CA2182002A1 - Telecommunication system for transmitting full motion video - Google Patents

Abstract

A telecommunication system (10) is provided allowing the transmission of full motion color video, voice and data signal over a twisted pair of wires currently utilized only for voice and data communication. The signal is transmitted over a twisted pair link (16) as a broadband signal up to a distance of six thousand feet. The broadband signal received from the twisted pair link (16) is amplified and an impedance proportional to the impedance of the twisted pair link (16) and vectorially opposite thereto is impressed thereon. A unity gain is achieved whereby the signal degrading effects of the impedance of the twisted pair link (16) are reversed result in in the accurate reproduction of a video signal over significant lengths of the twisted pair link (16). Moreover, the compensation for twisted pair impedance allows accurate reproduction of broadband signal, a plurality of different video, telephone and data signals can be multiplexed together and transmitted simultaneously over the same twisted pair link (16).

Description

W095120287 2 t 8 2 0~ PCTtUS94/00433 ~r~r ~C,~, I ,rIoN SYSTE~ FOR TRAN~r FULL ~OTION VIDEO
.

,~pEcIFI~IoN
RAf`~(:Rn~ND OF TFIE INVENTION
DescriDtion of the Prior ~rt The present invention is a system for transmitting multiple communication 8ignals, i ncl1l~i ng at least one video signal, simultaneously over a link formed of a twisted pair of telephone wires.
Field of the Invention In conventional telPc i cation systems the transmission of full motion video images has heretofore been possible only over communication links especially adapted for broadband transmission, as contrasted with the bandwidth of signals employed in the transmission of telephone communic~tion~. The transmission of voice signals in telephone communications requires a bandwidth of about 4 kilohertz. This bandwidth will a~- -u'ate frequ~ncipc within the range of the human voice and the frequencies of dial and pulse code tones used for establishing connections.
To meet the reguirement for providing telephone service to communities throughout this country and throughout the world an inirastructure oi telephone lines has been established from telephone central ofiices to subscriber locations. In many countries Wo 95/20287 PCTiUS94/00433 2 ~ 82002 ;nclufl;ng this country such telephone lines are formed of lengths of twisted pairs of insulated copper wires of 16, 22, 24 or 26 gauge (AWG). Incalculable lengths of such twisted pairs of telephone wires have been installed by suspension from telephone poles and in buried conduits to link subscriber locations to telepllone central offices, which in turn are linked throughout the country and throughout the world by telephone communications networks.
Due to the ;~red~nce of a link formed of a twisted pair of telephone wires there is always an attenuation of the electrical n;c~tion signals transmitted over these wires. The extent of this attenuation depends upon the length of the twisted pair link. That i8, the longer the length of the twisted pair link the greater will be the total ~re~ nce between the central office and the subscriber's handset .
It is desirable in conventional telephone systems to create a uniformity in the attenuation of a signal from a subscriber location 80 that all of the telephone signals reaching a central office can be uniformly amplified and processed through the same type of common carrier equipment. The attenuation in a conventional link formed of a twisted pair of telephone wires below a prescribed frequency can be reduced and the lost frequency characteristic made nearly flat, by in~erting series inductance periodically. This practice of Wo gs/20287 2 1 8 2 ~ 0 2 PCT/US94/00433 inserting inductance periodically is termed loading.
It has been conventional practice to load twisted pairs of telephone wires at intervals of six th~lq~n~l feet where the wires are designed to conduct frequencies of from 0 to 4 kilohertz. The loading coils are normally located in manholes and in elevated equipment boxes on tr l~ph~n~ poles. The conventional loading practice provides a relatively uniform signal level at telephone central offices from subscriber locations located at varying distances from the central offices.
While conventional telephone lines formed of twisted p2irs of wire are s~ hle for the transmission of voice communications between telephone handsets and also for data communications, such as between computers and facsimile r~rhin~c~ the trannmiqsion of video signals over conventional telephone lines inr~ ing twisted pair links has heretofore been impractical.
Unlike voice and data - nications which require a bandwidth of only about 4 kilohertz, the transmission of full motion video signals, such as television signals, requires a bandwidth of a minimum of 4. 5 megahertz. In telephone communications systems in this country the Federal Communications Commission requires telephone - n i cation carriers to allocate a bandwidth of 6 megahertz for the transmission of television signals. In other countries, such as in ~urope, a bandwidth of 7.5 megahertz is required.
The reason that a video signal re~uires a Wo 9s/20287 PC rluS94/00433 2 ~ 82002 bandwidth far greater than a voice signal is because of the multitude of points which must be 3canned in a horizontal scanning raster in order to convey a video picture. At the end of each scan a blanking pulse is generated with respect to the video information to be reproduced, and a line synchronizing pulse of a polarity opposite to the video information is generated during this blanking pulse. The line pulses synchronize the individual horizontal scanning lines.
Similarly, it is necessary to synchronize the field or vertical scans. This is done by another pulse train which occurs during the f ield retrace time .
In conventional full motion or "fast scan"
television transmission, the time interval from the start of one horizontal line to the next is 63 . 5 microsecr~nrl~. Each complete frame consists of two interlaced fields. The frame rate is 30 per second and there are 525 scanning lines per frame, of which about 93~ are visible because of the 1088 of time during the field blanking pul3e. To make a horizontal resolution approximately equal to a vertical resolution, a minimum bandwidth of about 4 . 5 megahertz is required . This frequency range and above will hereinafter be referred to as a broadband frequency spectrum, as contrasted with the narrow band frequency spectrum of 4 kilohertz which is employed in voice and data transmission.
Conventional lines currently employed in the infrastructure of telephone - ications have -Wo 95/20287 2 1 8 2 0 0 2 PCT~US94100433 .

