WO2006012681A1

WO2006012681A1 - Method and device for power line head-end data transmission

Info

Publication number: WO2006012681A1
Application number: PCT/AU2005/001129
Authority: WO
Inventors: Donald Malcolm Ross Yelland
Original assignee: Donald Malcolm Ross Yelland
Priority date: 2004-08-02
Filing date: 2005-07-29
Publication date: 2006-02-09

Abstract

A coupler (400) for directional coupling to a power line, for use as a head-end coupler, repeater and/or tail end coupler in a power line communications environment. The coupler (300) has a primary winding (302) in series between a first port (304) and a second port (306), for carrying electrical power and for coupling communication signals. One or more communications windings (330) are inductively coupled to the primary winding (302) in a communication frequency band and substantially isolated from the primary winding (302) in a power frequency band. A capacitor filter (310) at the first port (304) removes communication signals at the first port (304) while permitting power flow through the first port (304).

Description

"Method and device for power line head-end data transmission"

Cross-Reference to Related Applications

The present application claims priority from Provisional Patent Application No 2004904333, 2004905003 filed on 2 August 2004, 1 September 2004, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to directional coupling of communication signals such as data, video or voice signals onto and from a power line, such that the communication signals are coupled to and from only one side of a coupling point on the power line.

Background to the Invention

Power line communication involves transmitting communication signals over electric power lines or cables, concurrently with power transmissions on the same power line or cable. Power line communication allows existing electrical power outlets to serve the additional role of signal and data ports. Numerous power line communication standards are available. Electricity transmission and/or distribution networks, being the largest deployed networks in the world, offer a pre-existing infrastructure for signal transmission networks using power line communication.

Previous attempts to establish primary head-ends have been limited by signal leakage leading to bandwidth saturation and privacy issues, unless signal conditioning networks have been installed, which have traditionally been cumbersome and/or expensive. Further, head-end components of power line communication systems have been very susceptible to unwanted noise and spikes, having deleterious effects and requiring explicit additional line protection to minimise damage.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Summary of the Invention

According to a first aspect the present invention provides a directional coupler for a power line, comprising: a primary winding in series between a first port and a second port, for carrying electrical power and for coupling communication signals; at least one communication signal carrying winding inductively coupled to the primary winding in a communication frequency band and substantially isolated from the primary winding in a power frequency band; and a filter at the first port for minimising communication signal flow through the first port, while permitting power flow through the first port.

According to a second aspect the present invention provides a method of directionally coupling communication signals to a power line, comprising: providing a primary winding between a first port and a second port, for carrying electrical power and for coupling communication signals; inductively coupling at least one communication signal carrying winding to the primary winding in a communication frequency band, and substantially isolating the communication signal carrying winding from the primary winding in a power frequency band; and filtering the first port to minimise communication signal flow through the first port and to allow power flow through the first port.

In preferred embodiments of the invention, the primary winding may further provide a high impedance to communication signals between the first port and the second port.

The filter may be connected between the first port and a neutral port, and may comprise a pass band encompassing the communication frequency band and a stop band encompassing the power frequency band. Such a filter causes communication signals at the first port and neutral to be shorted such that communication signals at the first port and neutral are minimised.

Providing a filter at the first port to prevent communication signal flow through the first port is of importance where the first port is the supply or line side of the directional coupler, as such a filter ensures that communication signal flow through the second port is not transmitted over the power grid and thus communication signals at the second port are not made accessible to others on the grid. Accordingly, embodiments of the present invention may have particular application as a head-end component of a power line communication system operating over a local power network and requiring privacy from the external power supply. Further, by providing a device which isolates the communication signal carrying winding from electrical power flowing in the primary winding, embodiments of the present invention thus enable safe access to communication signal lines without risk of electrical power leakage or shock, enabling maintenance and installation of associated electronics without requiring particular power electrical skills and qualifications. Such embodiments thus provide great flexibility in the creation and packaging of communication signal circuitry and the like in such head end equipment.

