Note: Descriptions are shown in the official language in which they were submitted.
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
Coupling Device for Providing a Communications Link for RF Broadband
Data Signals to a Power Line and Method for Installing Same
Field of the Invention
The invention relates generally to coupling of RF signals, in particular to a
device
for coupling broadband RF signals for transmission through power lines and a
method for
installing same.
Background of the Invention
In the past, the only information service provided to customers such as
businesses
1o or private households was a telephone line. With technological advances
more and more
information services are provided to customers such as cable television, alarm
connection, high speed Internet connection and so forth. In order to provide
all these
information services to customers each service provider has to run a dedicated
cable to
the premises of their customers. Each dedicated line is proprietary to the
service provider
and, therefore, has to be maintained by that service provider.
A significant expense in providing service to subscribers, is the physical
link to
the subscribers. Cable lines are often cut during gardening and other digging
activities.
Also, animals can break connections. There is a substantial expense in laying
the original
cables to the premise of each customer. Furthermore, an increasing number of
different
information services received by a customer require the installation of a
plurality of
physical links to the premise of a single customer.
In order to overcome these difficulties, it has been proposed to use a
wireless
communication system to provide all services. Unfortunately, this is generally
costly and
presents a plurality of drawbacks. Therefore, it is slow to gain wide
acceptance and is
even suffering difficulties in finding test areas.
1
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
One form of service that is provided in industrial nations to every household
is
electrical power. In areas serviced by a power company, an electrical
connection to each
household allows for power delivery. Further, the power lines are monitored
regularly
and are pole mounted or buried deep underground for safety.
For a power line to serve as a communications link transmitting high-speed
data a
device is needed for reliably coupling the high-speed data to the power line.
In addition
such a device has to be inexpensive, essentially maintenance free and easy to
install in
existing installations at a customer's premise with minimum interruption or
without
to interruption of the power supply to other neighboring premises in order to
compete with
contending technologies. Furthermore, such a device has to guarantee safety by
isolating
the communications function from the power supply function at the customer's
premise.
Several devices for coupling communications signals to a power line have been
proposed in the following references, which are hereby incorporated by
reference:
US Patent 4,142,178 issued Feb. 27, 1979 to Whyte et al.;
US Patent 5,864,284 issued Jan. 26, 1999 to Sanderson; and,
US Patent 6,040,759 issued Mar. 21, 2000 to Sanderson.
2o All these proposed devices are very complex in their structure requiring
maintenance and are expensive to manufacture. Furthermore, these devices are
difficult
to install requiring disconnecting supply to the power line prior to the
installation. Thus,
these devices defeat their purpose for providing an inexpensive communications
link to a
customer's premise that is easily installed.
It is, therefore, an object of the invention to overcome the drawbacks of the
prior
art and to provide a device for coupling RF broadband data signals to a power
line that is
inexpensive, and essentially maintenance free.
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
It is another object of the invention to provide a device for coupling RF
broadband data signals to a power line that can be installed at a customer's
premise
without disconnecting power to the power line.
It is further an object of the invention to provide a method for installing a
device
for coupling RF broadband data signals to a power line without disconnecting
power to
the power line during installation.
Summary of the Invention
to In order to overcome these and other limitations of the prior art, there is
provided
in accordance with the invention a coupling device for injecting and
extracting a RF
broadband data signal to and from a power line. The coupling device is
inexpensive to
manufacture, essentially maintenance free, and easy to install. In a preferred
embodiment
such a coupling device is installable absent a step of disconnecting power to
the power
15 line which provides power to a customer's premise. Therefore, power supply
to
neighboring premises served by the same power line is not interrupted during
installation.
In accordance with the invention there is provided a coupling device for
providing
a communications link for RF broadband data signals to a power line
comprising:
2o a first port for connection to a power line;
a high-pass filter element connected to the first port, the filter element
allowing
RF broadband data signals to pass while substantially attenuating low
frequency signals;
and,
a second port connected to the high-pass filter element for connection to a RF
25 broadband data signal line.