heretofore been considered unsatisfactory for the transmission of video signals due to the degradation which video signals experience in passing over a conventional twisted pair of telephone wires. For a length of more than about one tho~lCAn~l feet, the horizontal sync pulses of a video signal lose their definition and become intermixed with the video data.
As a consequence, the receiver cannot distinguish between horizontal scan lines. Also, the portions of the signals near the upper and lower ends of the frequency band experience far greater degradation than the portions of the signals near the middle of the band. Since color information is transmitted at the upper end of the frequency band of a video signal, color quickly becomes lost in transmission of a video signal over links inr~ iing conventional twisted pairs of telephone wires. Thus, the transmission of full motion televised video signals, especially color video, has heretofore required broadband carrier $acilities.
The eYisting infrastructure of telephone communications lines has heretofore been considered unacceptable for the trAn~miRsi~>n of full motion video signals.
SnMMA~V 0~ T~E INVENTION
A primary object of the present invention is to provide a telec nication system employing the medium of a link of one or more lengths of twisted pairs of telephone wires for use in transmitting full motion video signals. The telecommunication system of the Wo 95/20287 PCTIUSg4/00433 2 ~ 82302 invention thereby allows a television camera to transmit a Yideo signal over a conventional twisted pair of telephone wires.
By providing a system for transmitting video signals over communication links employing conventional twisted pairs of t~lerhnne wires, the invention allows video signals to be transmitted over the existing infrastructure of telephone communication lines that are in place and operating throughout virtually all population centers. The invention dispenses with the need for special purpose broadband carrier facilities to be routed into a building structure in order to transmit a video signal from that location.
In one broad aspect the present invention may be considered to be a telephone communication circuit for transmitting video signals comprising: video signal initiation means for providing a video signal of at least 4.5 megahertz bandwidth, line driver means coupled to the video signal initiation means to amplify the video signal, a link formed of a twisted pair of unloaded telephone wires having opposite ends one of which is coupled to receive the amplif ied video signal, symmetrical video transformer means coupled to the other o~ the ends of the twisted pair link to receive and amplify the video signal, correcting amplifier means coupled to receive the video signal from the symmetrical video transformer and to impress thereon an i ~r~d~ e proportional to the impedance in the twisted Wo gs/20287 2 1 8 2 0 0 2 PCr/US94100433 pair link and in vector opposition thereto to thereby correct the video signal for imred~nce degradation in said twisted pair link, and a video receiver coupled to the correcting amplifier means for receiving the corrected video signal.
In another broad aspect the invention may be considered to be an improvement in a telephone ~ nicfltion circuit includ;ng a twisted pair link comprised of an unloaded twisted pair of wires of a known length and having first and gecond ends. The improvement of the invention is comprised of a video signal provision means for providing a video signal having a bandwidth of at least 4.5 megahertz, line driver means interposed between the video signal provision means and the first end of the twisted pair link to amplify the video signal, whereby the twisted pair link exhibits a known i ~'~nce thereto, unity gain amplif ication means coupled to the second end of said twisted pair link to reproduce the video signal wi~h a ~ ~ating i -d~nce impressed thereon that is proportional and opposite to the known i~r~nce, and a video receiver coupled to receive the video signal with the - ~ting impedance impressed thereon.
The principle of operation of the invention requires the pairs of telephone wires in the twisted pair link to be unloaded. This is easily done where the pair of wires is no greater than six thousand feet in length, since loads on such wires are normally Woss/202s7 Pcr/uss4/00433 2 1 820~2 imposed only at the subscriber location and at the telephone central office. Any loading on the twisted pair of telephone wires must be removed in order for the invention to function properly. If the twisted pair link is greater than 5iX i-hollcAn~ feet, line amplifiers have to be employed at intervals of no greater than six thousand feet. The twisted pair link may either be formed of a single twisted pair of wires extending between two stations, the aggregate length of subscriber lines connected between 6ubscriber locations and a common central office, or the aggregate length of subscriber lines connected between subscriber loca~ion~
and different central offices.
In the absence of loading, a conventional twisted pair of telephone wires will eYert a known il~rpdAnce on a video signal transmitted over those wires. Since impedance i5 a transmission factor with a vector, it is possible to impose a corrP~pont'l~ng, opposite i ~AnCe on the received signal before the signal is passed to the video receiver for display. The effects of imredAnce on the video signal are thereby reversed.
Therefore, although the horizontal sync pulses of a video signal are degraded, as are the information bearing portions of the video signal at the upper and lower ends of the video signal band, the corrective imre~Ance impressed on the received video signal has the greatest corrective effect on these portions oi the video signal. As a consequence, once the opposing Wo 95120287 2 1 8 2 0 0 2 Pcrlus94/00433 impedance has been impressed upon the received video signal, the signal i8 quite accurately reconstructed to its original form that it had upon its arrival at the transmitting end of the twisted pair of telephone wires .
Because it is pos3ible to fully reconstruct a video signal, a conventional telephone twisted pair link is no longer limited to the narrow 4 kilohertz frequency band of voice and data transmission. To the contrary, broadband or wide band signals may be transmitted over conventional twisted pairs of telephone ~ires. The video signal transmitted over the tele~ nication circuit of the invention preferably is provided by a video signal initiation means that has a bandwidth of at least about 6 megahertz. Thus, a video signal conforming to the ~ederal Communication Commission television channel requirements for monochrome and color television transmission may be transmitted according to the invention.
The correcting amplifier means which impresses the corrective imp~ dAnre upon the received video signal is preferably comprised of a receive signal emitter follower amplification circuit and resistor-capacitor combinations which are selectively and alternatively strapped into the receive signal emitter ollower amplification circuit as determined by the length of the twisted pair link. The correcting amplifier means i8 also comprised of phase adjustment means ~or wo 95/20287 PcrlUS94/00433 applying a phase adjustment to the video signal. This phase adjustment means is formed of a phase adjustment amplif ier circuit and resistor-capacitor-inductor combinations which are selectively and alternatively strapped into the phase adjustment amplifier circuit as determined by the length of the twisted pair link.
The line driver means is preferably comprised of a gain selection means including a transmit signal emitter follower amplification circuit and resistor-capacitor combinations which are selectively and alternatively strapped into the transmit signal emitter follower Am~l~fica~ion circuit as determined by the length of the twisted pair link. sy providing the line driver means with selected resistor-capacitor combinations, the system can be adjusted so that the video signal is degraded more uniformly across its bandwidth as it is transmitted through the twisted pair of telephone wires, and is not excessively degraded at the upper and lower ends of the video signal frequency band. It thus is more easily corrected and reconstructed by the symmetrical video transformer means and the correcting amplif ier means .
To take further advantage of the capability of broadband transmission now possible utilizing conventional twisted pair links according to the invention, preferred ofl;r?rts of the invention involve not only the transmission of a single video signal over a conventional twisted pair link, but also Wo 95120287 PCr/US94/00~33 21 8200~

the multiplexing of a plurality of signals over a conventional twisted pair link. The plurality of signals are frequency modulated together at the transmitting end and demodulated at the receiving end of the tele~ ication circuit. Indeed, a plurality of video signals, a plurality of voice signals, a plurality of data signals, and various combinations o~
video, voice and data signals can be transmitted over a single conventional twisted pair link comprised of telephone wires designed ~or use on an ordinary telephone handset using multiplexing techniques.
In such a multichannel system according to the invention the t~ ication circuit is comprised of not only a video signal initiation means but also at least one voice band signal initiation means for providing a voice band signal. Such a signal has a bandwidth of about 4 kilohertz. The system is further provided with multiplesing means coupled to receive the video signal from the video signal initiation means and the voice band signal from the voice band signal initiation means and to transmit the video signal and the voice band signal simultaneously through the line driver means and over the twisted pair link. In addition to the video receiver a voice band receiver is coupled to the correcting amplifier means for receiving the voice band signal.
The system of the invention may be utilized to transmit signals multiplexed together over a 10 megahertz bandwidth. Thus, for example, a video signal may be multiplexed together with a full duplex telephone voice signal of 4 kilohertz and further addltional full duplex data signals, voice signals, or a com~ination of data and voice signals. Noreover, a plurality of video signals can be multipleYed together and transmitted utilizing the system of the invention.
Indeed, by utilizing quadrature amplitude modulation techniques a total of four different video signals can be multiplexed together and transmitted over a single twisted pair link simultaneously.
The invention may be described with greater clarity and particularity with reference to the a- ~ - ying drawings.
D~RTPTION OF T~ DRAWINGS
Fig. 1 is a block diagram of one ~ t of a full duplex, multiplesed t~l e~ ation system constructed according to the invention.
Fig. 2 is a block diagram of one of the transmitting t~rmin~1c at one of the stations in the telecommunication system of Fig. 1.
Fig. 3 i5 a frequency diagram showing the different signals as modulated by the transmitting terminal of Fig. 2.
Fig. 4 is a block diagram of one of the receiving terminals at one of the stations in the tel~ -- i c~tion system of Fig. 1.
Fig. 5 is a schematic diagram of the direct wo 9s/20287 2 1 8 2 0 0 2 PCr/USs4/00433 current voltage supply for both the transmitting terminal of Fig. 2 and the receiving terminal of Fig.
4.
Fig. 6 is a schematic diagram of a double bAlAn~ed mixing circuit employed in both the transmitting terminal of Fig. 2 and the receiving terminal of Fig. 4.
Fig. 7 is a sc8 tiC diagram of an amplifier oscillator circuit employed in both the transmitting terminal of Fig. 2 and the receiving tPrminAl of Fig.
4.
Fig. 8 is a 8~ tic diagram of a bAnflpAcs filter circuit employed in both the transmitting tPrminAl of Fig. 2 and the receiving tPrminAl of Fig.
4.
Fig. 9 is a schematic diagram of a notch filter circuit employed in both the transmitting terminal of Fig. 2 and the receiving t~rminAl of Fig. 4.
Fig. 10 is a schematic diagram of an oscillator circuit employed in both the transmitting circuit of Fig. 2 and the receiving circuit of Fig. 4.
Fig. 11 is a sc~ tic diagram of a broadband amplifier circuit employed in the transmitting terminals of the t~le~ nication system of Fig. 1.
Figs. 12a and 12b are schematic diagrams of the line driver circuit employed in the transmitting tPrminAlc of the telecommunication system of Fig. 1.
Figs. 13a and 13b are 8chematic diagrams of the wo 9~/20287 PC r/uss4l00433 symmetrical video transformer circuit employed in the receiYing terminals of the telec-- nication system of Fig. 1.
Figs. 14a and 14b are schematic diagrams of the correcting amplifier circuit employed in the receiving terminals of the telP- ~ ; c~tion system of Fig. 1.
Fig. 15 is a block diagram of a variation of the telecommunication system of Fig. 1.
~ESCRIPTION OF T~E EMR~7nTMF~
Fig. 1 illustrates a telec nication ~ystem indicated generally at 10. The telec- ~ication aystem 10 extends between a pair of stations 12 and 14, each having a transceiver, which are coupled together by twisted pair links 16 each comprised of an unloaded twisted pair of telephone wires.

