Abstract:
A system for decreasing high frequency (HF) radiation emission in a power line comprises a first transmitter configured to transmit a utility power signal over the power line. A second transmitter transmits a high frequency communication signal over the power line so as to provide a combined utility and high frequency signal. A plurality of modulators, each of which provides a differential output signal to at least two phases of the power line such that the same high frequency data signal is transmitted via at least two phases of the power transmission line in an out-of-phase arrangement.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to data communications, and more specifically to a broadband communication system employing power distribution and transmission lines.  
       BACKGROUND OF THE INVENTION  
       [0002]     Within the past few years a new mode of communicating data has been accomplished by employing existing power lines. This mode of communications is referred to as broadband over power lines (BOPL). BOPL allows power utility companies to utilize their backbone electric grid infrastructure to offer customers high speed telecommunications services. Thus, power utility companies can now provide continuous high speed Internet access by modest changes of their existing plant.  
         [0003]     Broadband over power line technology employs building, underground, and/or overhead power lines to conduct HF and VHF digital signals for allowing computers to connect to the Internet. The FCC views this technology as a competitive Internet access point, and the utilities view the technology as a means to use existing infrastructure to generate additional revenue from something other than power generation, transmission, and distribution.  
         [0004]     One important concern about transmission of high frequency signals over power lines is electromagnetic radiation from the power lines into already used frequency channels. More specifically, for high frequency signals, the power line may act as an antenna that is able to emanate electromagnetic radiation leading to a significant interference to over-the-air radio services.  
         [0005]     Under current FCC regulations, power transmission lines may emit signals having a power of up to 30 microvolts/meter at a distance of 30 meters from the source. However, such emission levels could easily interfere with other overlapping frequency channels, such as those used by the Amateur Radio Service. The problem with such interference is that it affects not only the Amateur Radio community, but also those who employ radio services using High Frequency (HF) spectrum.  
         [0006]     Thus, there is a need for an arrangement that can effectively overcome the problems arising from transmission of high frequency signals over power lines.  
       SUMMARY OF THE INVENTION  
       [0007]     In accordance with one embodiment of the invention high frequency signals are carried over an electric utility power line employing one or more phases plus a neutral wire with a voltage signal level kept at or near ground potential. High frequency data signals are fed into each line with a different phase in a balanced arrangement so as to minimize radiation.  
         [0008]     In accordance with another embodiment of the invention, high frequency signals are generated via an amplifier that provides a balanced output signal. As such the amplifier includes two output ports, each of which provides a signal, which is nominally 180 degrees out of phase with the other. The high frequency signals are then fed to corresponding phases of a power line via an isolating device. The isolating device allows the high frequency signal to be fed to the power line, while preventing the voltage signal on the power line to be fed to the amplifier.  
         [0009]     In accordance with another embodiment of the invention, the balanced feed is accomplished by employing two modulators or amplifiers, whose local oscillators are locked together 180 degrees out of phase. If the same modulation scheme is applied in both modulators or amplifiers, then their outputs taken together will be balanced.  
         [0010]     In accordance with other embodiments of the invention, other schemes to generate signals that are nominally 180 degrees out of phase may be employed, such as providing an infrared link, or a fiber link or a wire link between the modulators. Furthermore, the local oscillators may act in a master-slave configuration where the master sets the system phase and the slave locks to it. In accordance with yet another embodiment of the invention a master oscillator is provided, to which other local oscillators lock.  
         [0011]     The balanced feeding arrangement can be employed in accordance with another embodiment of the invention, between one of the voltage phases and the neutral phase. This and other embodiments of the invention will be explained in more detail in connection with the accompanied figures.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  illustrates a system that allows transmission of broadband signals over power lines in accordance with one embodiment of the invention.  
         [0013]      FIG. 2  illustrates a portion of a transmission line illustrated in  FIG. 1 , with a balanced feed arrangement for providing high frequency signals to three phases of a power transmission line in accordance with one embodiment of the invention.  
         [0014]      FIG. 3  illustrates a differential feeding arrangement for providing high frequency signal to a single phase of a power transmission line via a capacitive coupling in accordance with one embodiment of the invention.  
