AU677032B2

AU677032B2 - TV/VF splitter

Info

Publication number: AU677032B2
Application number: AU57813/94A
Authority: AU
Inventors: Bruce Francis Orr
Original assignee: Alcatel Australia Ltd
Current assignee: Nokia Services Ltd
Priority date: 1993-04-07
Filing date: 1994-03-16
Publication date: 1997-04-10
Anticipated expiration: 2014-03-16
Also published as: AU5781394A; NZ260095A

Description

P/00/01 1"28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT C

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Invention Title: "TV/VF SPLITTER" The following statement is a full description of this invention, including the best method of performing it known to us:-

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4* C C C CCC 2 This invention relates to a device for use in injecting high frequency signals onto a tvvo-wire line intended to carry low frequency signals, and to a device separating the high frequency signals from the low frequency signals.

A paiticular application of the invention is in the transmission of television signals over telephone lines.

Background of the Invention It is proposed to implement a form of cable television by transmitting television signals over subscribers' telephones lines. With modern compression and transmission techniques it is possible to transmit digital TV signals over a bandwidth of the order of 1MHz. This is, however, far in excess of the nominal frequency of a telephone line which is of the order of 10 kHz. As a result, the *0 signals are significantly attenuated, the attenuation increasing with frequency.

One technique for transmitting high rates of information is Discrete Multi-Tone (DMT). DMT involves the splitting of a bandwidth into several channels and transmitting tones in the channels to represent information.

This invention serves the purpose of providing means to apply high frequency oo° signals to a two-wire line, such as a phone line, in such a manner that normal phone signals can also be applied to the line. The invention also serves the purpose of providing means for extracting the high frequency signals from the o~e• line.

Summary of the Invention This specification discloses a signal combining device to combine a first signal having a first frequency band with a second signal having a second frequency 3 band higher than the first frequency hand into a two-wire line, the device including a first transformer having first second and third windings, the third winding being magnetically coupled to the first winding (and the second winding); the first and second windings being magnetically coupled so that a signal induced in the first winding by the third winding induces a signal in the second winding; the first and second windings being coupled in series via a first capacitor so that the signal induced in the second winding is added to the signal induced in the first winding; the distal ends of each of the first and second windings each being

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connected to a respective one of the wires of the two-wire line; wherein the first signal is applied across the first capacitor; oo the second signal is applied to the third winding; the first capacitor being substantially open circuit to the first signal and short circuit to the second signal.

eo The specification also discloses a device for separating the signals at the *0 S receiving end.

Brief Description of the Drawings 20 Figure 1 shows an arrangement for transmitting frequency separated signals over a telephone line to a subscriber, including devices at both ends embodying the invention.

Figure 2 shows an arrangement of devices for use in a telephone

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exchange to transmit TV signals via subscribers' lines.

Figure 3A and 3B show an embodiment of the invention for extracting TV and phone signals at the subscriber' premises.

Figure 4 shows an extraction device where the subscriber has extension lines.

Figure 5 shows an alternative embodiment for Figure 4.

Description of the Invention Figure 1 shows an arrangement for transmitting voice signals and TV signals from a central location to a subscriber over the subscriber's phone line, and for separating the signals at the subscriber's premises. The arrangement can also be used to permit the subscriber to transmit signals to the central *4 location in a frequency band above the voice signals. This could be used, eg., to change the channel selected by the subscriber where the central location can eaoo access a plurality of such channels in response to the request signal from the subscriber. The subscriber's request could be detected by the third winding W3 of the transformer at the central location and separated from the TV signals by •coo known means such as filters or hybrid circuits.

S. The arrangement of Figure 1 includes at a central location such as a

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telephone exchange a device 1 for combining voice and TV signals. The device includes a first transformer T1 consisting of windings W1, W7, and W3.

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Windings W1 and W2 are connected in series electrically in a high frequency path by capacitor C1. The voice signals are applied across C1 which is effectively open circuit to the voice frequencies. Optionally the voice signals are applied via a pair of windings W4, W5 which serve to block noise signals above the voice 'and which may interfere with the TV signals. These noise signals may be generated, eg., by the ring signal generator.

The windings W1, W2 and W3 are poled as indicated so that signals induced in W2 add to signals induced in W1 across the subscriber line (L1, L2).

The TV signals are applied to winding W3 and may be in the forrr of a plurality of tones of different frequencies spread over a bandwidth of the order of 1 MHz. A low frequency blocking capacitor C3 may be added in series with W3 to prevent voice signals being fed to the TV signal source.

At the subscriber's end of the line there is a splitter 2 including a transformer consisting of windings W6, W7 and W8. W6 and W7 are again connected in a high frequency path by a capacitor 02. Voice signals are 0 extracted across 02, and the TV signals are extracted via W8. Optionally low °o°O° frequency capacitor C4 prevents voice signals appearing in the TV signal output.

Figure 2 is a drawing illustrating a physical embodiment of the combiner .f Figure 1 *.000.

The combiner includes a connector block 21, a plurality of signal transformers T 1 to Tin, a plurality of capacitors C11 to Ci n, and a plurality of .000 blocking transformers T21 to T2n, all mounted on a PCB 22. This arrangement

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20 enables n lines to carry both signals.

0*0*0* This arrangement is designed to be mounted on the MDF (main (distribution frame) of an exchange so that the combiners can be added with a minimum of change to an exchange. The n subscriber lines enter the PCB 22 from the exchange via a section of the connector block 21 and each line is connected to one of the signal transformers (T1 1 to Ti one of the capacitors (C11 to CGin) and one of the blocking transformers (T21 to T2n) as shown in Figure 1. The TV signals are applied to the W3 windings of transformers T11 to Ti n via a second portion of the connector block, and the subscriber lines are connected to a third portion of the connector ulock. The connector block may be, eg. a Krone insulation displacement type.