In accordance with the invention there is further provided a coupling device
for
providing a communications link for RF broadband data signals to a power line
comprising:
30 a first port for connection to a power line;
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
a high-pass filter element connected to the first port, the filter element
allowing
RF broadband data signals to pass while substantially attenuating low
frequency signals,
wherein the high-pass filter element is connected to the first port via a
cable having
shielding spaced from the core at a sufficient distance to effectively limit
noise resulting
from the cable shielding in order to permit extraction of a RF broadband
signal absent
substantial noise; and,
a second port connected to the high-pass filter element for connection to a RF
broadband data signal line.
to In accordance with the invention there is further provided a coupling
device for
providing a communications link for RF broadband data signals to a power line
comprising:
a first port for connection to a power line;
a high-pass filter element connected to the first port, the filter element
allowing
15 RF broadband data signals to pass while substantially attenuating low
frequency signals;
a second port connected to the high-pass filter element for connection to a RF
broadband data signal line;
a drain coil connected to the high-pass filter element and connected to
ground, the
drain coil providing grounding for low frequency signals but preventing the RF
20 broadband data signals from being grounded; and,
a protective device connected in parallel to the drain coil for protecting the
second
port and the drain coil.
According to an aspect of the invention there is provided a coupling device
for
25 providing a communications link for RF broadband data signals to a power
line
comprising:
a first port for connection to a power line;
a second port for connection to a power input line of a premise and
electrically
connected to the first port via a power passthrough for providing power to the
premise,
3o wherein the power passthrough comprises a cable having shielding spaced
from the core
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
at a sufficient distance to prevent substantial noise from occurring within
the RF
broadband data signal;
a high-pass filter element connected to the power passthrough, the filter
element
allowing RF broadband data signals to pass while substantially attenuating low
frequency
signals;
a third port connected to the high-pass filter element for connection to a RF
broadband data signal line;
a ground terminal for connection to ground;
a drain coil connected to the high-pass filter element and connected to the
ground
1o terminal, the drain coil providing grounding for low frequency signals but
preventing the
RF broadband data signals from being grounded; and,
a protective device connected in parallel to the drain coil for protecting the
third
port and the drain coil.
15 According to another aspect of the invention there is provided a method for
installing a coupling device for providing a communications link for RF
broadband data
signals to a power line while the power line is provided with a power signal,
the method
comprising the steps of:
first connecting a ground terminal of the coupling device to a ground terminal
2o connected to a ground and connecting a port of the coupling device for
connection to a
RF broadband data signal line to a same;
second connecting a port of the coupling device for connection to a power
input
line of a premise to a same; and,
third connecting a port of the coupling device for connection to a power line
to
25 the power line comprising a power signal.
Brief Description of the Drawings
A description of the invention will now be provided with reference to the
attached
drawings in which:
3o Figure 1 is a schematic block diagram of a coupling device according to the
invention;
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
Figure 2 is a simplified block diagram of a another embodiment of a coupling
device
according to the invention;
Figure 3 is a simplified diagram illustrating a cross section of a power cable
used in the
coupling device according to the invention;
Figure 4a is a simplified block diagram illustrating an installation of the
coupling device
according to the invention;
Figure 4b is a simplified block diagram illustrating another installation of
the coupling
device according to the invention;
Figure 4c is a simplified block diagram illustrating yet another installation
of the
1o coupling device according to the invention; and,
Figure 5 is a simplified flow diagram of a method according to the invention
for
installing the coupling device.
Detailed Description of the Invention
15 Referring to Fig. 1 a coupling device 100 according to the invention for
providing
a communications link for RF broadband data signals to a power line is shown.
In the
following the device is described for installation at a customer's premise, i.
e. connected
to a distribution power network operating at medium or low voltage for
coupling data
signals in a frequency range of approximately 1 MHz to 40 MHz. As is obvious
to a
2o person of skill in the art, the device is described in connection with this
application for
simplicity but is not limited thereto. It is evident that the concept of this
device is also
operable in applications operating at higher voltage and/or higher data signal
frequencies,
for example, bypassing transformers between high voltage power lines and
medium
voltage power lines in a power supply network.
The coupling device 100 comprises a first port 102 for providing a connection
to a
power line providing electrical power to a customer's premise, a second port
104 for
providing a connection to a customer's RF broadband data signal line and a
ground
terminal 106 for providing a connection to a ground. The coupling device 100
further
comprises a coupling circuit housed in a grounded housing 108 as shown in Fig.