         [0015]      FIG. 4  illustrates a differential feeding arrangement for providing high frequency signal to a single phase of a power transmission line via an inductive coupling in accordance with one embodiment of the invention.  
         [0016]      FIG. 5  illustrates a differential feeding arrangement for providing high frequency signal to a power transmission line via two separate modulators being nominally 180 degrees out of phase with respect to each other.  
         [0017]      FIG. 6  illustrates a differential feeding arrangement for providing high frequency signal to a power transmission line via two modulators communicating via a wireless channel.  
         [0018]      FIG. 7  illustrates a differential feeding arrangement for providing high frequency signal to a power transmission line via a modulator having a differential output circuit.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]      FIG. 1  illustrates an electric distribution arrangement that is employed to carry high frequency communication signals. Typically, a generating station  12  provides transmission voltage signals to substations  14 . At a primary distribution phase  15 , substations  16  are in turn coupled to electric poles  20 , for directing a power line  18  towards end users. At a secondary distribution phase  18  the voltage signal is stepped down, for transmitting power to end user homes and offices.  
         [0020]     A backhaul network  22  is coupled to an Internet network  24  from one end and to the electric distribution system on the other end. Backhaul network  22  is coupled to a substation router  26 , which in turn is coupled to a utility line via a coupler  28 . Coupler  28  includes a differential high frequency signal feeder  30  as described in more detail in reference with  FIGS. 2-7  below. High frequency signal feeder  30  is configured to provide high frequency communication signals in a balanced arrangement, such that the signals provided to each phase of the power line are out of phase with respect to each other, preferably within 180 degrees.  
         [0021]     As such, backhaul network  22  provides Internet communication signals to the transmission lines, and ultimately to end user&#39;s  102  electric outlets. It is noted that the invention is not limited in scope in that respect and other high frequency signals such as those generated within voice networks  90  and other types of data networks  92  can be injected into the utility lines.  
         [0022]      FIG. 2  illustrates an electric pole  20  with a portion of the utility lines extending therefrom in accordance with one embodiment of the invention. As illustrated each utility line  40 ( a )- 40 ( d ) is configured to carry one phase of a three-phase power signal. For example line  40 ( a ) is configured to carry an active phase A signal, whereas lines  40 ( b ) and  40 ( c ) carry active phase B and phase C signals respectively. Finally, line  40 ( d ) is the neutral phase of the power transmission line, wherein the signal level is set to ground potential.  
         [0023]     High frequency data signals are fed to the power transmission lines via modulators  110 ,  114 ,  118  and  126  respectively. In accordance with one embodiment of the invention, these modulators are located within differential high frequency signal feeder  30 .  
         [0024]     It is noted that instead of modulators, high frequency amplifiers are employed in accordance with another embodiment of the invention. As such, it is appreciated by those skilled in the art that in connection with the description of the various embodiments of the invention, high frequency amplifiers and modulators are interchangeable.  
         [0025]     Modulator  110  includes two output ports, one of which is coupled to phase A of power transmission line via capacitor  112 . The other output port of modulator  110  is coupled to phase C of power transmission line via capacitor  126 . Modulator  110  provides two output signals, 180 degrees out of phase with respect to each other.  
         [0026]     Similarly, modulator  114  includes two output ports, one of which is coupled to phase A of power transmission line via capacitor  116 . The other output port of modulator  114  is coupled to phase B of power transmission line via capacitor  120 . Modulator  114  provides two output signals, 180 degrees out of phase with respect to each other.  
         [0027]     Finally, modulator  118  includes two output ports, one of which is coupled to phase B of power transmission line via capacitor  122 . The other output port of modulator  118  is coupled to phase C of power transmission line via capacitor  124 . Modulator  118  provides two output signals, 180 degrees out of phase with respect to each other.  
         [0028]     The use of the differential feeding arrangement in accordance with various embodiments of the present invention, substantially reduces the radiation emitted by the utility line  40  when carrying a high frequency HF communication signal.  
