Possible Impact of VDSL on Stations Operating in the Amateur Radio Service

Ed Hare, W1RFIARRL Laboratory Manager

225 Main StNewington,CT 06111

w1rfi@arrl.org860-594-0318

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

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

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?

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 S9+16 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

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!

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 AT&T still in midst of system-wide recall!• Costs?

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?

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

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

Balance

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

calculations

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

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

Phoenix VDSL testing

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!

HPNA

HPNA

HomePlug – Final Specification40

100

MASKy

300 y mhz0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

100

95

90

85

80

75

70

65

60

55

50

45

40

FREQUENCY MHZ

POW

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BM

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Z

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

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!

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?

More Information

Ed Hare, W1RFIARRL Laboratory Manager225 Main StNewington,CT 06111w1rfi@arrl.org860-594-0318

• http://www.arrl.org/~ehare/rfi/vdsl/vdsl.html

• http://www.arrl.org/tis/info/part15.html