Possible Impact of VDSL on Stations Operating in the Amateur Radio Service Ed Hare, W1RFI ARRL Labor

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Possible Impact of VDSL on Stations Operating in
the Amateur Radio ServiceEd Hare, W1RFIARRL
Laboratory Manager225 Main StNewington,CT
06111w1rfi_at_arrl.org860-594-0318
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Part 15

• Absolute Maximum Limits
• Unintentional Emitters
• Non-interference
• Manufacturer responsible for FCC authorization
  and maximum limits
• Operator responsible for harmful interference
• Both are important to mitigate possible harmful
  interference

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Unintentional Emitter Emissions

• Radiated emissions above 30 MHz
• Conducted emissions below 30 MHz
• Good engineering practice
• Carrier-current devices must meet intentional
  emissions limits 3 installations
• Meeting the intentional emissions limits on HF is
  good engineering practice

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Intentional Radiator Radiated Emissions Limits -
HF

• Sec 15.209
• 1.705-30.0 MHz 30 uV/m at 30 meters
• This should protect users of the spectrum against
  interference, yes?

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No!

• If the absolute emissions limits were set to
  offer unconditional protection to all radio
  services, the permitted levels would be
  unworkably low
• Amateur Radio Service, by design, uses very
  sensitive equipment and weak signals
• The legal limit will result in a strong signal
  to nearby Amateur HF installations
• On 3.5 MHz, a half-wave dipole placed in a 30
  uV/m field will receive a 86.4 dBW signal (338
  microvolts across 50 ohms)
• To hams, this is S916 dB clearly harmful
  interference to typical amateur communications!
• Harmful interference at even greater distances
  than the compliance distance is likely
• The absolute limits are not enough to prevent
  interference to nearby receivers

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Harmful Interference

• The repeated disruption of radio communications
• Merely hearing a signal is NOT harmful
  interference
• 30 uV/m at 30 m works somewhat well for discrete
  signals
• If from broadband device, however, will interfere
  with entire band(s)!
• 30 uV/m works somewhat well for isolated sources
• If from VDSL, interference potential exists for
  occur for entire length of wiring in areas where
  VDSL is deployed!

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A Case History Wireless Modem Jacks

• Carrier-current devices that use residential
  electrical wiring to couple modem signals between
  a computer and a remote telephone connection
• Phonex model PX-421 designed to operate on 3.53
  MHz
• These were purchased in volume by TCI Cable and
  installed in conjuction with their digital cable
  systems
• Widespread S9 levels signals and harmful
  interference
• Phonex responded promptly, redesigned product
• TCI, now ATT still in midst of system-wide
  recall!
• Costs?

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What Can Be Expected from VDSL?

• Better scenario than power lines and electrical
  wiring
• Phone system reasonably well balanced at audio
• At HF? 20 dB to 30 dB balance typical?

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Amateur HF stations

• Bands at 1.8, 3.5, 7.0, 10.1, 14.0, 18.1, 21.0,
  24.8 and 28.0 MHz
• Receiver sensitivity 135 dBm
• Ambient noise levels 125 dBm
• Antenna gain 2.14 dBi (F.S) on 3.5 Mhz
• Antenna gain 7.5 dBi (F.S) on 14-30 MHz

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Balance

• EZNEC 3.1 used to model 50 feet of simple phone
  wiring (uses NEC-4, written by Lawrence Livermore
  National Laboratories)
• Terminated in 100 ohms j0
• Fed with two sources, one on each wire, 180
  degrees out of phase, with 20, 25 and 30 dB of
  balance
• Showed gain of 16 dBi to 26.4 dBi
• Real-world installations bigger radiators, but
  more loads on line
• Correctable defects

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Balance

• 20 dB -16.8 dBi
• 25 dB -21.8 dBi
• 30 dB -26.4 dBi
• Will use 21.8 dBi for following calculations

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Frequency 3.5 MHzReceiver bandwidth 2500
HzTransmit power in 1 Hz -50 dBm/HzTransmit
power in 2500 Hz -16.0 dBmTelephone-wiring
antenna gain -21.8 dBiReceive antenna gain
2.14 dBiDistance to receiver 0.03
kmFree-space pathloss -12.9 dbE-field
estimate in 30 kHz 140.8 uV/m peakReceive
Noise Figure 24 dB (includes external
noise)Calculated receive system sensitivity
-116.0 dBmReceived noise in receiver bandwidth
-48.6 dBm peakReceived noise in receiver
bandwidth S9 24.4 dBReceive system noise
floor increase in dB 67.4 dB
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Frequency 14 MHzReceiver bandwidth 2500
HzTransmit power in 1 Hz -50 dBm/HzTransmit
power in 2500 Hz -16.0 dBmTelephone-wiring
antenna gain -21.8 dBiReceive antenna gain
7.5 dBiDistance to receiver 0.03 kmFree-space
pathloss -24.9 dBE-field estimate in 30 kHz
140.8 uV/m peakReceive Noise Figure 24 dB
(includes external noise)Calculated receive
system sensitivity -116.0 dBmReceived noise
in receiver bandwidth -55.2 dBm peakReceived
noise in receiver bandwidth S9 17.8
dBReceive system noise floor increase in dB
60.8 dB
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Phoenix VDSL testing
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Conclusions

• Pre-standard system, but approximately 50 dBm/Hz
• Underground wiring, relatively new homes
• No VDSL signals detected except near one
  neighborhood hub just audible
• Other noises
• In areas of underground wiring, notching not
  needed
• However, this should NOT be extrapolated to
  determine that notching is not needed under other
  circumstances!

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HPNA
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HPNA
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HomePlug Final Specification
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Industry Measurements of Interference Potential?

• In general, industry has not made measurements of
  interference to other services
• Such measurements, made by Amateur Radio in
  other, similar disciplines show interference
  potential
• In all cases where industry groups have conducted
  joint studies with ARRL, they have chosen to
  include spectral masks in their industry
  standards or specifications
• To date, no widespread interference from
  protected products

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What is Needed?

• Based on modeling and calculations, -50 dBm/Hz
  will probably result in harmful interference with
  overhead wiring and older homes
• Amateur Radio vs other services?
• These models not exact, but demonstrate clearly
  the need for further study
• ARRL wants to participate in field studies,
  especially any near New England, but I will
  travel!

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What Does ARRL Want to Accomplish?

• Participate in field studies
• Protection to 80 dBm/Hz in ham bands
• Such notches will exist naturally in residential
  telephone wiring, so product must be robust
  enough to function with small segments of
  frequency band attenuated
• Advisory language in standard about harmful
  interference, the need to use notches when needed
  and the need for manufacturers to include such
  advisory information in their product literature
• Not necessary to use filtering HPNA standard
  achieves this level of protection by not using
  OFDM carriers in the ham bands.
• This will take care of MOST cases of harmful
  interference. Remainder are correctable defects
  or can be addressed on a case-by-case basis
• If frequencies not used, additional filtering can
  be added
• Why waste a good notch? Other services?

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More InformationEd Hare, W1RFIARRL Laboratory
Manager225 Main StNewington,CT
06111w1rfi_at_arrl.org860-594-0318

• http//www.arrl.org/ehare/rfi/vdsl/vdsl.html
• http//www.arrl.org/tis/info/part15.html

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