturbance in the reproduced image on the receiving end side. In other words, in TV images, even if an interference wave of -30 to -50 dll is superimposed on the amplitude width of the video signal, beats or warp stripes will occur and the image quality will deteriorate. Although it is possible to adopt a differential manual power system, it is difficult to prevent the ingress of medium waves, which have a particularly strong electric field strength.Also, cables may be fixed at regular intervals using steel temples, or iron pipes may be used for cable wiring. Changes in cable environmental conditions are unavoidable as the cable is passed through the cable, and multiple reflections may occur in the cable transmission signal.Especially in signal transmission between 100m and 200m, the frequency transmission characteristics exhibit a uniform drop in the high frequency range. Not only the
Hz) may have dip characteristics of 10 dB or more.

Therefore, in order to obtain a good reproduced image, it may be possible to transmit the video signal using a coaxial cable, but for example,
When installing a camera to take images of visitors in an existing intercom facility, it is inconvenient to lay a coaxial cable separately from the existing cable because it requires a lot of construction work.

(Object of the Invention) The present invention has been made in view of the above circumstances, and it is an object of the present invention to transmit multiple video signals and audio signals via a cable.
The purpose of the present invention is to provide a method for transmitting audio and video signals in multiple formats that can easily reproduce high-quality reproduced images when transmitting C format signals.

(Structure of the Invention) In order to achieve the above object, the present invention has the following structure.

That is, the present invention is a voice/video signal multiplexing transmission method in which a video signal transmitted in one direction or two directions is multiplexed and transmitted on an audio signal transmitted in two directions. IM1 by modulating the video signal with a low carrier frequency
A frequency modulated signal in the 12 to lOMHz band and the frequency modulated video signal as IQ k It z
The multiplexed signal is multiplexed into a baseband transmitted audio signal in the following bands, and the multiplexed signal is transmitted to the receiving side via one or more pairs of telephone communication lines, and the receiving side receives the multiplexed signal. The present invention is characterized in that the resulting signal is demultiplexed into an audio signal and a video signal, and the frequency demodulation is performed after removing an amplitude modulation component from the demultiplexed video signal.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 is a block diagram schematically showing a configuration according to an embodiment of the present invention. The figure shows an intercom camera multiplex transmission system consisting of a slave unit 10 and a base unit 20. The handset 10 includes a handset 11, a CCD camera 12 that images the visitor, an FM modulator 13 that frequency modulates the video signal from the CCD camera 12, and an audio signal and a video signal modulated by 14 wave numbers. and a multiplexing unit 14 that performs multiplexing.

The 11 device 20 includes a demultiplexer 21 that separates the multiplexed signal transmitted from the child ALO into an audio signal and a video signal, a handset 22, and an amplitude modulated video signal separated by the demultiplexer 21. a limiter z3 that removes modulation components;
It includes an FM demodulator 24 that demodulates the frequency table 11F4 video signal from which the amplitude modulation component has been removed, and a television monitor 25 that is provided with the demodulated video signal. The slave unit IO and 11JIi20 are connected by a cable 30.

For this cable 30, for example, a pair of parallel PVC indoor wires (core wire diameter 0.65 mm) is used.

Next, the operation of the embodiment having the above-described configuration will be explained.

First, an example in which the characteristics of the cable 30 (50 m length) used in this example were measured with a characteristic impedance of 140Ω is shown in 2I21, where 650kLl z and 3
Dip at MHz is caused by external radio wave induction, especially the placement position of metal fittings for fixing the cable, and
Characteristic fluctuations greater than lOMIrz are caused by a curve 1 at the transmitting and receiving ends. This means that if you change the cable,
This is inferred from the change in dip frequency. As can be seen from FIG. 2, the cable used in the example has a transmission characteristic of -4 dB up to 10 MHz.

Therefore, by frequency modulating the video signal in the Haasband band 2 to 3 M tl z output from the CCD camera 12 of the child 810 in the FM modulator 13 with a frequency distribution as shown in FIG. extends to the 1.5-6.5 MHz band, and the cable 30 can transmit the frequency-modulated video signal without attenuation.

On the other hand, the audio signal output from the handset 11 is multiplexed with the frequency-modulated video signal in the multiplexer 14. At this time, by setting 10 kHz or less as the audio channel, crosstalk between audio and video can be cut off. Note that by transmitting the audio signal multiplexed with the video signal using the Haze band used in ordinary intercoms, bidirectional transmission can be achieved like a conventional intercom line.

The signals multiplexed in this way are transmitted from the slave unit 10 to the base unit 20 via the cable 30.

By the way, the cable 30 used in this embodiment does not have an electromagnetic shielding effect like a coaxial cable, and has a relatively long transmission span, so electric field leakage to the outside becomes a problem. This matter will be discussed below.