Preferred embodiments of the invention further provide protection circuitry against surges and spikes. The filter preferably is further operable to prevent incoming signals or noise in the communication frequency band from passing through the first port, thus shielding the second port from such unwanted signals or noise.

According to a third aspect the present invention provides a power line communication system comprising: at least one communication device coupled to a local power network; and a directional coupler in accordance with an embodiment of the first aspect of the invention, configured to secure communication signal transmission over the local power network.

By providing a directional coupler which prevents communication signal flow from the first port, embodiments of the first to third aspects of the invention provide for a secure local area communications network provided over local power supply cables, while minimising transmission of any such communication signals externally from the local network, and while allowing normal power flow between the local power supply network and a power distribution or transmission network such as the power grid. For example the local power supply network may be the power cables within a single apartment, dwelling, building or facility.

In such embodiments, the directional coupler may be positioned at or proximal to a power supply point for that local power network, thus isolating communication signal traffic on power cables within the network from the general power grid. Such embodiments ensure such communication signals are delivered and recovered only in the intended downstream direction from the coupling feed to the intended electricity distribution and/or transmission network, which within an apartment, dwelling or building could be the "load" side and away from the supply or "line" side.

Communication signals may be coupled to and from the power supply network at a plurality of points on the local power supply network. Such coupling may be directional or non-directional. Embodiments of the first to third aspects of the invention may be applied in a local power network acting as a load, such that power flows from the supply or line side of the directional coupler to the local power network. Additionally or alternatively, embodiments of the first to third aspects of the invention may be applied in a local power network acting as a supply, such that power flows from the local power network to the supply or line side of the directional coupler.

According to a fourth aspect the present invention provides a power line communication signal repeater comprising: a first primary winding between a first port and a central connection, for carrying electrical power and communication signals; at least one first communication signal carrying winding inductively coupled to the first primary winding in a communication frequency band and substantially isolated from the primary winding in a power frequency band; a second primary winding between the central connection and a second port, for carrying electrical power and communication signals; at least one second communication signal carrying winding inductively coupled to the second primary winding in a communication frequency band and substantially isolated from the primary winding in a power frequency band; a filter at the central connection for minimising communication signal flow through the central connection while permitting power flow through the central connection; means to amplify communication signals received at the at least one first communication signal carrying winding for insertion by the at least one second communication signal carrying winding, and to amplify data received at the at least one second communication signal carrying winding for insertion by the at least one first communication signal carrying winding.

Embodiments of the fourth aspect of the present invention enable data signals carried in the first primary winding and the second primary winding to be at the same frequency. The filter may be connected between the central connection and neutral, and comprise a pass band encompassing the communication frequency band, and a stop band encompassing the power frequency band.

A repeater in accordance with the fourth aspect of the invention provides a simple and simply installed means by which the physical length of such a power line. communication transmission network may be extended. A repeater in accordance with the fourth aspect of the invention may be utilised to enable data routing, data signal conditioning, or data signal condition monitoring.

According to a fifth aspect, the present invention provides a coupling device for coupling a data node to a power line communications network, the coupling device comprising: a primary winding in series between a first port and a second port, for carrying electrical power and for coupling communication signals; at least one communication signal carrying winding inductively coupled to the primary winding in a communication frequency band and substantially isolated from the primary winding in a power frequency band; and a filter at the first port for minimising flow of signal components outside the power frequency band through the first port, while permitting power flow through the first port.

According to a sixth aspect, the present invention provides a method of coupling a data node to a power line communications network, the method comprising: providing a primary winding in series between a first port and a second port, for carrying electrical power and for coupling communication signals; inductively coupling at least one communication signal carrying winding to the primary winding in a communication frequency band and substantially isolating the communication signal carrying winding from the primary winding in a power frequency band; and filtering the first port to minimise flow of signal components outside the power frequency band through the first port, and to allow power flow through the first port.