1.
Optionally, the housing 108 is not grounded, but use of this should be
restricted to
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
coupling devices which are pole mounted, installed in substations, installed
in service
entrances or installed inside transformer enclosures for safety reasons. In
other
applications the housing of the coupling device should be safe to touch. The
coupling
circuit comprises a high-pass filter element 108 such as a coupling capacitor
that is
connected at one end to the port 102. The filter element 110 allows RF
broadband data
signals to pass while substantially attenuating low frequency signals. The
other end of the
filter element 110 is connected to the second port 104 for providing extracted
RF
broadband data signals to the customer's data signal network and for receiving
RF
broadband data signals from the customer's network and for coupling onto the
power line
1o via the port 102. The other end of the filter element 110 is connected to
the ground
terminal 106 via a protective device 112 and a drain coil 114 connected in
parallel. The
protective device 112 provides protection for the drain coil 114 and the data
signal line -
second port 104 - from power surges induced, for example, by a lightning
strike into the
power line. For coupling of high frequency data signals a spark gap is
preferably used as
15 protective device 112 for having substantially no capacitance that could
have an impact
on the high frequency data signal. The drain coil 114, for example, an
inductor, provides
grounding for low frequency signals such as the power frequency component but
prevents the high frequency data signal from being grounded. Shielding of the
RF data
signal line is connected to the ground terminal at the second port 104.
Optionally, the
2o data signal line - second port 104 - is also provided with a protective
device such as a
spark gap interposed between the data signal line and the ground terminal to
enhance
safety for the data signal line. The coupling device according to the
invention provides
coupling of analog data signals as well as digital signals for transmission
via power lines.
25 A significant application of the coupling device according to the invention
is to
efficiently couple RF broadband data signals for distribution via a power
line, reaching
customers of information service providers. The coupling devices are installed
at a
customer's premise for coupling a RF broadband data signal line to the
distribution power
line. Another application of the coupling device is installation to bypass
transformers in
3o the distribution power line. The coupling device provides for these
applications a low
impedance coupling means for RF broadband data signals. Preferably, the
coupling
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
device has minimal insertion loss over the operating bandwidth to ensure
overall system
performance over inherently poor S/N (signal to noise) power lines.
Therefore, the coupling device according to the invention has to efficiently
couple
RF broadband data signals in a frequency range of approximately 1 MHz to 40
MHz
transmitted via medium voltage power lines. Most prior art systems pass lower
frequency
signals of 20KHz to SOOKHz thereby avoiding many of the problems encountered
in
higher frequency applications. To pass higher frequencies, a self-resonant
frequency of
the filter element 110 has to be very high, to ensure the least possible
signal attenuation
to over the frequency range to be passed. The inductance value of the drain
coil is
appropriately selected to avoid substantial attenuation of the radio frequency
signals and
provide a virtual ground for the coupling circuit at power frequency -
normally 50 Hz or
60 Hz. The coupling circuit - primarily the filter element 110 is (PD) partial-
discharge
free, i. e. less than 10 pC at maximum operating voltage phase to ground.
Unless the
connections are free of internal discharges the service life is reduced due to
PD based
aging. When these limits are not met the data signal quality is substantially
reduced due
to high frequency signal interference or the coupling circuit is non-
functional. Connection
methodology and external connection geometry are considerations for design and
analysis.
In order to provide a partial discharge free and a substantially maintenance
free
coupling device insulation systems for use with the invention include
substantially inert
gases such as SF6 or Nitrogen, liquids such as insulating oils, or a solid
dielectric
insulation system. Other embodiments include vacuum and/or pressure
impregnation of
capacitors, a resin molded structure and the use of ceramic or silicone rubber
coatings,
protective sheds, covers, etc.
In another embodiment of a coupling device 200 according to the invention
shown in Fig. 2 the coupling circuit further comprises an impedance matching
circuit 201
comprising a transformer 202 and a coupling capacitor 204. The combination of
the
characteristics of the transformer 202 and the coupling capacitor 204 allows
matching of
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
the coupling circuit impedance with the impedance of the customer's data
signal network.