The leakage electric field when transmitting an IVPP frequency liquid 51st video signal using a 0.65 mm diameter parallel 7JJ cable (characteristic impedance 140Ω) is estimated. As shown in Figure 4, if the maximum electric field strength at a point P that is distance/iId away from the cable C is E, then the line current l flows through the minute loop antenna 8 (the hypotenuse in the figure: area ΔS). The electric field strength ΔE induced by ΔE is expressed by the following equation.

λ2r ΔS = w - Δx, = 2π/λ, "=FTr Go] Here, λ is the wavelength corresponding to the line current frequency, " is the distance between point P and minute loop antenna A, and W is the cable 2-core It shows the average interval between.

Now, in calculating the induced electric field strength EP due to the cable current in the section -x, ≦XSX, within the section, 6
− j m r # l.

As a practical example, f-3MHz, λ=t00msd=3
m, w=Q, 0015m, I=0. 003A
(8,4mApr), the leakage electric field strength to a point 3m away from the midpoint is calculated by the cable current per 20m length, (Er) saw #0. Only 3uV/m,
This not only fully satisfies the regulation stipulated in Article 6, Item 1 of the Radio Law Enforcement Regulations (weak radio waves < 3 mH electric field strength 500μV/m), but also Article 26 of the Cable Television Broadcasting Law Enforcement Regulations. Tolerable value of leakage electric field strength specified in (
50μV/m at 3m point) is also a sufficiently satisfactory value. .

The multiplexed signal transmitted via cable 30 is! 1l
The frequency modulated video signal inputted to the demultiplexer 21 of a20 and demultiplexed into an audio signal and a video signal is given to a limiter 23. By setting the limiter 23 to perform a sufficient limiting action, the cable 30 can be
It is possible to sufficiently suppress amplitude modulation components caused by external radio waves mixed in during transmission. Also, due to changes in the environmental conditions surrounding the cable installation, such as fixing the cable with Stella pulls at certain intervals or passing it through a steel pipe, cable transmission is prone to reflections, but the video FM signal Even if it receives amplitude modulation due to multiple reflections, the influence of multiple reflections can be eliminated by the limiter action.

The frequency modulated video signal whose amplitude modulation component has been suppressed in the limiter 23 is demodulated into a video signal in the FM demodulator 1A2S 24 and provided to the television monitor 25.

As mentioned above, since the video signal and the audio signal are band-divided, there is no crosstalk, and the limiter 23 sufficiently suppresses amplitude modulation components caused by external radio waves, etc., so that the signal is not displayed on the television monitor 25. The images produced are of very good quality. Furthermore, even when installing a doorbell camera (for example, the CCD camera 12 in the embodiment) in an existing ink-pong facility, there is no need to install a coaxial cable for transmitting video signals, and the existing telephone line cable can be used. can be used, so 1r Jij of labor 11 costs can be reduced.

In the above embodiment, a pair of parallel PVC indoor wires are connected to cable 3.
0, it is also possible to realize a local videophone system that transmits video signals in both directions as shown in No. 5M.

That is, in the fifth cabinet, the terminal 40 includes a handset 711, a CCD camera 42 that images the speaker, and an FM modulator 43 that frequency modulates the video signal from the CCD camera 42.
The audio signal and the frequency-modulated video signal are split into the multiplexer 1, and the multiplexer 44 splits the transmitted multiplexed signal into an audio signal and a video signal. a limiter 45 that removes the amplitude modulation component from the frequency-modulated video signal; and an FM demodulator 4 that decodes and performs 1AII on the frequency-modulated signal from which the amplitude modulation 213+ component has been removed.
6, and a television monitor 47 on which demodulated video signals can be viewed.

The terminal 50 also has the same configuration as the +'+i terminal 40.

The ◇::;song 40 and the terminal 50 are connected by one rope 60. It is assumed that the transmission characteristics of this cable 60 are similar to those of the cable 30 shown in FIG.

Then, as shown in FIG. 6, the frequency distribution of the frequency modulated video signals transmitted from the terminal 40 and the terminal 50 is within the band of 1=13 MIlz, and each distribution spectrum is ! If I is set so that it does not occur, the above-mentioned pull 60 can transmit this I; Can be corrected,
Images can be reproduced without any reduction in signal-to-noise ratio.