The fifth and sixth aspects of the invention provide for signals beyond the first port to be filtered outside the power frequency range and thus provide for smoothed power signals beyond the first port. Some embodiments may thus provide for the data node power supply to be drawn from beyond the first port. The data node is thus provided with a filtered or smoothed power supply from which has been filtered some or all non-power frequency components. The fifth and sixth aspects of the invention recognise that local power networks are. often subject to significant noise outside the power frequency band, with a major source of such noise often being switch mode power supply units (PSUs), such as the PSUs of personal computers (PCs).

Additionally or alternatively, embodiments of the fifth and sixth aspects of the invention may be configured to prevent signals outside the power frequency band from propagating from the first port in order to prevent communication signals from propagating from the first port and thus reducing the risk of nodes connected beyond the first port eavesdropping on communications signals of the data node.

In embodiments of the fifth and sixth aspects of the present invention, filtering the first port to minimise flow of signal components outside the power frequency band may comprise filtering out signals in a noise frequency band, for example where the noise frequency band comprises frequencies typically produced by switch mode PSUs. Additionally or alternatively, filtering the first port to minimise flow of signal components outside the power frequency band may comprise filtering out signals in a communication signal frequency band. For example, the filter may comprise a bandpass filter centred upon the power frequency and having sufficiently steep rolloff to adequately remove noise and/or communication signals. Alternatively the filter may comprise a lowpass filter having a cutoff frequency above the power frequency and having sufficiently steep rolloff to adequately remove noise and/or communication signals. In accordance with the first to sixth aspects of the invention, the communication signals may comprise data, voice, video or other communication signals. The communication signals may be modulated in any manner suitable for transmission on an electricity distribution or transmission network. The communication frequency band may be in the range of 2-37MHz.

Brief Description of the Drawings

Embodiments of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a circuit diagram of a previous device for coupling communication signals onto and from a power line;

Figure 2 is a circuit diagram of a head end directional coupler in accordance with a first embodiment of the invention;

Figure 3 is a circuit diagram of a head end directional coupler in accordance with a second embodiment of the invention; Figure 4 is a circuit diagram of a power line communication signal repeater in accordance with a third embodiment of the invention; and

Figure 5 is a circuit diagram of a tail end coupling device in accordance with a fourth embodiment of the present invention. Detailed Description of the Preferred Embodiments

Figure 1 illustrates a known domestic electricity distribution network coupler 100 for coupling data to cables carrying power from a supply grid 120, and positioned on a domestic side of a power meter 122 and mains isolator 123. Coupler 100 comprises a primary winding 102 connected between a power line tap point 104 and a neutral or earth port 106 at a neutral or earth coupling 107. The primary winding 102 is inductively coupled to a data receive winding 108 and a data transmit winding 110 via transformer 112. A power line modem connected to windings 108, 110 may be used to extract and inject data signals on the power cables of local power network 130. Protection for the mains is provided by fuse 114, and data signals are isolated from the mains via capacitor 116 having discharge resistor 118.

While coupler 100 is suitable for multiple units in an intra-dwelling scenario, when used as a head-end injector as shown in Figure 1, the coupler 100 does not provide sufficient head end functionality. This system requires a power rated cable 124 and mains rated heavy duty fuse 114. A low pass filter or ferrite 126 is also required, to condition the distribution network which is prone to surges, spikes, noise and unwanted signals coming from the grid 120 via meter 122. Further, the coupler 100 injects data signals upstream into the meter 122 and into the mains backbone 120, increasing the probability of another system eavesdropping, and should many such systems be used for head end application, such upstream data injection may lead to a gradual accumulation of noise with associated available cable bandwidth saturation.

Figure 2 is a circuit diagram of a head end directional coupler 200 suitable for head end use in accordance with a first embodiment of the invention. Coupler 200 comprises a primary winding 202 connected in series with a first port 204 and a second port 206, and in parallel with surge protector 208. Protection circuitry 208 is used to limit any high frequency spikes possibly appearing across the primary side of the transformer winding or coupled transmission line 202. Power from grid 220 passes meter 222 and circuit mains isolator 224 to flow through primary winding 202 to a local power network 226. Mains isolator 224 may in alternate embodiments be incorporated within directional coupler 200.

