Multiplex transmission of audio signal and video signal through inhouse cable

• US 4,955,048 A
• Filed: 03/13/1989
• Issued: 09/04/1990
• Est. Priority Date: 04/30/1986
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Itsumi, Tadashi, Murakami, Satoshi, Iwamura, Soichi
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): Chan, Wing F.
• Application Number:
  US07/323,197
• Time in Patent Office: 540 Days
• Field of Search: 379/53, 379/54, 379/103, 358/12, 358/15, 358/16, 358/85, 358/142, 358/143, 358/19
• US Class Current: 348/14.13
• CPC Class Codes: H04N 7/10 Adaptations for transmission by electrical cable H04N7/12 takes precedence
• CPC Class Codes: H04N 7/148 Interfacing a video terminal to a particular transmission medium, e.g. ISDN
• CPC Class Codes: H04N 7/186 Video door telephones

Abstract

In a method for multiplexing the transmission of audio and video signals, the video signal is separated into a luminance signal and a chrominance signal. The luminance signal is then modulated, and the chrominance signal is balanced-modulated with a low-frequency carrier. The chrominance signal is then converted to a lower frequency. The audio signal, frequency-modulated luminance signal and frequency-converted chrominance signal and frequency-converted chrominance signal are multiplexed by frequency division to be transmitted across telephone cable. Consequently, in comparison with the conventional transmission method which executes direct frequency modulation of the video signal, the band-width of the frequency-modulated luminance signal becomes narrower to eventually facilitate multichannel transmission. The harmful influence from interference from external radio waves or from metallic members used to fix the cable is removed on the receiver side. Accordingly, satisfactory picture transmission can be performed without the necessity of any additional coaxial cable for video signal transmission.

Claims

1. A method for transmitting and receiving multiplexed audio-video signals between two sets of transmitters/receivers, one transmitter/receiver set at each of a first and second station, by a pair of telephone communication cables, by multiplexing baseband audio signals and video signals, the baseband audio signals being bidirectional, comprising the steps of:

(a) frequency modulating the video signals at said first station with a first low frequency carrier;

(b) multiplexing the frequency-modulated video signals of step (a) with the baseband audio signals at said first station;

(c) frequency modulating the video signals of said second station with a second low frequency carrier, different from said first low frequency carrier;

(d) multiplexing the frequency-modulated video signal of step (c) with baseband audio signals at said second station such that said multiplexed signals at each of said first and second stations both operate at different frequencies;

(e) simultaneously transmitting each of the multiplexed signals of steps (b) and (d) through the pair of telephone communication cables in a bidirectional manner;

(f) separating the multiplexed signals of step (d) and (b) into audio signals and frequency-modulated video signals at each of said first and second stations respectively;

(g) removing an amplitude component from each of the separated frequency-modulated video signals of step (f);

(h) frequency demodulating each of the frequency modulated video signals of step (g), thereby allowing bidirectional transmission of the audio and video signals.

2. The method as claimed in claim 1, wherein the low frequency carrier of step (a) is within a frequency range of 1 to 10 MHz, and the baseband audio signal of step (b) is being transmitted in step (c) below 10 KHz.

3. A method for transmitting and receiving multiplexed audio-video signals through a pair of telephone communication conductors by multiplexing a baseband audio signal and a video signal, comprising the steps of:

(a) separating an original video signal into a luminance signal and a chrominance signal;

(b) frequency modulating the separated luminance signal of step (a) with a low-frequency carrier;

(c) converting the separated chrominance signal of step (a) to a frequency lower than an original frequency of the chrominance signal;

(d) multiplexing the baseband audio signal, the frequency-modulated luminated signal of step (b), and the frequency-converted chrominance signal of step (c) by frequency division;

(e) transmitting the multiplexed signal of step (d);

(f) separating the transmittal signal of step (e) into a baseband audio, a frequency modulated luminance signal, and a frequency converted chrominance signal;

(g) frequency demodulating the frequency-modulated luminance signal of step (f);

(h) converting the frequency-converted chrominance signal of step (f) to the original frequency of the chrominance signal; and

(i) combining the signals of steps (g) and (h) to obtain the original video signal of step (a).

4. The method as claimed in claim 3, wherein the method further comprises the steps of:

(j) frequency modulating the chrominance signal of step (a) before accomplishing step (c); and

(k) pre-emphasizing the luminance signal of step (a) before accomplishing step (b), by emphasizing a high-frequency component of the luminance signal.

5. The method as claimed in claim 4, wherein the method further comprises the steps of:

(l) low pass filtering the luminance signal of step (a) before accomplishing step (k);

(m) band pass filtering the chrominance signal of step (a) before accomplishing step (j);

(n) high pass filtering the frequency-modulated luminance signal of step (b) before accomplishing step (d);

(o) band pass filtering the frequency-converted chrominance signal of step (c) before accomplishing step (d); and

(p) low pass filtering of the baseband audio signal before accomplishing step (d).

6. The method as claimed in claim 5 wherein the method further comprises the steps of:

(q) removing an amplitude component of the frequency-modulated luminance signal of step (f) before accomplishing step (g).