stati~7nc At each of the stations 12 and 14 of the telecommunication system 10 there is a video signal source, indicated diagrammatically as a video camera 18 and also a video receiver indicated diagrammatically aæ
a television receiver or monitor 20. The video signal source 18 has a signal frequency bandwidth of at least 4.5 megahertz and preferably at least 6.0 megahertz.
Each of the stations 12 and 14 is further comprised of a multiplexing unit 22 having a frequency modulating circuit 24 and a frequency demodulating circuit 26. The video signal source 18 is connected through the frequency modulating circuit 24 of the Wo 9s/20287 2 1 8 2 ~ 0 2 PCrlUSs4/00433 multiplexing unit 22 to a broadband amplification circuit 28. The broadband amplification circuit 28 is coupled to the video signal source 18 to receive the signal therefrom to produce an amplified signal. The broadb~nd amplification circuit 28 is illustrated schematically in Fig. 11.
The llnloA~ed twisted pair links 16 each have a length no greater than gix thousand feet and a known i~rPdAnce. The twisted pair links 16 are coupled to receive the amplified broadband signal from the broadband amplification circuit 28. The transmitters of each of the stations 12 and 14 are also each equipped with a line driver circuit 19 having circuit portions 218 and 220 which are illustrated respectively in schematic form in Figs. 12a and 12b.
The receivers in each of the stations 12 and 14 are each provided with a symmetrical video transformer circuit 30 that is coupled to the twisted pair of telephone wires 16 to receive and amplify the broadband signal therefrom. sach symmetrical video circuit 30 includes circuit portions 250 and 252 which are illustrated in Figs 13a and 13b respectively. Each of the stations 12 and 14 also includes a correcting amplifier means in the form of a correcting amplifier circuit 32. The correcting amplifier circuit 32 has circuit portions 258 and 260 which are respectively illustrated in Figs 14a and 14b.
The correcting amplifier circuit 32 is coupled to _ _ _ _ _ _ _ _ _, .

the symmetrical video transformer circuit 30 to provide an offsetting impedance to the broadband signal. This offsetting imr~A~n,-e is proportional and in opposition to the known irreA~n~e of the twisted pair link 16.
The offsetting 1m"~n~e thereby negates the effect of the known ~ eA~nce of the twisted pair 16 on the broadband signal that passes over the twisted pair 16.
The video receiver 20 is coupled to receive the broadband signal from the correcting amplifier circuit 32 through the demodulating circuit 26 to eYtract a video signal therefrom.
As illustrated in Figs. 1-4, the stations 12 and 14 of the telec~- ication system 10 are comprised of not only circuitry for transmitting and receiving a video signal over a twisted pai~ link 16, but are each further comprised of additional signal sources for providing additional tele~ 1c~tion signals. These signal sources are indicated diagrammatically as a telephone handset 34 and four data transmission sources, indicated diagrammatically as the data transmitting modules 36, 38, 40 and 42 of computer modems. 5ach of the stations 12 and 14 also is provided with a telephone handset 34' and data receiving modules 36', 38', 40' and 42' which are respectively coupled to the telephone 34 and the data transmitting modules 36, 38, 40 and 42 of the other station through the multipleYing units 22.
The frequency modulating circuit 24 is coupled to Wo 95/20287 2 1 8 2 0 0 2 PCT/US94100433 receive the signals from the signal sourceS 18 and 34-42 and to modulate those signals. The broadband ampliiier circuit 28 is coupled to the frequency modulating circuit 24 to receive the modulated signals therefrom and to pass the amplified signals to the line ~river circuit 19. The demodulating circuit 26 is coupled to the symmetrical video transformer 30 and to the correcting amplifier 32 to receive the broadband signal of Fig. 3 therefrom. The demodulating circuit 26 ~7e ' 7 ~tes the broadband signal to separately reproduce the video signal and transmit it to a video receiver 20 and to separately reproduce each of the additional signals and transmit them to corre~p~n~7ing nic~tion receivers 34', 36', 38', 40' and 42'.
The communication receiver 34 ' is a conventional telephone handset, while the receivers 34', 36', 38', 40 ' and 42 ' are all data receiving modules of computer data modems.
DC Power SUI~1Y
The modulating circuit 24 of the stations 12 and 14 are identical to each other and are of the type depicted in block diagram form in Fig. 2. Power is supplied to both the modulating circuit 24 and the demodulatLng circuit 26 at each station by a common power supply which is illustrated schematically in Fig.
5. The direct current power supply is derived from either a 110 or 220 volt alternating current power source. The alternating current input is provided on _ _ _ _ _ _ _ _ _ wo 9s/20287 PC r/uS94/00433 ~

either lines 162 and 164 or lines 162 and 166, dPp~; ng upon whether the available alternating current power supply is 110 or 220 volts. The alternating current supply is provided as an input to power transformer 168, the secondary of which is connected to a rectifier circuit 170. The diodes Dl-D4 of the rectifier circuit 170 are model IN4003 diodes.
The rectified power output is provided to a model LP
2400, 24 volt direct current regulator. The power supply circuit also employs two 101 microfarad capacitors 174; two 1 microfarad capacitors 176; and two 2200 microfarad capacitors 1~8. A 2 microhenry inductor 180 provides the regulated direct current power supply to the modulating circuit 24 and the d ~ ting circuit 26 as the B~ voltage through a diode 182.
Mll 1 ti~lex Sv6tem The video signal generating source 18 of Fig. 1 produces a composite video signal 43 which has a video channel output 44 and an audio channel output 46 that appear on separate BNC connectors 48, as indicated in Fig. 2. The composite video signal 43 is from 0.7 to 1. 77 volts, peak to peak with a 6 megahertz bandwidth and 75 ohms imre~nce. The video component 44 and the audio component 46 of the video signal 43 are mixed together in a mixing circuit 50. The individual circuit modules of the I ' 1 i~ting circuit 24 and the demodulating circuit 26 are illustrated in Figs. 6-10.

Wo 95120287 PC rlUSs41~433 2 1 82~02 .

The mixing circuit 50 is depicted schematically in Fig.
6 and is used to mix the audio and video components 44 and 46 of the video signal into a composite signal of 6 megahertz bandwidth. The mixer circuit 50 transmits that signal to an amplifier circuit 52 which is illustrated 5~h tiCAl ly in Fig. 7. The amplified output from the amplifier 52 is directed to a ~An/irAR5 filter 64 which is illustrated schematically in Fig. 8.
The t~An~rAcs filter 64 passes an output of 0 to 8 megahertz bandwidth. This signal appears at 55 in Figs. 2 and 3 and is coupled to line 56 which leads to the broadband amplifier 28 of Fig. 1, that is illustrated sc~ ~;CA1 ly in Fig. 11.
The telephone signal initiating device 34 is a conventional RJll full duplex telephone handset. The telephone signal from the handset 34 is passed as an additional signal input on line 58 to a 4 kilohertz bAn~lpAR~ filter 60 of the type illustrated schematically in Fig. 9. From the bAnllrAC5 filter 60 the telephone signal i8 directed to a mixer circuit 50 of the same type employed to mix the audio and video components 44 and 46 of the video input signal 43.
~owever, the miYer circuit 50 which receives the filtered telephone signal is used to modulate the telephone signal with a subcarrier frequency generated by an oscillator circuit 62, depicted schematically in Fig. 10. The subcarrier frequency generated by the oscillator circuit 62 for the telephone c ica~ n signal is a signal of 8.06 megahertz frequency. Both the mixer circuit 50 and the oscillator circuit 62 are powered by the B+ direct current voltage supply derived from the power supply circuit depicted schematically in Fig. S.
The output of the miser 50 that amplifies the telephone input signal from the telephone handset 34 is directed to a b~n~r~CC filter circuit 64 of the type depicted schematically in Fig. 8. The output of the bAnt?r51CC filter 64 is directed to another amplifier circuit 52 of the type depicted in Fig. 7. The amplifier circuit 52 which is used to amplify the telephone signal has the same circuit configuration as the amplifier circuit 52 employed to ampli~y the video signal, but with components of different values so as to produce an amplified output in a different band range .
The output from the amplifier circuit 52 which amplifies the telephone signal is directed to another b~n~r~cs filter 60 of the type depicted in Fig. 9. The filtered and amplified telephone signal that was first originated at the telephone handset 34 is passed as a modulated signal 66 lying in the frequency range between 8 . 0 and 8 .10 megahertz. The modulated telephone signal 66 is combined with the filtered and amplified video signal 55 and passes on line 56 to the broadband amplifier circuit 28, depicted schematically in Fig. 11.

