Most systems use the HomePlug standard which provide

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Broadband Communications over Power Lines(PLC)

• By Marc C. Tarplee, Ph.D. N4UFP
• ARRL Technical Coordinator
• SC Section

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What is PLC?
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• PLC (also known as BPL) is a technique for
  sending high speed data through the medium
  voltage power distribution network
• The idea of sending data through the power
  distribution network is not new
• Utilities use LF for network control and
  telemetry (typically lt 0.200 MHz)
• Schools have used carrier current system for
  campus radio systems that operate in the AM
  band (0.530 1.700 MHz)
• What makes BPL different is that it uses
  frequencies between 2 and 80 MHz

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(No Transcript)
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2. Types of PLC
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• There are three major categories of PLC
• Access PLC uses electrical distribution lines,
  overhead or underground, to provide broadband
  Internet access to homes and businesses.
• This is currently in the developmental stage
• In-building PLC uses the electrical wiring within
  a building to network computers.
• Most systems use the HomePlug standard which
  provides protection for amateur frequencies
• Control PLC operates below 500 kHz, and is used
  by electric-utility companies to control their
  equipment using the power-lines as transmission
  lines.
• These systems are not a problem, although it is
  interesting to note that utilities successfully
  lobbied against an amateur VLF allocation,
  claiming that amateur transmissions could disrupt
  their communications.

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3. PLC Modulation Techniques
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Access PLC

• Access PLC systems are presently under
  development. Current systems use OFDM (orthogonal
  frequency division multiplexing) in combination
  with some type of PSK .
• Carrier frequencies can be between 2 and 30 MHz.
  
• No filtering provisions are made to protect other
  users of the HF/VHF spectrum
• Data throughput gt 10 Mb/sec

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HomePlug

• HomePlug uses a combination of OFDM (orthogonal
  frequency division multiplexing) and DQPSK
  (differential quadrature phase shift keying) to
  send data through power lines within the home.
• Carrier frequencies are between 4.5 and 21 MHz.
• The modem output has notches at 3.5, 7.0, 10.1,
  14.0, and 18.1 MHz to reduce interference to
  amateurs.
• Data throughput gt 10 Mb/sec

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HomePlug

• Software in the receiver continuously determines
  the transfer function of the medium and carrier
  frequencies are changed to use the best available
  spectrum.
• HomePlug signal power is spread over the entire
  4.5 21 MHz bandwidth as the carrier frequencies
  are changed.
• HomePlug signals can pass through a residential
  service entry panel with less than 10 dB loss.

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HomePlug Spectral Mask
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Control/Carrier Current PLC

• These use frequencies below 1.7 MHz.
• Carrier current AM signals 0.53 1.70 MHz
• LF telemetry/control signals used by utilities
  lt0.2 MHz
• Signals have narrow bandwidth ( lt 10 KHz) and
  have carrier frequencies below all amateur bands.
  
• These signals do not generally present serious
  interference problems to amateurs
• Data throughput ltlt 1 Mb/sec

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4. RFI from Access Line PLC
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• Tests involving PLC systems in Japan and Europe
  indicate that PLC can cause significant
  interference to other users of the HF spectrum.
• Medium voltage power distribution lines look very
  much like antennas at HF wavelengths.
• The next slide shows the far-field pattern of a
  328 ft (100 m) segment of a typical MV
  distibution line. The conductors are at a height
  of 10m (32 ft 10 in) and they are spaced 1.5 m
  (4ft 5in) apart. The load is assumed to be the
  primary of a neighborhood transformer, which is
  assumed to have an impedance of 10 j25 ohms.

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Elevation patterns for radiation from MV Power
LinesPerpendicular to Lines
Parallel to Lines
9 dBi
28 MHz 14 MHz 7 MHz 3.5 MHz 0.15 MHz
28 MHz 14 MHz 7 MHz 3.5 MHz 0.15 MHz
5 dBi
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• As might be expected, the power lines look like
  long wire antennas at HF, with some gain and a
  complex multi-lobed radiation pattern
• It is interesting to note that the signal
  transmitted from the power lines in the LF range
  (150 kHz) is less than 70 dbi in any direction.
• Utilities RFI experience in the LF range is no
  predictor of RFI problems in the HF range.
• Because overhead power lines run in all
  directions, the resultant field produced by the
  entire power distribution system should be more
  or less isotropic in the azimuthal plane.
• ARRL simulations indicate that a fully-deployed
  access line PLC system would raise the noise
  floor by 70 dB (9 s-units 16 dB)

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Japanese PLC RFI Study
Noise Floor

• These measurements were made at 7 MHz on a 96 km
  long path in Japan.
• PLC signals raised the noise field strength by 25
  dB

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Effect of PLC on HF Coverage
20 m Coverage with access PLC in neighborhood
20 m Coverage under normal conditions
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• ARRL PLC Video

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5. RFI from HomePlug PLC
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• HomePlug uses a spectral mask that provides 30 dB
  of filtering in the amateur HF bands.
• At current RF brightness levels of 80 dBm/Hz,
  HomePlug signals can cause interference to
  antennas (especially indoor) that run within 2
  3 m of household power lines.
• HomePlug signals can also leak into other
  households with lt 10 dB of attenuation, causing
  problems for all homeowners sharing a common
  transformer.

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6. What Can Be Done?
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• The FCC recently closed off comment on the PLC
  docket. Hundreds of amateurs did comment on the
  problems with PLC during the comment period.
• Measurements need to be made. If a utility is
  deploying PLC in your area, please make
  measurements of the noise. We need to show the
  FCC what the problems are.
• It is very likely that some form of PLC will be
  implemented the economic potential is to great.
  It is important for amateurs to help steer the
  implementation so that our frequencies are
  protected