Figure 3A shows a splitter to be for use at the subscriber's premises. The splitter includes connector pins 31 and 32, and locking lug 33 compatible with the standard Australian telephone phone line socket so that the splitter can be plugged directly into the phone socket. The other side of the splitter includes a socket (34, 35, 36) compatible with the conventional phone line plug so that the phone can be plugged into the splitter. The splitter also includes a socket 37 from which the TV signal is extracted. The socket 37 is connected to the winding W8 (and optional capacitor C4) of Figure 1.

This arrangement provides a simple plug in modification at the ••ee subscriber's premises.

The TV signals may then be fed from socket 37 to an amplifier which has 0 a gain characteristic to compensate for the frequency dependent line losses.

00 20 Figure 3B shows a profile of the embodiment of Figure 3A.

°o..oi The embodiments of Figure 3 are suitable where the subscriber has a single phone. The embodiment of Figure 4A is suitable for the case in which the subscriber has extension phones.

7 In this case an additional module 4 is interposed between the phone socket and the exchange line. The module 4 carries the splitter and has three pairs of terminals X1, X2; X3, X4; and X5, X6, to which are applied respectively the exchange line, the subscriber's side phone line, and the output line for the TV signals. The subscriber's side phone line is then connected to the existing plug and socket arrangement.

Figure 5 shows an alternative arrangement for use where the subscriber has extension lines. In this case the module 5 is similar to the arrangement of Figure 4 but includes a first phone socket into which the first phone can be plugged directly. A phone line to the extension socket is taken off from terminals X11, X12.

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Claims

1. A signal combining device to combine a first signal having a first frequency band with a second signal having a second frequency band higher than the first frequency band into a two-wire line, the device including a first transformer having first second and third windings, the third winding being magnetically coupled to the first winding and the second winding; the first and second windings being magnetically coupled so that a signal induced in the first winding by the third winding induces a signal in the second winding; the first and second windings being coupled in series via a first capacitor so that the signal induced in the second winding is added to the signal induced in the first winding; the distal ends of each of the first and second windings each being connected to a respective one of the wires of the two-wire line; wherein the first signal is applied across the first capacitor; the second signal is applied to the third winding; the first capacitor being substantially open circuit to the first signal and short circuit to the second signal.

2. A device as claimed in claim 1 wherein the first signal is applied via high frequency choke means.

3. A device as claimed in claim 2 wherein the high frequency choke means comprises first and second coils, each connected to a corresponding plate of the first capacitor.

4. A device as claimed in any one of claims 1 to 3 wherein the third winding is connected to means to extract a third signal received from the line, the third signal having a frequency band different from the first and second signals.

I. A device as claimed in claim 4 wherein the extraction means comprises a hybrid circuit.

6. A device as claimed in claim 4 wherein the extraction means comprises a 30 filter which excludes the first signals and the second signals. IN rC

7. A device as claimed in any one of claims 1 to 6, including a low frequency blocking capacitor in series with the third winding.

8. A printed circuit board arranged to be mounted on an MDF of an exchange and carrying a plurality of devices as claimed in any one of claims 1 to 7 and connector means to which the exchange line, a subscriber's line, and TV signal line can be connected.

9. A splitter device for separating a first signal and a second signal on a two-wire line the first signal having a frequency band lower than the band of the second signal, the device including a transformer having inductively coupled first, second and third windings, the first and second windings being connected in series in a high frequency path via a second capacitor which passes the second signal, the second capacitor acting as a block to the first signal, the first signal being taken off across the second capacitor, the second signal being taken off from the third winding.

10. A splitting device as claimed in claim 9 including a low frequency blocking capacitor in series with the third winding.

11. A splitting device as claimed in claim 9 or claim 10, including means to inject a third signal onto the two-wire line via the third winding, the third signal having a frequency band different from the first and second signals.

12. A splitting device as claimed in any one of claims 9 to 11, wherein the line is a telephone line and the device includes an input plug compatible with an exchange line socket and a first output socket compatible with a phone's line plug, and a third socket connected to the third winding via which the second signals can be extracted.

13. A splitting device as claimed in any one of claims 9 to 11 including a plurality of terminal pairs to which an exchange line, the second signal and a phone line respectively can be connected.

14. A splitting device as claimed in claim 13 including a conventional phone socket.

15. A splitter device as herein described with reference to Figures 1, 3, 4 and R LU of the accompanying drawings.

16. A combiner device as herein described with reference to Figures 1 and 2 of the accompanying drawings. DATED THIS THIRTIETH DAY OF JANUARY 1997 ALCATEL AUSTRALIA LIMITED ee oo oo o o*o *157H *j ABSTRACT The arrangement enables TV and voice signals to be transmitted from an exchange to a subscriber by providing, at the exchange, a combiner comprising a transformer W1, W2, W3 having a balanced loading effect on the line by having first and second windings W1, W2 in corresponding wires of the phone line. The TV signals are injected into the line via winding W3. Capacitor C1 shunts high frequency noise from the exchange so that it does not interfere. Optionally balanced choke windings W4, W5 also prevent high frequency signals from passing oetween the exchange and the transformer. At the subscriber's premises a second transformer W6, W7, W8 splits off the high frequency signals, and passes the VF signals to the phone, C2 preventing the high frequency signals reaching the phone. FIGURE 1. 0• coo I