Wo 95l20287 PCTIUS94/00433 2 1 820~2 A further additional signal initiating means may be the transmitting portion 36 of an RS 232 full dupleY
serial input data modem. The input portion 36 of the P~s 232 modem produces a data signal 68 having a 4 kilohertz bandwidth. The additional data signal 68 is transmitted to a b~n~lp~s filter circuit 60 of the type depicted in Fig. 9 to eliminate ambient 60 cycle harmonics and other noise. The filtered data signal is then transmitted to a miYer circuit 50 of the type depicted in Fig. 6, where it is miYed with a subcarrier frequency of 8.26 megahertz by an osc~ tor circuit 62 of the type depicted in Fig. 10. The modulated data signal is then passed to a broadband filter circuit 64 of the type depicted in Fig. 8, and then to an amplifier circuit 52 of tlle type depicted in Fig. 7.
The amplified data signal is then passed to a notch filter circuit 60 of the type depicted in Fig. 9. The filtered and amplified data signal 70 lies in a frequency band between 8.2 and 8.4 megahertz.
The other additional data signals are likewise generated by the transmitting portions of RS 232 full duplex data modems, indicated at 38, 40 and 42. These transmitting modem portions generate additional data signals indicated respectively at 72, 74 and 76. These data signals 72, 74 and 76 are processed precisely in the same manner as the data signal 68, with the exception that the subcarrier frequency generated by the oscillator circuit 62 for each data signal is different. The filtered and amplified data signal 78 lies in a frequency band between 8.6 and 8.7 megahertz.
The filtered and amplified data signal 80 lies in a frequency band between about 8.9 and 9 megahertz, while the r- ' 1 atPA data signal 82 lies in a frequency band of between about 9 and 10 megahertz.
When the modulated signals 55, 66, 70, 78, 80 and 82 leave the modulating circuit 24, they lie within a broad 10 megahertz bandwidth, as indicated in Eig. 3.
The composite signal on line 56 is then passed to the broadband amplification circuit 28 of Fig. 11.
Milrer Circuit Fig. 6 schematically illustrates the mixer circuit 50. The mixer circuit 50 is employed in the processing of the video signal 43 to mix the audio and video signal components 44 and 46. In the processing of the video signal 43 the audio ~ t 44 is passed as a shielded input on line 84 to the coil 86 of a transformer circuit. The video input 46 is passed as a shielded input on line 88 to the center of a transformer coil 90. The transformer coil 90 is coupled to a rectifier circuit 92, the output of which is connected to a transformer coil 94, the center of which is grounded. The composite mixed output of audio and video appears on the transformer coil 96 and is passed as an output signal on line 98.
The same mixing circuit 50 is employed to mix the telephone and data signals with the subcarrier ~W095120287 2182aO2PCrlUS94100433 frequency generated by the oscillator circuit 62 of Fig. 10. In the processing of the telephone and data signals the voice or data signal is provided as a shielded input on line 84 while the carrier frequency from the oscillator circuit 62 is provided as a shielded input on line 88. The data signal, modulated by the carrier frequency from the oscillator circuit 62 ~ppears as an output on line 98.
1 if ier The modulating circuit 24 also employs a separate amplifier circuit 52 for each of the video, telephone and data signals. The input to the amplifier circuit 52 appears on line 112 and is passed through a capacitor 114. In the circuitry for amplifying the video signal the capacitor 114 is a .1 microfarad capacitor, while in the circuitry for amplifying the voice and data signals the value of the capacitor 114 is .22 microfarads. B+ voltage is provided on line 116 from the power supply circuit of Fig. 5. The amplifier circuit 52 also includes a 56R ohm resistor 118, a 15K
ohm resistor 120 and a 68R ohm resistor 122. An NPN
transistor 124 provides an amplified common emitter output on line 126.
Oscillator The oscillator circuit 62 is depicted in detail in Fig. 10. The oscillator circuit 62 employs a model 2~489 field effect transistor 100, a 16 picofarad caeacitor 102, and resistors 104, 106 and 108 having WO 95/20287 PCT/US94100433 ~

values of 470 ohms, 27R ohms and 330 ohms, respectively. The oscillator output appears on line 110, which is connected to the input line 88 of the double t~l~nc~ mixer circuit 50 of Fig. 6 for each of the telephone and voice signal modulating circuit paths .
R;lntln;lRc Filter Each modulating circuit 24 also includes a passive bandpass filter 64 for each of the video, telephone and date signals. The bandpass filter circuit 64 is illustrated schematically in Fig. 8. The input appears on line 128. The broadband filter circuit 64 includes a tank circuit having an inductor 130 and a variable capacitor 132 connected in parallel from ground to the signal path. The inductor 130 has a value of 27 microhenrys while the capacitor 132 varies between 0 and 80 picofarads. The tank circuit output is coupled between two capacitors 134 of 22 picofarads each, which together are coupled in parallel with a 47 picofarad capacitor 136 between the signal input on line 128 and the filtered signal output on line 138.
The output line 138 from the bandpass filter circuit 64 in the video signal modulating circuit carries the amplified and filtered video signal 43 from the video camera 18 as the mixed and amplified video signal 55. The b~ndr~cs filter circuit 64 may be tuned to provide a frequency output 6 megahertz in bandwidth for tllose video systems where video channels are ~ W09s/20287 2 1 82~22 Pcrlusg4/0o433 allocated a 6 megahertz bandwidth. Alternatively, the b~nflpAcs filter 64 may be tuned to provide an output of 7.5 megahertz bandwidth for those carrier systems in which video channels are allocated a 7 . 5 megahertz bandwidth output. The bAnflrl~s filters 64 employed in filtering the telephone and data signals, on the other hand, are tuned to provide an output having a bandwidth of between 1 and 2 megahertz for each telephone signal 58 and each data signal 68, 70, 72, 74 and 76.
Notch Filter Each modulating circuit 24 also filters each of the narrow frequency band telephone and data signals from the handset 34 and from the data modem transmitter section 36-42 through notch filter circuits 60 of the type depicted in detail in Fig. 9. The input signal to each notch filter circuit 60 appears on line 140 as the negative input to an operational amplifier 142. The notch filter circuit 60 also includes resistors 144, each having a value of 3.3 R ohms, resistors 146, each having a value of lOR ohms, a resistor 148 having a value of 68R ohms, and capacitors 150 of . 33 microfarads each. The output of operational amplifier 142 is directed as the negative input to another operational amplifier 152, which is coupled in a loop to operational amplifier 154. The output of operational amplifier 152 is also connected to the negative input of operational amplifier 156. The output of operational amplifier 142 is connected also -Wo 95/20287 PC r/USs4l00433 ~

to the negative input of an operational amplifier 158.
The operational amplifiers 142, 144, 152, 156 and 158 are all IC components, model NC4301. The filtered output of the notch filter circuit 60 appears on line 160 .
The wave form of the composite multiplexed broadband signal output produced by each modulating circuit 24 i5 depicted diagrammatically in Fig. 3. The video signal indicated at 55 may be either 6 megahertz or 7. 5 ~egahertz in bandwidth. The telephone signal 66 lies in a bandwidth between 8 and 8.10 megahertz. The data signal 70 lies in the bandwidth between 8 . 2 and 8.4 megahertz. Data signal 78 lies in the 8.6 to 8.7 megahertz band, while data signal 80 has a bandwidth between 8.9 and 9 megahertz. Data signal 82 lies in a bandwidth between 9 and 10 megahertz.

~Iro;l-~h; n~ Z~mnlif ier The broadband amplification circuit 28 depicted in Fig. 11 is interposed between the camera 18 that provides the video signal 43 and the first end 15 of the twisted pair of telephone wires 16 to amplify the multiplexed video signal 43, as well as the multiplexed telephone and data signals. The broadband amplification circuit 28 receives the amplified and modulated video, telephone and data signals from their respective sources and produces an amplified broadband signal output.
The broadband amplifier circuit 28 includes a -W095/20287 2 l ~ 20 ~ 2 PCT/US94/00433 tank circuit having a 245 microhenry inductor 190 and a variable capacitor 192 that can be varied between 0 and 80 picofarads. The output of the tank circuit is connected between a pair of capacitors 134 which are coupled in parallel with capacitor 136. The tank circuit and the capacitors 134 and 136 filter the input ~ignal on line 56 to amplify only the desired 10 megahertz oandwidth and filter out ambient RF signals that are likely to be present in an environment of computers and video processing equipment.
The isolated 10 megahertz band output is passed to a capacitor 194 which serves as the input to a two stage amplifier. A model BC548 NPN tranBistor 196 provides the first stage of amplification. The emitter of transistor 196 is connected to a 15R ohm resistor 198 and to a 150 ohm resistor 200 at the base of a model BC324 PNP transistor 202 which serves to correct for i~ p~Ancpc~ The collector of transistor 202 is connected to a 1.5R ohm resistor 204 and the emitter receives B+ voltage through a lR ohm resistor 206.
The second stage of amplification is formed by transistors 208 ~nd 210 which are coupled together.
Both of the transistors 208 and 210 are model sC548 NPN
transistors. Two transistors are employed in parallel to handle the amount of current that is developed. The emitters of the transistors 208 and 210 are coupled to ground through resistors 212 and 204, respectively.
Resistor 212 has a value of 3.9K ohms. The output of _ _ _ _ _ .. . . _ . .. . .. _ _ _ . ..

wo 95/20287 PCTIUS94100433 21~20~)2 the second amplification stage is directed through a 75 ohm resistor 214 and appears as an output on line 216.
The broadband amplifier circuit 28 ensures that all portions of the spectrum of the input frequency on line 56 are linearly amplified in the output signal 216.
The signal amplitude of output signal 216 is thereby uniform.
r.i ne DriVer The output 216 of broadband amplifier circuit 28 is provided as an input to circuit portions 218 and 220 which together form the line driver circuit 19 and are depicted ~c~ ~iC:~l ly in Figs. 12a and 12b, respectively. The signal input line 216 to the line driver circuit 19 appears in Fig. 12a. The line driver circuitry of Figs. 12a and 12b is comprised of a gain selection means i nclQA i ng a transmit signal emitter follower amplification circuit and resistor-capacitor combinations which are selectively and alternatively strapped into the transmit signal emitter follower amplification circuit as determined by the length of the twisted pair link 16. The values of the resistors and capacitors are set forth in Table 1. The amplif ier, diode and transistor model designations are also set forth in Table 1.