A filter comprising capacitor 210 and having an accompanying electrical safety discharge resistor 212 connects port 204 to a neutral or earth port 214 at a neutral or earth coupling 216. This may be provided via a direct connector or a common neutral bar inserted into a slot where multiple head-end couplers are used to provide service to multiple portions of electricity distribution and/or transmission networks. Primary winding 202 is rated to carry the entire current plus the legislated safety margins and inductively couples communication signals to windings 230, 232, wound onto a common high frequency capable gapped ferrite core 234, which is of a material optimised for coupling of signals in the communication frequency band, which for example may be between 3 MHz to 37 MHz, and having negligible inductance at mains frequencies. In alternate embodiments the primary winding 202 may be a coupled parallel transmission line. Winding 230 is used to inject communication signals while winding 232 receives communication signals. Windings 230 and 232 and/or attached communication signal processing circuits are constructed to minimise communication signal transfer between winding 230 and winding 232.

Figure 3 is a circuit diagram of a head end directional coupler 300 in accordance with a second embodiment of the invention. Coupler 300 comprises a primary winding 302 connected in series with a first port 304 and a second port 306, and in parallel with surge protector 308. Protection circuitry 308 is used to limit any high frequency spikes possibly appearing across the primary side of the transformer winding or coupled transmission line 302. Power from grid 320 passes meter 322 and circuit mains isolator 324 to flow through primary winding 302 to a local power network 326. Mains isolator 324 may in alternate embodiments be incorporated within directional coupler 300.

A filter comprising capacitor 310 and having an accompanying electrical safety discharge resistor 312 connects port 304 to a neutral or earth port 314 at a neutral or earth coupling 316. This may be provided via a direct connector or a common bus-bar inserted into a slot where multiple head-end couplers are used to provide service to multiple portions of electricity distribution and/or transmission networks.

Primary winding 302 is rated to carry the entire current plus the legislated safety margins and inductively couples communication signals to winding 330, wound onto a common high frequency, capable gapped ferrite core 334, which is of a material optimised for coupling of signals in the communications frequency band which for example may be between 3 MHz to 37 MHz, and having negligible inductance at mains frequencies. In alternate embodiments the primary winding 302 may be a coupled parallel transmission line. Winding 330 is used to both inject and receive communication signals. Use of a single communication signal carrying winding 330 in coupler 300 enables communication signal modulation circuitry to be provided separately to coupler 300. Such an embodiment may be more convenient should the modulator/demodulator be physically separated by a significant distance, or should it be desirable to utilise a commercially available power line modem with an external power supply. Figure 4 is a circuit diagram of a power line communication signal repeater coupler 400 in accordance with a third embodiment of the invention. Repeater coupler 400 comprises a first primary winding 402 connected in series with a first port 404 and a central connection 406, and in parallel with surge protector 408. Protection circuitry 408 is used to limit any high frequency spikes possibly appearing across the primary side of the first transformer winding 402. Power passes through first primary winding 402 to central connection 406 and thence through second primary winding 452, which is in parallel with protection circuitry 458, to second port 454. A filter comprising capacitor 410 provides a low impedance path to signals above the bottom end of the communication frequency band from first primary winding 402 to a neutral or earth port 414.