In addition, when transmitting a color signal, the color signal is multiplexed with the luminance signal using NTS C (National Television
isionSystem Co+nm1Ltee) signal or P A L (NaL to Phase 8 ILe)
ion Line) signal, and by frequency modulating the signal, it can be transmitted over the cable. FIG. 6 shows the frequency distribution of a frequency modulation signal in a low band color mode employed in a four-head video tape recorder for broadcasting, as an example of transmitting a color signal by frequency modulating the NTSC signal. As can be seen by comparing the transmission characteristics of the cables shown in the same figure and Fig. 2, the frequency modulated signal shown in Fig. 7 is within the band of approximately 1 to 10 MHz, so this frequency modulated signal is Although the high-frequency components are slightly reduced, this is something that can be easily compensated for. Such a low band color mode is
This was used in early color video tape recorders, but the modulation index was small and it was disadvantageous against tape noise, so soon a bi-band color mode was adopted as tape and head performance improved. The force is 1, and the force is 1.
The main sources of noise in the cable are signal attenuation in the cable and overlap of external radio waves, so the length of the cable is several hundred meters long.
If it is less than m, a sufficient CN ratio (ratio between the R transmission level and the effective value of the random miscellaneous M) can be obtained in most cases, and the system is sufficiently suitable for practical use.

Furthermore, as a means for transmitting a color signal, a luminance signal 1
It is also possible to use a so-called i' CI signal transmission method in which the color difference (number A) is compressed and superimposed during the horizontal blanking period of ) and transmitted in line alternation.

(Effects of the Invention) As is clear from the above explanation, the audio/video signal multiplex transmission method according to the present invention modulates the video signal at a low carrier frequency on the transmitting side and performs frequency modulation in the °ζIMHz-10M It z band. As well as signal, 111 frequency change 1
1g video signal is multiplexed into an audio signal transmitted in baseband in a band of 10 kHz or less, and this multiplexed signal is sent to the receiving side via one or more pairs of telephone communication epsilon wires. It is transmitting. Therefore, according to the present invention, even if an audio signal and a video signal are multiplexed and transmitted using a simple cable 111, the audio signal and the video signal described in iii. are not attenuated during transmission, and Since both of the signals are divided by the bandwidth S, good image transmission can be performed without crosstalk.

Furthermore, even if an amplitude modulation component is mixed into the multiplexed signal due to the influence of foreign radio waves mixed in through the cable or the metal fittings that fix the cable, the present invention can perform amplitude modulation of the frequency-modulated video signal on the receiving side. W2N after removing components
Therefore, the image is not degraded by the amplitude modulation component.

Therefore, according to the present invention, good image transmission can be performed without special installation of a coaxial cable for video signal transmission. Moreover, according to the present invention, for example,
The video signal can be transmitted using the existing intercom cable, and there is no problem even if there is multiple reflection or overlapping of medium waves, so cable wiring work can be done without worrying about overlapping of medium waves or multiple reflections. Therefore, it is possible to easily and inexpensively transmit a multiplexed signal of audio/video signals.

Furthermore, in cases where a door camera is installed on an intercom that transmits audio signals in baseband, the present invention can be implemented by simply adding a video transmission/reception section to the existing intercom facility. The invention is also very practical.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing the configuration of a doorbell camera multiplex transmission method using the audio/video signal multiplex transmission method according to the first embodiment of the present invention, and the second igJ is a single wire with a diameter of 0.65 mm. :, 16 rows 2 core cable (50m length)
3 is a spectral distribution diagram of the frequency modulated video signal in the embodiment, FIG. 4 is an explanatory diagram for estimating the leakage electric field strength from the cable, and FIG. A block diagram showing an outline of the configuration of a local videophone system according to the second embodiment, FIG. 6 is a spectral distribution diagram of a bidirectional frequency modulation video signal in the embodiment shown in FIG. 5, and FIG. 7 is a diagram showing another embodiment. FIG. 3 is an explanatory diagram of an example, and is a spectral distribution diagram of a frequency modulated N T SC signal to be transmitted. 10... Handset, 11... Handset, 12... CC
D camera, 13... FM modulator, 14... Multiplexing section, 20... Base unit, 21... Demultiplexing section, 22... Handset, 23... Limiter, 24...・FM demodulator, 2
5...TV monitor. ni' (henizen WR

Claims (1)

[Scope of Claims] A multiplex transmission method for audio/video signals, in which a video signal transmitted in one direction or two directions is multiplexed with an audio signal transmitted in two directions, and the video signal is transmitted on the transmitting side. 1MHz with low carrier frequency modulation
A frequency modulated signal in a band of ~10 MHz is multiplexed, and the frequency modulated video signal is multiplexed into an audio signal transmitted in baseband in a band of 10 kHz or less, and the multiplexed signal is one of one pair or one pair of multiple pairs. The multiplexed signal is transmitted to the receiving side via the telephone communication line, and the receiving side demultiplexes the multiplexed signal into an audio signal and a video signal, and removes the amplitude modulation component from the demultiplexed video signal. Audio that is characterized by subsequent frequency demodulation
A multiplex transmission method for video signals.