TABL~ 1 CQml~onent Value/Desiqn2tiQn 12IC1 = 78~15CFAI
12D1 ~ IN 4003 12D2, 12D3, 12D4 = IN 4148 12D5 = BZX97A9V1 12D6 = BZX83C2V7 12D7 = BZX83C5V5 12D8 = BZX83C6V8 12C1, 12C5 = 0.22 microfarad, lO0 volts 12C2 - 10 m_CrOarad8, 35 volts 12C3 = 2.2 m_crofarads, 16 volts 12C4 - 22 m_crofarads, 15 volts 12C6 ~ 0.1 m crofarad, 63 volts 12C' ~ 1000 p_cofarads, 63 volts 12C~. = 22 m crofarads, 16 volts 12Cq e lO0 p_cofarads 12C' 0 - 68 p_cofarads 12C' 1 - 220 p_cofarads 12C_2 = 150 p_cofarads 12C13 ~ 6 p_cofarads _2C14 = ~70 P cofarads _2C15 = 00 P cofarads 2C16 = ~2 p_cofarads _2C17 ' J30 p_cofarads ~ 2C18 = ~ .2 m_crofarads, 16 volts _2C_9, 12C22 = _0 m_crofarads 3 volts _2C''O, 12C21 = 22 m_crofarads, 16 volts 2C_3 - 47 m_crofarads, 63 volts 2C~ 4, 12C25 = 10 m_crofarads, 35 volts ~ 2T_, 12T2 = BC558B
_2T~, 12T7 = BF311 _~T-- = BC558C
_~.T'~, 12T6, 12T10 = BC548B
_ T-, 12T9, 12T11 = BC338.405IE
_~T 2 = BC328 . 40SIE
_~R_ - 15 ohms ~ ~ R-, 12R5 = 82 ohms '-R, ~ 100+ ohms R4 = 130 ohms ~R6 = 22 ohms 12R7 = 22R ohms 12R8 = lOOg ohms 12R9, 12R13 = 10R ohms 12R10 = 1. 69 R+1~ ohms 12R11, 12R18, 12R19 = 1. 5R ohms 12R12 - 560 ohms 12R14 = 56 ohms 12R15 = 2R Ohm8 12R16, 12R23 = 2.2R ohms WO 95120287 PCTI[JS94/00433 2 1 820~Z

TARrF~ 1 ~Continued) r, -nent Val lle~D~cion~tion _2R17 = 100 ohms _'`R20 = 150 ohms ' _R21 = 5. 6R ohms _''R22 = 2 . 7R ohms l:R24, 12R27 = 681 _ 1~ ohms l''R25, 12R2g = 820 ohms _'`R26 = 180R ohms __R28, 12R36 = 680 ohms _:`R,0, 12R31, 12R34 - ' 8 _ 2~ ohms :2R,2, 12R33 = ''4 + 2~ ohms _2R,5 = _8 ohms ' 2R~7 = ' 2R ohms _2R38 = 1. 5R ohms 12R-9 = 18 ohms As illustrated in Figs. 12a and 12b there are a number of bridges provided initially in a normally open condition.
These bridges are in~icated at 12A, 12B, 12J, 12R, 12L, 12M
and at 12X, 12V, 12II, 12III, 12VI, 12Xl, 12Vl and 12IIl.
Contacts 12~, 12B, 12J, 12R, 12L, and 12N are selectively strapped by soldering, while contacts 12II, 12III, 12V, 12X, 12XI, 12Vl, 12VI, 12IIl, 12E, 12F, 12G and 12~ are plug-in bridges.
The selective strapping of the ~ridges determines which resistor-capacitor combinations are brought into the line driver circuit 19. To illustrate, the resistors 12R14 through 12R21 and 12R38 and the capacitors 12C9 through 12C16 may be selected in alternative combinations as determined by the plug-in bridge contacts 12X, 12V, 12II, 12Xl, 12Vl and 12IIl to change the gain of the amplif ier 12T3. The appropriate gain of amplifier 12T3 i5 dependent upon the length and impedance of the twisted pair link 16.
By selecting the appropriate resistor-capacitor combination, saturation of the transistor 12T3 is prevented, ........ . .. _ . _ .... .. ..... .... _ _ _ _ _ _ _ _ _ _ _ . . . .

WO 95120Z87 2 1 8 2 0 0 2 PCT/USg4100433 depending upon the frequency band to be transmitted. That is, the circuit configuration depicted in Figs. 12a and 12b is suitable for transmitting a bandwidth of from 6 to 10 megahertz as received from the output line 216 of the broadband amplifier circuit 28. Appropriate selection of the resistor-capacitor combinations is made depending upon the bandwidth, as well as upon the imre~Ance of the twisted pair link 16. The output of transistor 12T3 on line 230 is uniformly amplified over the frequency band selected and is provided to the amplification stages of transistors 12TS-12T12 in Fig. 12b.
~ rPRndiy A hereto sets forth exemplary soldered and plug-in contact connections which are strapped into the circuit as appropriate for different lengths and different gauges o~ wire for the twisted pair link 16, as indicated.
The conditions of the contacts for other lengths and gauges of twisted pair links is ascertained empirically.
From the line driver circuitry of Figs. 12a and 12b the amplifier outputs are connected to the first end 15 of the twisted pair of telephone wires 16. The telephone wires employed in the twisted pair links 16 are conventional in~-lAted copper wires of 16, 22, 24 or 26 gauge which are used throughout the national telephone network for supplying telephone service to subscriber locations from telephone company central offices. The twisted pair links 16 must be unloaded and may be of a length dependent upon the gauge of the wire employed. ~or example, a twisted pair link 16 with polyethylene insulation may be ue to 11,055 feet in length _ _ _ _ _ _ _ . _ . . .

wo 95/20287 PCr/US9410C433 if 19 gauge wire is employed. A twisted pair link 16 with polyethylene insulation may be up to 9,570 feet in length if 20 gauge wire is employed; up to 7,755 feet in length if 2~
gauge wire is employed; and up to 5,775 feet in length if 26 gauge wire is employed. Twisted pair links of even greater lengths may be utilized by ~-Y;mi z ing the efficiency of the components employed in the system.
S - ' r i ~ l Video Tr In c f o rme r At the second end 17 of each twisted pair link 16 the signal, incl~ ng the video signal originally provided at 43, appears as an input to the symmetrical video transformer circuit 30 having circuit portions depicted at 250 in Fig.
13a and at 252 in Fig. 13b. The input to the symmetrical video transformer circuit portion 250 in Fig. 13a is proYided on lines 254 and 256 from the second end 17 of the twisted pair of telephone wires 16. The broadband signal on lines 254 and 256 is significantly degraded, but is reconstructed beginning with the symmetrical video transformer video portions 250 and 252 of Figs. 13a and 13b.
The symmetrical video transformer circuit portions 250 and 252 include circuit components as listed in Table 2.
The values of the resistor and capacitor components are listed in Table 2, as are the part or model designations of the diodesl transistors and the operational amplifiers required .