First primary winding 402 and second primary winding 452 are rated to carry the entire current plus the legislated safety margins. First primary 402 inductively couples communication signals with transmit winding 430 and receive winding 432, wound onto a common high frequency capable gapped ferrite core 434, which is of a material optimised to couple frequencies above the bottom of the communication frequency band, and having negligible inductance at mains frequencies. In alternate embodiments the primary winding 402 may be a coupled parallel transmission line. Winding 430 is configured to minimise coupling with winding 432. Similarly, second primary winding inductively couples communication signals with transmit winding 480 and receive winding 482, wound onto a common high frequency capable gapped ferrite core 484 which is of a material optimised for the communication frequency band, and having negligible inductance at mains frequencies. Winding 480 is wound to minimise coupling with winding 482. Communication signals received at primary winding 452 are coupled to receive winding 482, from where such signals may be amplified and/or otherwise processed, then passed to transmit winding 430 for coupling to primary winding 402 and transmission from port 404. Similarly, communication signals received at primary winding 402 are coupled to receive winding 432, from where such signals may be amplified and/or otherwise processed, then passed to transmit winding 480 for coupling to primary winding 452 and transmission from port 454. Communication signals are prevented from flowing through connection point 406 by capacitors 410 and 460, having accompanying discharge resistors 412 of about 1 MOhms for domestic mains type voltages, such a resistor may be mandated by safety legislation. Capacitors 410 and 460 present a low impedance or short circuit at communication frequencies and thus bridge modulated communication signals at the central connection 406 with the neutral or earth port 414. Capacitors 410 and 460 are selected to have a cut off frequency just below the bottom end of the communication frequency band used by the power line modulation scheme adopted. For example, capacitors 410 and 460 may have a value of around 0.022uF. Capacitors 410 and 460 should comply with the necessary power safety standards applicable for the relevant standards. Capacitors 410 and 460 present a high impedance or open circuit to mains frequency signals typically at 50/60Hz but will pass the modulated communication signal to neutral or earth and thus prevent any communication signal flow through connection point 406. Accordingly, only amplified and or processed signals pass through repeater 400. A low pass choke may be provided at connection point 406, which may be a ferrite suppressor to eliminate feedback loops.

Figure 5 is a circuit diagram of a tail end coupling device 500 in accordance with a fourth embodiment of the present invention. Coupler 500 comprises a primary winding 502 connected in series with a first port 504 and a second port 306, and in parallel with surge protector 508. Protection circuitry 508 is used to limit any high frequency spikes possibly appearing across the primary side of the transformer winding or coupled transmission line 502. Power from a power source such as the power grid 520 passes through an upstream local network 540 to flow through primary winding 502 to power a data node 550. Other components may be connected downstream from the coupling device 500.

A filter comprising capacitor 510 and having an accompanying electrical safety discharge resistor 512 connects port 504 to a neutral or earth port 514 at a neutral or earth coupling 516. This may be provided via a direct connector or a common bus-bar inserted into a slot where multiple couplers are used to provide service to multiple portions of electricity distribution and/or transmission networks.

Primary winding 502 is rated to carry the entire current plus the legislated safety margins and inductively couples communication signals to winding 530, wound onto a common high frequency capable gapped ferrite core 534, which is of a material optimised for coupling of signals in the communications frequency band which for example may be between 3 MHz to 37 MHz, and having negligible inductance at mains frequencies. In alternate embodiments the primary winding 502 may be a coupled parallel transmission line. Winding 530 is used by data node 550 to both inject and receive communication signals.

The configuration of Figure 5 allows data node 550 to send and receive communication signals with upstream network 540, while providing a "tail-end" to such communication signals, in that communication signals present at port 506 are not passed downstream from port 504. The filtering provided by capacitor 510 not only prevents downstream transmission of such communication signals from port 504, but further provides for noise shielding of the power supply on a downstream side of port 504, such that the power connections 552, 554 of data node 550 are shielded from noise sources in upstream network 540 such as switch mode power supply units of personal computers. While in the present embodiment data node 550 is the only device shown with power connections 552, 554 downstream from coupling device 500, further devices may be connected downstream from coupling device 500. Such devices may utilise one or more directional couplers and/or tail-end couplers in accordance with the present invention to establish a second communications network separate to and shielded from the network 540. The tail end coupling device 500 may additionally or alternatively be utilised to shield the network 540 from noise sources beyond port 504, for example where further devices having power connections downstream from port 504 comprise switch mode power supply units. Capacitors 210, 310 and 510 in Figures 2, 3 and 5 have respective discharge resistors 212, 312 and 512 each about 1 MOhms for domestic mains type voltages, such resistors may be mandated by safety legislation. Capacitors 210, 310 and 510 present a low impedance or short circuit at communication frequencies and thus bridge the modulated communication signal at port 204, 304, 504 with the neutral, effectively shorting communication signals at that port to neutral. Capacitors 210, 310 and 510 are selected to have a low impedance to signals above the low frequency end of the communication frequency band used by the power line modulation scheme adopted. For example, capacitors 210, 310 and 510 may have a value of around 0.022uF. Capacitors 210, 310 and 510 should comply with the necessary power safety standards applicable for the relevant regulatory authorities. Capacitors 210, 310 and 510 present an open circuit to mains frequency signals typically at 50/60Hz but will pass the modulated communication signals, leading to communication signals passing only through port 206, 306, 506 and not through port 204, 304, 504. Capacitors 210, 310 and 510 additionally provide a low impedance path for signals above the low frequency end of the communications frequency band to neutral or earth, and thus capacitors 210 and 310 minimise mains-side signals passing into local power network 226, 326, and capacitor 510 minimises downstream side signals passing into network 540.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