This provides an optimal data signal having the least attenuation. Preferably,
the
impedance matching circuit is easily adjustable or comprises an easily
removable module
inserted in the housing 108. This allows easy and quick adjustment to a
customer's data
network impedance either on site during installation or before delivery of the
coupling
device.
In the past, attempts at extracting RF broadband signals from power lines have
resulted in signals that are too noisy for most uses. Therefore, these
approaches have not
1o been successful and no suitable means for extracting a RF broadband signal
from a power
line are known. The inventor has found that much of the noise within the
extracted RF
broadband signals emanates from cabling within the extraction device.
Therefore, the adequate control of electrical stresses in the cables and
connections
15 is necessary for the successful implementation of the invention.
Typical distribution voltage or high voltage power cables are not well suited
for
use in devices for coupling a RF broadband signal. According to the invention
a cable as
shown in Fig. 3 is used having a core 302 and a neutral shielding 304, wherein
the neutral
2o shielding 304 is spaced from the core 302 a sufficient distance to prevent
substantial
noise from occurring within the RF broadband signal.
Referring to Figs. 4a to 4c, different embodiments show installation of the
coupling device according to the invention. The coupling device 402 shown in
Fig. 4a
25 comprises one input port 404 for connecting to a power line. As
illustrated, the coupling
device is connected to the power line - transformer - via port 405 of feedthru
insert 406
connected to the transformer 408. High voltage power is provided to the
transformer via
port 407. The coupling device is grounded by grounding means 410 such as a
grounding
bracket mounted to a grounding bar 411. For safe operation the coupling device
must be
3o connected to a ground. For applications other than pole mounted devices the
housing and
connections must be safe to touch, i. e. connected to a ground. The housing,
in order to be
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
properly grounded, is preferably anchored to a ground terminal by a bolt. A RF
broadband data signal connection is provided by port 412. This type of
installation is
preferably used for test purposes. The coupling device 403, shown in Fig. 4b
comprises a
power passthrough 414 connected to the coupling device 403. Port 416 of the
power
passthrough 414 is connected to transformer 408 or, alternatively, to a
distribution power
line. Port 416 is connected to the transformer via a cable as shown in Fig. 4b
or,
alternatively, is directly connected to the transformer 408. Port 418 is
connected to the
high power line. The coupling device is grounded via grounding connection 410.
An
extracted RF broadband data signal is provided via port 412. The power
passthrough 414
1o is connected to the coupling device 403 via a flexible power cable
facilitating installation
in confined spaces or, alternatively is integrated in the housing of the
coupling device, as
shown in Fig. 4c. Thus, a coupling device as shown in Figs. 4b and 4c is
installable and
removable absent further components.
15 The coupling device according to the invention allows installation for both
overhead and underground power lines. In installations for underground power
lines the
coupling device can be installed within power transformer enclosures.
The embodiments shown in Fig. 4b and 4c allow installation of the coupling
2o device to a "live" underground power line. The method according to the
invention for
installing the coupling device is illustrated in the simplified flow diagram
of Fig. 5. First
the coupling device is grounded by connecting the ground terminal 410 of the
device 403
to an existing grounding terminal connected to ground. Then port 412 is
connected to a
port of a customer's RF broadband data signal network. Alternatively, the port
412 is
25 connected first and then the ground terminal 410. After these steps are
performed the
power supply to the customer's premise is reconnected by first connecting port
416 of the
device to a port for feeding power into the customer's premise and then
connecting port
418 to the power line. Alternatively, but not preferably, port 418 is
connected first. For
safety reasons it is essential that the grounding terminal be connected to an
existing
30 ground terminal before connecting to the live power line. Preferably, a
coupling device
comprising a housing connected to the ground terminal is used for providing a
device that
to
CA 02346208 2001-05-02
Doc. 102-O1 CA(3) Patent
is safe to touch. This method allows installation of the coupling device with
minimum
interruption of the power supply to neighboring premises. However, it is
preferred that
coupling devices for connecting to overhead power lines do not support this
method of
installation with live power lines in order to protect installation personnel
from potential
electrocution.
Numerous other embodiments of the invention will be apparent to persons
skilled
in the art without departing from the spirit and scope of the invention as
defined in the
appended claims.
to
11