WO 95120287 2 1 8 2 0 Q 2 PCrNS94100433 ~AB~B_2 r, ent VAllle~Designation 13IC1 -- 78N15C ~AI
13D1 = IN 400.
1.D2, 13D4 = IN 414 1.D = BZX83C-V3 l.Cl = 0 22 m- crofarads, 100 volts 1JC2, 13C3, 13C7 = 10 m_crofarads, 35 VO1tg 1.C4 = 220 microfarads, 3 volts l.C5 = 47 farads, 3 volts 1-C6 = 22 farad5, 3 volts 1,C8, 13C9, 13C10 = Variable 25 to 500 picofaraas 13T1 ~ BC33840SIE
13T2, 13T5, 13T6 = BC548B

13T ~ BF324SIE
13R1 = 22 ohms, 15 volts 13R2, 1.R20 = 15R ohms 13R3, 1,R6 = 24 + 2~ ohms 13R4, 1.R7 = 18 + 2~ ohms 13R5, 1.R8 = 20 + 2~ ohms 13R9, 1.R23 = 22 ohms 1~R10 = _20R ohms 13R11, 13R21, 13R29 = _ 5R ohms 1_R12 = ~7R ohms 13R13 = ~DR ohms 13R14, 13R15 ~ ~R ohms 13R16 = ,~0 ohms 1-R17 = _ NTC ohms 13R18 = 10 NTC ohms _,R19 = 1R ohms _.R22 - 47 ohms _.R24 = _ 3R ohms _.R25 ~ _OR ohms _.R26 = _ 3R ohms _.R27 = _ 7K ohms _R28 = . 9R ohms _,R30 = 75 ohms 1-R31 = 150 ohms WO 95120287 PCr/US94/00433 The symmetrical video transformer circuit portion 250 of Fig. 13a includes resistor-capacitor combinations which are selected for connection into the symmetrical video transformer circuit 30 according to the impedance of the twisted pair link 16. This imrpri~nce~ in turn, is governed by the length of the twisted pair of tPl Prh~ne wires forming tbe link 16, as well as by the gauge of the wires.
The symmetrical video transformer circuitry 30 includes contacts 13A, 13B, 13C, 13D, 13E, and 13F which are normally open, but which can be bridged by soldered connections as required. Other resistor-capacitor combinations may be connected in circuit by plug-in bridges and are in~icatP~ at 13R, 13S, 13T, 13~1, 13V, 13W and 13X.
ArpP~ Y A hereto sets forth the different resistor-capacitor combinations which are selectively and alternatively strapped into the symmetrical video transformer circuitry, as determined for specific lengths and gauges of the twisted pair link 16. ~he appropriate resistor-capacitor combinations for other length and gauges of twisted pair links 16 can be determined empirically.
The signal leaves the second or receiving end 17 of the twisted pair link 16 and appears on lines 254 and 256 in the symmetrical video transformer circuit portion 250 of Fig. 13a. An imrell~nce matching transformer 266 part number G5603 is matched to the i~re~l~nce of the twisted pair link 16 and amplifies all of the information received on lines 254 and 256, including the data signals, the telephone signals, the audio component of the video signal and the Wo gs/20287 2 1 8 2 0 0 2 PCTn~sg4/00433 degraded video ~~ ~~n~l~t of the video signal. The il~lre~iAnce matching transformer 266 amplifies all of this information with a uniform gain. The transistors 13T3, 13T4, 13T5 and 13TC of Fig. 13b further amplify the receiYed signal to build up the signal level for correction.
Corr ec~ i ng P mnl if i e r The correcting amplifier circuit 32 includes amplifying portions 258 and 260, which are respectively set forth schematically in Figs. 14a and 14b. The correcting amplifier circuit 32 c- " R~tes for the imre-l~nce of the twisted pair link 16. The correcting amplifier circuit portion 258 is coupled to receiYe the amplified output from the i _-~Ance matching transformer 266 of the symmetrical video transformer circuit 30. The correcting amplifier circuitry portions 258 and 260 provide an offsetting impedance to the broadband signal transmitted thereto from the symmetrical video transformer circuit portion 260. This offsetting or ~ ,-n~ating i _flAn~e is proportional and in opposition to the known i~lredAnce of the twisted pair link 16 to thereby negate the effects of the known ;mre~Ance on the broadband signal. Table 3 lists the correcting amplifier components showing amplifiers and transistors by model number and the values of resistors and capacitors.

wo 95/20287 PC r/uss4l00433 Com7.~0nent Value/Designation 14IC1 = 78M15CFAI
14T1 = BC328405IE
14T~ = BFJ11 14T., 14T5, 14T6 = BC~48BVAL
14TL = BF~24SIE
14T, = BC 58C
14T8 = BC 48C
14T9 = BC558BSIE
14D1 = IN4003 14D2 = IN4148 14D = BZX55A9VI
14C1 = .22 m_crofarads, 100 volts 14C2 = 1~ m_crofarads, 35 volts 14C4 ~ 3~0 P cofarads 14C5 = 1 0 P_cofarads 14C6 = 8~. P_cofarads 14C7 = 1~0 p_co.~ara~s 14C, C21 = 270 p_co~ara~s 14C~ = 56 P CO ara~s 14C_O = 220 p_co'ara~ 8 14C_ = L'70 P CO ~ ara~s 14C__ = 1~l O p_coi ara~s 14C_~ 0 P CO ara~s 14C 4 = ~ 7 p_co: ara~s 14C15 = ~ P_cofarads 14C16 = 6 P_cofarads 14C17, 14C22 = 100 p_cofarads 14C18, 14C19, 14C20 = Variable 15 to 230 ~icofarads _4C~3, 14C24, 14C25 = 18 p_cofarads _4C 6 = 33 p cofarads 4C-7, C34 = 10 m_crofarads, 35 volts _4C~8 = .15 m- crofarads 14C~9 = 1 m_crofarads 14C,O = 2200 P cofarad8, 63 volts 14C_1, 14C32 = 22 m CrOfaradg, 16 volts 14C33 = 120 p_cofarads, 63 volts 14C35, 14C36 = 47 microfarads, 6.3 volts 14R1 = 15 ohms 14R2 = 56R ohms 14R3 S 470 10~+ ohms 14R4, R29 S 180 Ohm8 14R5 = 15R Ohm8 14R6, 14R16, 14R39 = 1R ohms 14R7 = 68R ohms 14R8 = 1. 6R ohms 14R9 Y 47R ohms 14R10 = 3R ohms Wo 9S/20287 PCr/US94/00433 21 820a~