I . A directional coupler for a power line, comprising: a primary winding in series between a first port and a second port, for carrying electrical power and for coupling communication signals; at least one communication signal carrying winding inductively coupled to the primary winding in a communication frequency band and substantially isolated from the primary winding in a power frequency band; and a filter at the first port for minimising communication signal flow through the first port, while permitting power flow through the first port. 2. The directional coupler of claim 1, wherein the filter is connected between the first port and a neutral port.

3. The directional coupler of claim 2, wherein the filter comprises a pass band encompassing the communication frequency band and a stop band encompassing the power frequency band. 4. The directional coupler of any one of claims 1 to 3, wherein the directional coupler is a head-end component of a power line communication system operating over a local power network and requiring privacy from the external power supply.

5. The directional coupler of claim 1, wherein the primary winding provides a high impedance to communication signals between the first port and the second port. 6. The directional coupler of any one of claims 1 to 5, further comprising protection circuitry against power surges and spikes.

7. The directional coupler of claim 4, wherein the local power network comprises power cables within one of: an apartment, a dwelling, a building and a facility.

8. The directional coupler of claim 4 or claim 7, wherein the directional coupler is positioned at or proximal to a power supply point for the local power network to isolate communication signal traffic within the network from the general power grid.

9. The directional coupler of any one of claims 4, 7 and 8, wherein communication signals are coupled to and from the local power network at a plurality of points on the local power network. 10. The directional coupler of any one of claims 4 and 7 to 9, wherein the local power network is a load.

II. The directional coupler of any one of claims 4 and 7 to 9, wherein the local power network is a supply.

12. A method of directionally coupling communication signals to a power line, comprising: providing a primary winding between a first port and a second port, for carrying electrical power and for coupling communication signals; inductively coupling at least one communication signal carrying winding to the primary winding in a communication frequency band, and substantially isolating the communication signal carrying winding from the primary winding in a power frequency band; and filtering the first port to minimise communication signal flow through the first port and to allow power flow through the first port.

13. The method of claim 12, wherein the filtering comprises connecting a filter between the first port and a neutral port.

14. The method of claim 13, wherein the filter comprises a pass band encompassing the communication frequency band and a stop band encompassing the power frequency band.

15. The method of any one of claims 12 to 14, for providing a head end coupler of a power line communication system operating over a local power network and requiring privacy from the external power supply.

16. The method of claim 12, wherein the primary winding provides a high impedance to communication signals between the first port and the second port.

17. The method of any one of claims 12 to 16, further comprising providing protection circuitry against power surges and spikes.

18. The method of claim 15, wherein the local power network comprises power cables within one of: an apartment, a dwelling, a building and a facility.

19. The method of claim 15 or claim 18, comprising positioning the head end coupler at or proximal to a power supply point for the local power network to isolate communication signal traffic within the network from the general power grid.

20. The method of any one of claims 15, 18 and 19, further comprising coupling communication signals to and from the local power network at a plurality of points on the local power network.