7. The method as claimed in claim 6, wherein the method further comprises the steps of:

(r) high pass filtering the frequency-modulated luminance signal of step (d) before accomplishing step (q);

(s) low pass filtering the baseband audio signal of step (d);

(t) band pass filtering the frequency converted chrominance signal of step (d) before accomplishing step (h);

(u) suppressing the high frequency component of the frequency-modulated luminance signal of step (q) that was emphasized in step (k) subsequent to step (g);

(v) low pass filtering the frequency demodulated luminance signal of step (g) before accomplishing step (i); and

(w) band pass filtering the frequency converted chrominance signal of step (h) before accomplishing step (i).

8. The method as claimed in claim 3, wherein the low frequency carrier of step (b) is within a frequency range of 1 to 10 MHz.

9. An apparatus for transmitting and receiving multiplexed audio-video signals through a pair of telephone communication conductors by multiplexing a baseband audio signal and a video signal, comprising:

a transmitter including,

first separating means for separating an original signal into a luminance signal and a chrominance signal,

first modulating means for modulating the separated luminance signal with a low-frequency carrier,

first converting means for converting the separated chrominance signal to a frequency lower than its original frequency,

multiplexing means, operatively connected to said first converting means and said modulating means, for multiplexing the baseband audio signals the frequency-modulated luminance signal, and the frequency-converted chrominance signal by frequency division, and

transmitting means, connected to said multiplexing means, for transmitting the multiplexed signal; and

a receiver including,

second separating means operatively connected to said transmitting means for separating the transmitted signal into a baseband audio, a frequency modulated luminance signal, and a frequency converted chrominance signal,

demodulating means, operatively connected to said second separating means, for frequency demodulating the frequency-modulated luminance signal,

second converting means, operatively connected to said separating means, for converting the frequency-converted chrominance signal to its original frequency, and

combining means, connected to said demodulating means and said second converting means, for combining the signals to obtain the original video signal.

10. The apparatus as claimed in claim 9, further comprising:

second modulating means, connected to said first converting means, for modulating the chrominance signal prior to converting said chrominance signal; and

pre-emphasizing means, connected to said first modulating means, for pre-emphasizing the luminance signal prior to modulating said luminance signal, by emphasizing a high-frequency component of the luminance signal.

11. The apparatus as claimed in claim 10, further comprising

first low pass filtering means, connected to said pre-emphasizing means, for low pass filtering the luminance signal prior to pre-emphasizing of said luminance signal;

band pass filter means, connected to said separating means, for low band filtering the chroninance signal;

high pass filtering means, connected to said first modulating means for high pass filtering the frequency modulated luminance signal;

said second converting means band pass filtering the frequency-modulated chrominance signal to convert said chrominance signal to a lower frequency signal; and

second low pass filtering means, connected to said multiplexing means, for low pass filtering of the baseband audio signal prior to said multiplexing means.

12. The apparatus as claimed in claim 9, wherein the apparatus further comprises:

limiting means, connected to said second separating means, for removing an amplitude component of the frequency modulated luminance signal.

13. The apparatus as claimed in claim 12, wherein the apparatus further comprises:

high pass filtering means, connected to said second separating means, for high pass filtering the frequency-modulated luminance signal;

first low pass filtering means, connected to said second separating means, for low pass filtering the baseband audio signal

first band pass filtering means for band pass filtering the frequency converted chrominance signal

supressing means, connected to said demodulating means, for suppressing the high frequency component of the frequency-modulated luminance signal that was emphasized, subsequent to said luminance signal being demodulated;

second low pass filtering means, connected to said demodulating means, for low pass filtering the frequency demodulated luminance signal; and

second band pass filtering means, connected to said second converting means, for band pass filtering the frequency converted chrominance signal.

14. The apparatus as claimed in claim 9, wherein the low-frequency carrier of the first modulating means is within a frequency range of 1 to 10 MHz.

15. An apparatus for transmitting and receiving multiplexed audio-video signals between the two sets of transmitters/receivers, one transmitter/receiver set at each of a first and second station, by a pair of telephone communication cables, by multiplexing baseband audio signals and video signals, the baseband audio signals being bidirectional, comprising:

first frequency modulating means for frequency modulating the video signals at said first station with a first low frequency carrier;

first multiplexing means, operatively connected to said first frequency modulating means, for multiplexing said first frequency-modulated video signal with baseband audio signals at said first station;

second frequency modulating means for frequency modulating the video signal of said second station with a second low frequency carrier, different from said first low frequency carrier;

second multiplexing means, operatively connected to said second frequency modulating means, for multiplexing frequency-modulated video signal with baseband audio signals at said second station such that said multiplexed signals at each of said first and second stations both operate at different frequencies;

first and second transmitting means for simultaneously transmitting each of the multiplexed signals through the pair of telephone communication cables in a bidirectional manner;

first and second separating means for separating each of the multiplexed signals into audio signals and frequency-modulated video signals at each of said first and second stations respectively;

first and second limiting means, connected to said first and second separating means, respectively, for removing an amplitude component from each of the separated frequency-modulated video signals; and

first and second frequency demodulating means, connected to said first and second limiting means, respectively, for frequency demodulating each of the frequency modulated video signals, thereby allowing bidirectional transmission of the audio and video signals.