~AR~.~ 3 (Continued) Com~onent Value/Designation 14R11, 14R20 = 1. 8R ohms 14R12 = 56 ohms 14R13, 14R27 = 2. 2R ohms 14R14, 14R37 = 3. 9R ohms 14R15, 14R28 = 33 ohms 14R17, 14R34 = 10R ohms 14R18, 14R25 = 47 ohms 14R19, 14R30, 14R32 = 22R ohms 14R21 = 100 ohms 14R22 = 2. 7R ohms 14R23 = 6 . 8R ohms 14R24, 14R41 = 68 ohms 14R: 6 = 1.2R ohms 4RJ1 = 470 ohms 4R~3 = 220R ohms 4R~5 = 3 . 3R ohms _4R~6 = 4.7R ohms _4R38 = 47 ohms 14R~O = 1. 3R ohms 14R~2 = 680 ohms 14R~3 = 330 ohms 14DR1 = 15 microhenrys 14DR2 = 15 microhenrys 14DR3 = 10 microhenrys 14DR4 = 33 microhenrys The correcting amplifier circuitry portions 258 and 260 are comprised of an emitter-~ollower amplifier circuit and a plurality of combinations of resistors, capacitors and inductors. At least one of the combinations of resistors, capacitors and inductors is coupled in the emitter follower circuit, and other of the combinations are selectively i ~ol ~ted therefrom in accordance with the i - '~nce of the twisted pair link 16. These resistor-capacitor-inductor combinations are selectively coupled in circuit and isolated by means of normally open bridges 14A, 14B, 14C, 14D, 14E, 14~, 14G, 14H, 14I, 14J, 14R and 14L which can be selectively closed by soldering, and by normally open plug-in brid9eS 14R+, 14S~, 14T, 14~, 14V, 14W, 14X, 14X~, 14Y, wo 9~20287 PC r/uS94/00433 14Y+, 14Z and 14Z+. The closures of these bridges for several selected lengths and gauges of different twisted pair of links 16 are set forth in Appendix A.
The amplified broadband video signal leaves the symmetrical video transformer circuit portion 252 on a signal output line 268. The 6ignal output line 268 is connected as an input to the correcting amplifier circuit portion 258 in Fig. 14a. The bridging connections of Fig.
14a selectively connect resistors 14R10 through 14R18 and capacitors 14C5 through 14C15 into the amplifying circuitry of the correcting amplifier circuit portion 258 to partially cate for the i~rerlAnce of the twisted pair link 16.
The correcting amplifier circuit portion 260 performs the phase ad~ustment necessary to complete the correction for the impedance of the twisted pair link 16.
The signal output lines 270, 272 and 274 from the correcting amplifier circuit portion 258 of Fig. 14a are connected as inputs to the correcting amplifier circuit portion 260 of Fig. 14b. The bridging contacts 14E, 14F, 14G, 14e, 14I, 14J, 14K, 14L, 14T, 14~, 14W and 14V are used to strap in the resistor-capacitor-inductor combinations that ad~ust the phase of the received broadband signal in order to reconstruct that signal.
The circuit portion 258 of the correcting amplif ier circuit 32 serves as a trimming circuit and simulates a few turns of wire, 80 as to ~ ~ -ate for any minor mi c~--tch between the imredAnce matching transformer 266 and the impedance of the twisted pair link 16. The correcting Wo 95l20287 2 1 8 2 0 a 2 PCTIUSg4l00433 amplifier circuit portion 258 of Fig. 14a also functions as a received signal emitter follower amplification circuit.
The resistor-capacitor combinations in the correcting amplifier circuit portion 258 are selectively and alternatively strapped into the received signal emitter follower amplification circuit as determined by the length of the twisted pair link 16. The correcting amplifier circuit portion 260 of Fig. 14b forms a phase adjustment means for applying a phase adjustment to the video signal.
The circuit portion 260 employs resistor-capacitor-inductor combinations which are selectively and alternatively strapped into the phase adjustment amplifier circuit as determined by the length of the twisted pair of telephone wires 16.
Together the symmetrical video transformer circuit portions 250 and 252 and the correcting amplifier circuit portions 258 and 260 form a unity gain amplification means that is coupled to the second end 17 of the twisted pair link 16 to reproduce the video signal 55 with a ~~ ~ating -~nce impressed thereon that is proportional and opposite to the known impedance of the twisted pair link 16.
The ir~P~nce impressed upon the signal by the correcting amplifier circuit portions 258 and 260 is equal to and cancels out the effects of the line i~r~ nce in the twisted pair link 16.
The final signal output line 276 from the correcting amplifier circuit portion 260 carries a broadband signal which is restored to the configuration of Fig. 3. Tbe Wo 95/20287 PCTrUSs4/00433 output signal on line 276 in the correcting amplifier circuit portion 260 is a fully reconstructed broadband signal, includiny all of the signal components of Fig. 3.
The correcting amplifier circuitry reconstructs all of the signals, including the video signal 55. That signal is fully recQnstructed and complete with horizontal sync pulses and color information in the video signal 55.
~ - lation As the fully reconstructed composite broadband signal of Fig. 3 leaves the correcting amplifier circuitry on line 276 of Fig. 14b, it is pagged to d - lAt;n~
circuitry indicated generally at 26 in Fig. 1. The demodulating circuitry 26 forms a frequency division d: la~;ng means that is coupled between the ;mre~Ance ~- ~ating means of Figs. 13a, 13b, 14a and 14b and the receivers for each of the signal components, indicated at 20, 34', 36', 38', 40' and 42' in Fig. l. The demodulating circuitry 26 employs many of the same subcircuits of the modulating circuit 24.
The d - la~;ng circuit 26 is depicted in block diagram form in Fig. 4. The demodulating circuit 26 removes the carrier frequency from each of the telephone and data channels and directs the signal component to an appropriate receiver. That is, as illustrated in Fig. 1, the reconstructed video signal 43', having reconstructed audio and video components 44', 46', is directed to a television receiver 20. The reconstructed telephone signal is directed to a telephone handset 34 ', which is identical to the WO 9s/20287 2 1 8 2 0 0 2 PCT~us94/00433 telephone handset 34. Similarly, the data signal from the data modem transmitting module 36 i3 directed to a data modem receiving module 36'. The data signal from data modem transmitting module 38 is directed to a data modem receiving module 38 ' . The data signal from data modem transmitting module 40 is directed to a modem data receiving module 40 ' .
The data signal from the data modem transmitting module 42 is directed to a data modem receiving module 42 ' .
The system of Fig. 1 illustrates two 6tations 12 and 14 which are connected directly to each other by a twisted pair link comprised of a single pair of telephone wires 16.
It is to be understood, however, that the system is equally applicable to stations connected in a nationwide or worldwide telec n i cation network .
Fig. 15 illustrates such a system in which the station 12 is connected by an unloaded twisted p2ir of telephone wires 316 to a telephone central office 318. The central office 318 is connected into a nationwide common carrier telecommunication network inc]ucling buried and overhead coaxial cable, fiberoptics, laser, microwave, satellite and infra-red telec-- nications links, indicated generally at 324. The station 14 is likewise c~nn~cted to a central office 320 by an unloaded twisted pair of telephone wires 322. The central office 320 is also connected into the same common carrier telecommunications network 324.
Thus, the invention may be applied to stations which are connected to each other by a mere six th~ S~nA feet of a twi8ted pair of telephone wireS as illustrated in Fig. 1, or . .... . . _ .... . _ _ _ _ .

wo 9s/20287 Pcrluss4l00433 to stations located ~h~ RAntlq of miles apart and connected to each other by a twisted pair link including component lengths of pairs o~ twisted telephone wire 316 and 322 through central offices 318 and 320 and a common carrier 324 .
It is to be understood that the telec- ication system of the invention is not necessarily connected to either 2 local or nationwide telephone network. To the contrary, the stations 12 and 14, if located in physical proximity to each other, could be connPct~d together directly by a single length of an unloaded twisted pair of telephone wires. The operation of the invention is the same whether the stations 12 and 14 are connected directly together by a single length of an unloaded twisted pair of tPleph~ne wires 16, or by se~tionc of twisted pairs 16 that extend to local t~1~rhorle central offices, which are connected together through a nationwide telephone network.
Regardless of the distance over which the signals are transmitted beyond the twisted pair link, full reconstruction of the video signal 55 is possible.
The preferred ~ ts of the tele~~ ication system of the inYention provide simultaneous, switchable communication of full motion color video with interactive voice and integrated data capabilities. The system employs a multipleYer switch enhancer which ~A~ 'qAtes~
redistributes and manages the bi-directional transmission of full motion color images, as well as audio and data chAnnf~l c as desired.

Wo9s/20287 2 1 8 2 0 0 2 PCrluss4l00433 While the t~let nication system of the invention has been illustrated as transmitting and receiving a single video signal, as well as additional telephone and data signals, it is to be understood that the system is readily AAIrtAhle for the transmission and receipt of a plurality of video signals. That is, using quadrature amplitude modulation techniques the system can acc -~te up to four channels of full motion, color, video instead of the single video channel with a telephone and four data channels as described in the ~ t of Figs. 1-14b The telc. ;cation system of the invention provides analog ir~on enhancement and capability transmitted over a twisted pair of telephone wires. The 6ystem can be used for the twin wire transmission of bi-directional video, voice, data, ~acsimile or telexed inputs and outputs from office to office, floor to floor, within a building or compleY of buildings, and between buildings, studios and stations of distance up to six thousand feet over unloaded pairs of telephone wires.
As illustrated in Fig. 1, the system can be constructed for full duplex operation. In such a system each of the stations 12 and 14 includes full transmit and receive capabilities. The telec~ ication system of the invention may be either simplex, half duplex, or full duplex, and may be employed for special purposes, such as home video, paper viewing, video conferencing, security surveillance, medical and health care delivery, the monitoring of nuclear power plants, and innumerable other wo 95/20287 Pcr/uS94/00433 2 1 82~Q2 applications .
Undoubtedly, numerous variations and modifications of the invention will become readily apparent to those familiar with teleo. ica~ions systems. For eYample, the selectable contacts of Arp--n~;Y A need not be soldered or plug-in connPc~inn~ as depicted in the drawing figures, but can be est~hl i qhPd through an EPRON. That is, the length and gauge of the wires in the twisted pair link can be programmed into the EPROM so that the appropriate contacts will be es~hli sh~-d automatically. Accordingly, the scope of the invention should not be construed as limited to the specific ~ Ls of the tel~-- ni~tion system depicted and described, but rather is defined in the claims appended hereto.

