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Part 15

Possible Impact of VDSL on Stations Operating in the Amateur Radio Service Ed Hare, W1RFI ARRL Laboratory Manager 225 Main St Newington,CT 06111 w1rfi@arrl.org 860-594-0318. Part 15. Absolute Maximum Limits Unintentional Emitters Non-interference

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Part 15

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  1. Possible Impact of VDSL on Stations Operating in the Amateur Radio ServiceEd Hare, W1RFIARRL Laboratory Manager225 Main StNewington,CT 06111w1rfi@arrl.org860-594-0318

  2. 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

  3. 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

  4. 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?

  5. 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

  6. 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!

  7. 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?

  8. 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?

  9. 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

  10. 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

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

  12. 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

  13. 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

  14. Phoenix VDSL testing

  15. 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!

  16. HPNA

  17. HPNA

  18. HomePlug – Final Specification

  19. 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

  20. 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!

  21. 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?

  22. More InformationEd 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

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