         [0029]      FIG. 3  illustrates another embodiment of the invention wherein a modulator  140  providing a differential output signal, provides a high frequency data, via capacitors  142  and  144 , to each phase of the transmission line, such as phase C and the neutral line respectively. The output data signals provided by the modulator is nominally 180 degrees out of phase with respect to each other. As such three separate modulators are employed each of which is feeding one phase of the transmission line and the neutral line.  
         [0030]      FIG. 4  illustrates a balanced feeding arrangement in accordance with another embodiment of the invention. Modulators  160  and  170  provide a nominal 180 degrees out of phase high frequency data signal. It is noted that modulators that provide a balanced output, such as  160  and  170 , employ the same modulation scheme. The output port of modulator  160  is coupled via an inductor  162  to one of the phase lines of the power transmission line, and the output port of modulator  170  is coupled via an inductor  172  to the neutral line. The phase of the output signals generated by modulators  160  and  170  are locked to remain nominally 180 degrees out of phase with respect to each other.  
         [0031]      FIG. 5  illustrates a balanced feeding arrangement in accordance with yet another embodiment of the invention. A local oscillator  202  is configured to provide a high frequency signal to modulator  192 . The output port of modulator  192  is coupled to one of the phase lines of the power transmission line as discussed above in connection with  FIGS. 1-4 . Similarly, a local oscillator  204  is configured to provide a high frequency signal to modulator  194 . The output port of modulator  194  is coupled to another one of the phase lines of the power transmission line as discussed above. A data signal source  190  is configured to provide data signals to each of the modulators. Local oscillators  202  and  204  are configured to remain nominally 180 degrees out of phase with respect to each other. As such the modulated data signal provided to the power transmission line includes an in-phase and a nominal 180 degrees out of phase component, wherein together substantially reduce the unintentional radiation generated by the high frequency data signals.  
         [0032]     In accordance with one embodiment of the invention, in order for the local oscillators to remain nominally 180 degrees out of phase, a master oscillator  210  provides a signal, to which both oscillators  202  and  204  are coupled in a master-slave arrangement. Alternatively, one of the local oscillators may act as a master oscillator and the other oscillator is configured to operate as a slave configuration.  
         [0033]      FIG. 6  illustrates one embodiment for providing a linking arrangement between the two modulators  192  and  194  illustrated in  FIG. 5 . Thus, modulator  192  communicates with modulator  194  to provide phase locking information for the local oscillators  202  and  204 . Furthermore, the data signal provided by data signal source  190  is also communicated via a communications channel set up between the two modulators. The communication channel in accordance with one embodiment of the invention is a wireless connection such as an Infrared connection or a radio link connection. As explained above, the output port of each of the modulators is coupled to one of the phase lines of the power transmission line.  
         [0034]      FIG. 7  illustrates a modulator  220  having a differential output port. As such, an output port of modulator  220  is couples to an amplifier  222  having an in-phase output port and an 180 degrees out-of-phase output port. The in-phase output port is coupled to a phase line of the power transmission line. The out-of-phase output port is coupled to a second phase line of the power transmission line via an infra red transmitter  224 , and an infra red receiver  226  coupled to a second amplifier  230 . In accordance with various embodiments of the invention, the infra red connection may be replaced by a fiber optic or a radio or a wired connection.  
         [0035]     It is noted that for all the embodiments described herein, even though the data signal is placed on the power transmission lines in a balanced manner, the data signal may be removed in an unbalanced manner, i.e., single ended, as there will be HF current flowing in any given phase.  
         [0036]     Furthermore, although the modulators described in connection with the above embodiments provide 180 degrees out of phase signals, the invention is not limited in scope in that respect. For example, the high frequency signals provided to the power line may be sufficiently out of phase to substantially reduce the electromagnetic radiation arising from the transmission of the high frequency data signal. The electromagnetic reduction is a function of line characteristics desired by the operator of the transmission line.  
         [0037]     Thus, in accordance to various embodiments of the invention, it is possible to reduce the radiation emitted from the transmission lines that carry high frequency communication signals. This is accomplished by providing a balanced output signal to various lines of the power transmission line.