W095~20287 2 1 8 2 0 3 2 PCrlUSs4l00433 APPENDI~ A
PLUG IN STRAPS AND SOLDER BRIDGES W~IC~ MUST BE
CLOSED FOR VARIOIJS WIRE LE~GTEIS, GAUGES AND TYPES
LENGT~ OF LINE SYM VIDEO CORRECT
LINE DRIVE~ 19 T~AN.~ 30 A~qP 32 20 AWG -- Poly--vinvl nh7 oride TnRulation tPVC) 1320 - 2475 ft B,A,W G
2970 -- 4125 ft B,A,W G,D,E,A
4620 -- 5775 ft A,III,VI T,R,B,L,V,X G,R+,D,E,A
26 AWG - PolY-ethvlene TnRTllatiOn (PE) 1320 - 2475 ft B,A,W G
2970 -- 4125 ft T,R,B,A,W G,R+,D,A
4620 -- 5775 ft A,III,E,G ~,S,B,L G,R+,D,A
. AwG - PE
Tn Rll l ated 1815 -- 3300 ft B,A,W G
3960 -- 5610 ft B,A,W G,D,C+,A
6270 -- 7755 ft A,B,III T,R,B,L,A,W G,R+,D,C+,A

Inculated 2145 - 4125 ft B,A,X G
4950 -- 6930 ft B,A,X G,D,C+,E,B,A
7755 -- g570 ft A,B,III,VI T,R,B,L,A,V,W,X G,R+,D,C+,E,B,A

Tn Rll 1 A ted 2475 -- 4785 ft ~,A,X G
5600 - 7920 ft ~,A,X G,D,C+,E,B,A
8745 - 110S5 ft A,B,III,VI B,L,A,V,W,X G,R+,D,C+,E,B,A
Notes: R+ stands alone and D stands 210ne - should not be r ead as ~R+D ) .
R+ was used as not to confuse "R" for resistor.
C+ was used as not to confuse "C" for capacitor.
26 AWG - Paper TnR~- 7 ~ted 990 -- 1980 ft B,A G
2310 - 3300 ft B,A G,D~B
3630 - 4455 ft A,III B,L,W G,D,B

WO 95/20287 PCrlUS94100433 LENGT~ OF LINE SY~l VIDEO CORRECT
LINE nRTVEF~ 19 Tl~Al~.C; 3 0 Ar~P 32 22 AWG - Paper TnRIl 1 ated 1485 -- 2805 ft B,W G
3465 -- 4785 ft B,W G,D,A
5280 -- 6600 ft A,B,III B,L,X G,D,A
20 AWG - P~r~er In ~ ted 1650 -- 2970 ft B,A,W G
3630 -- 4950 ft B,A,W G,D,C+,A
5610 -- 6930 ft A,III,VI B,L,A,X G,D,C+,A
22 AWG -- PolY--vi nVlrhl oride Tn~lll Ition tPVCj 825 -- 1485 ft B,A,W G
1815 -- 2475 ft T,R,B,A,W G,D,C+,A
2805 -- 3465 ft A,B,III,F,G T,R,B,L,A,X G,D,C+,A
III = RO~5ANS 3 VI 5 ROr~ANS 6

Claims (20)

IN THE CLAIMS

1. A telecommunication circuit for transmitting video signals comprising:
video signal initiation means for providing a broadband video signal of at least 4.5 megahertz band width, line driver means coupled to said video signal initiation means to amplify said broadband video signal and transmit it intact, a link formed of a twisted pair of unloaded telephone wires having opposite ends one of which is coupled to receive said amplified broadband video signal, symmetrical video transformer means coupled to the other of said ends of said twisted pair link to receive and amplify said broadband video signal, correcting amplifier means coupled to receive said broadband video signal from said symmetrical video transformer and to impress thereon an impedance proportional to the impedance in said twisted pair link and in vector opposition thereto to thereby correct said broadband video signal for impedance degradation in said twisted pair link, and a video receiver coupled to said correcting amplifier means for receiving said corrected broadband video signal.

2. A telecommunication circuit according to Claim 1 wherein said broadband video signal as provided by said video signal initiation means has a band width of at least 6.0 megahertz.

3. A telecommunication circuit according to Claim 1 wherein said twisted pair link is no greater than six thousand feet in length.

4. A telecommunication circuit according to Claim 1 wherein said correcting amplifier means is comprised of a receive signal emitter follower amplification circuit and resistor-capacitor combinations which are selectively and alternatively strapped into said receive signal emitter-follower amplification circuit as determined by the length of said twisted pair link.

5. A telecommunication system according to Claim 4 wherein said line driver means is comprised of a gain selection means including a transmit signal emitter follower amplification circuit and resistor-capacitor combinations which are selectively and alternatively strapped into said transmit signal emitter follower amplification circuit as determined by the length of said twisted pair link.

6. A telecommunication circuit according to Claim 1 wherein said correcting amplifier means is comprised of phase adjustment means for applying a phase adjustment to said video signal.

7. A telecommunication circuit according to Claim 6 wherein said phase adjustment means is comprised of a phase adjustment amplifier circuit and resistor-capacitor-inductor combinations which are selectively and alternatively strapped into said phase adjustment amplifier circuit as determined by the length of said twisted pair link.

8. A telecommunication circuit according to Claim 1 further comprising at least one voice band signal initiation means for providing a voice band signal of about 4 kilohertz band width and multiplexing means coupled to receive said broadband video signal from said video signal initiation means and said voice band signal from said voice band signal initiation means and to transmit said broadband video signal and said voice band signal simultaneously to said line driver means over said twisted pair link, and a voice band receiver coupled to said correcting amplifier means for receiving said voice band signal.

9. A telecommunication circuit according to Claim 8 comprising a plurality of voice band signal initiation means as aforesaid including at least one telephone signal initiation means and at least one data signal initiation means and a plurality of voice band receivers as aforesaid dedicated to receive each of said voice band signals.

10. A telecommunication circuit according to Claim 8 wherein said multiplexing means is comprised of frequency division modulating means coupled between said signal initiation means and said line driver means and frequency division demodulating means coupled between said correcting amplifier means and said receivers.

11. A telecommunication system comprising:
(a) a video signal source providing a broadband video signal having a frequency band width of at least 4.5 megahertz, (b) line driver means coupled to said video signal source to produce an amplified broadband video signal;
(c) a link comprised of an unloaded twisted pair of telephone wires having a known impedance and coupled to receive said amplified broadband video signal intact from said line driver means, (d) a symmetrical video transformer coupled to said twisted pair of telephone wires to receive and amplify said broadband video signal therefrom, (e) correcting amplifier means coupled to said symmetrical video transformer to impress thereon an offsetting impedance to said broadband video signal emanating from said twisted pair link which is proportional and in opposition to said known impedance of said twisted pair link to thereby negate the effects of said known impedance on said broadband video signal from said video source, and (f) a video receiver coupled to receive said broadband video signal from said correcting amplifier means to extract a video image therefrom.

12. A telecommunication circuit according to Claim 11 wherein said correcting amplifier means is comprised of an emitter follower amplifier circuit and a plurality of combinations of resistors, capacitors and inductors, and at least one of said combinations is selectively coupled in said emitter follower circuit and other of said combinations are selectively isolated therefrom in accordance with the impedance of said twisted pair link.

13. A telecommunication circuit according to Claim 11 wherein said symmetrical video transformer and said correcting amplifier means serve as a unity gain amplifier for signals passing over said twisted pair link.

14. A telecommunication circuit according to Claim 11 further comprising at least one additional signal source for providing at least one additional communication signal, and frequency modulating means coupled to receive said signals from said signal sources and to modulate said signals, and said line driver means is coupled to said frequency modulating means to receive said modulated frequencies therefrom and further comprising demodulating means coupled to said correcting amplifier means to receive modulated signals therefrom, and to demodulate said modulated signals to separately reproduce said broadband video signal and each additional communication signal, and separate communication receivers for each additional communication signal.

15. A telecommunication circuit according to Claim 14 further comprising a plurality of additional signal sources as aforesaid including at least one additional telephone signal and at least one additional data signal.

16. A telecommunication circuit according to Claim 14 further characterized in that said additional communication signal is about 4 kilohertz in bandwidth.

17. A telecommunication circuit according to Claim 11 further characterized in that said twisted pair link is no greater than six thousand feet in length.

18. In a telecommunication circuit including a twisted pair link comprised of an unloaded twisted pair of wires of a known length and having first and second ends, the improvement comprising:

video signal provision means for providing a broadband video signal having a band width of at least 4.5 megahertz, line driver means interposed between said video signal provision means and said first end of said twisted pair link to amplify said broadband video signal intact and to impress a known impedance thereon, whereby said twisted pair link exhibits said known impedance unity gain amplification means coupled to said second end of said twisted pair link to reproduce said broadband video signal intact with a compensating impedance proportional and opposite to said known impedance impressed thereon, and a video receiver coupled to receive said broadband video signal with said compensating impedance impressed thereon.

19. An improved telecommunication circuit according to Claim 18 wherein said unity gain amplification means is comprised of a symmetrical video transformer at said second end of said twisted pair link to amplify said broadband video signal, and correcting amplifier means for impressing said compensating impedance on said broadband video signal once it emanates from said symmetrical video transformer.

20. A telecommunication circuit for transmitting a broadband video signal of at least 4.5 megahertz band width over a link formed of a twisted pair of unloaded telephone wires having opposite ends, comprising:
symmetrical video transformer means coupled to one of said ends of said twisted pair link to receive and amplify said broadband video signal; and correcting amplifier means coupled to said symmetrical video transformer for impressing on said broadband video signal an impedance proportional to the impedance in said twisted pair link and in vector opposition thereto to thereby correct said broadband video signal for impedance degradation in said twisted pair link.