21. The method of any one of claims 15 and 18 to 20, wherein the local power network is a load.

22. The method of any one of claims 15 and 18 to 20, wherein the local power network is a supply.

23. A power line communication system comprising: at least one communication device coupled to a local power network; and a directional coupler in accordance with any one of claims 1 to 11 , configured to secure communication signal transmission over the local power network. 24. A power line communication signal repeater comprising: a first primary winding between a first port and a central connection, for carrying electrical power and communication signals; at least one first communication signal carrying winding inductively coupled to the first primary winding in a communication frequency band and substantially isolated from the primary winding in a power frequency band; a second primary winding between the central connection and a second port, for carrying electrical power and communication signals; at least one second communication signal carrying winding inductively coupled to the second primary winding in a communication frequency band and substantially isolated from the primary winding in a power frequency band; a filter at the central connection for minimising communication signal flow through the central connection while permitting power flow through the central connection; means to amplify communication signals received at the at least one first communication signal carrying winding for insertion by the at least one second communication signal carrying winding, and to amplify data received at the at least one second communication signal carrying winding for insertion by the at least one first communication signal carrying winding. 25. The power line communication signal repeater of claim 24, wherein the filter is connected between the central connection and neutral.

26. The power line communication signal repeater of claim 25, wherein the filter comprises a pass band encompassing the communication frequency band, and a stop band encompassing the power frequency band. 27. The power line communication signal repeater of any one of claims 24 to 26 wherein a frequency band of the communication signals carried in the first primary winding overlaps or is substantially equal to a frequency band of the communication signals carried in the second primary winding.

28. A data router comprising the power line communication signal repeater of any one of claims 24 to 27.

29. A data signal conditioning device comprising the power line communication signal repeater of any one of claims 24 to 27.

30. A data signal condition monitor comprising the power line communication signal repeater of any one of claims 24 to 27. 31. A coupling device for coupling a data node to a power line communications network, the coupling device comprising: a primary winding in series between a first port and a second port, for carrying electrical power and for coupling communication signals; at least one communication signal carrying winding inductively coupled to the primary winding in a communication frequency band and substantially isolated from the primary winding in a power frequency band; and a filter at the first port for minimising flow of signal components outside the power frequency band through the first port, while permitting power flow through the first port.

32. The coupling device of claim 31, wherein a data node power supply is drawn from beyond the first port.

33. The coupling device of claim 31 or claim 32, wherein the filter is configured to minimise flow of signal components in a frequency band representative of anticipated noise sources.

34. The coupling device of claim 33 wherein the anticipated noise sources comprise switch mode power supply units.

35. The coupling device of any one of claims 31 to 34, wherein the filter is configured to minimise flow of signal components in a communications frequency band.

36. The coupling device of any one of claims 31 to 35, wherein the filter comprises a bandpass filter centred upon the power frequency and having stop bands for minimising flow of signal components outside the power frequency band.

37. The coupling device of any one of claims 31 to 35, wherein the filter comprises a lowpass filter having a cutoff frequency above the power frequency and having a stop bands for minimising flow of signal components outside the power frequency band. 38. A method of coupling a data node to a power line communications network, the method comprising: providing a primary winding in series between a first port and a second port, for carrying electrical power and for coupling communication signals; inductively coupling at least one communication signal carrying winding to the primary winding in a communication frequency band and substantially isolating the communication signal carrying winding from the primary winding in a power frequency band; and filtering the first port to minimise flow of signal components outside the power frequency band through the first port, and to allow power flow through the first port. 39. The method of claim 38, further comprising drawing a data node power supply from beyond the first port. 40. The method of claim 38 or claim 39, wherein the filtering minimises flow of signal components in a frequency band representative of anticipated noise sources.

41. The method of claim 40 wherein the anticipated noise sources comprise switch mode power supply units. 42. The method of any one of claims 38 to 41, wherein the filtering minimises flow of signal components in a communications frequency band.

43. The method of any one of claims 38 to 42, wherein the filtering comprises providing a bandpass filter centred upon the power frequency and having stop bands for minimising flow of signal components outside the power frequency band. 44. The method of any one of claims 38 to 43, wherein the filtering comprises providing a lowpass filter having a cutoff frequency above the power frequency and having a stop bands for minimising flow of signal components outside the power frequency band.