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Not to be used outside the RA TWG on VDSL without written permission from RA and BT RA Technical Working Group on VDSL & PLT Compatibility With Radio Services.

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Presentation on theme: "Not to be used outside the RA TWG on VDSL without written permission from RA and BT RA Technical Working Group on VDSL & PLT Compatibility With Radio Services."— Presentation transcript:

1 Not to be used outside the RA TWG on VDSL without written permission from RA and BT RA Technical Working Group on VDSL & PLT Compatibility With Radio Services VDSL Emission Measurement Programme Status Report to the TWG 3rd July 2001 Colin Wooff (RA3/RTCG)

2 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 2: The RA VDSL Measurement Programme Test schedule agreed by TWG on 30th March Conducted by RTCG using BT test facilities Planned in three separate phases Each phase lasted one week –Week 1:2-6 April –Week 2: May –Week 3: June Separate work undertaken by radio users –Mod / DERA:during weeks 2&3 –RSGB:during weeks 2&3 –BBC:during week 3

3 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 3: The RA VDSL Measurement Programme Today’s presentation: –Programme objectives –Measurement objectives –Test procedures –Swept measurements –Results –Observations

4 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 4: The RA VDSL Measurement Programme Overall programme objectives (TWG(01)06) –Discover range of radiated emission levels –Assess likely effects on nearby radio systems –Provide data to predict cumulative effects – Inform UK input to international fora

5 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 5: The RA VDSL Measurement Programme Measurement objectives: –Characterize lines ( BT) –Characterize VDSL modems (BT) –Determine radiated emission levels –Correlate line balance with emission levels –Assess factors that may effect emission levels –Measure emission level attenuation with distance

6 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 6: BT Adastral Park - 4 Acre Test Site (BT)

7 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 7: The RA VDSL Measurement Programme Line characteristics (supplied by BT) –D.C. Loop resistance –Insertion loss –Balance

8 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 8: Line Insertion Loss & Loop Resistance (BT)

9 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 9: Line Balance Characteristic (BT)

10 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 10: Modem Specification (BT) Highly integrated prototype Built to ETSI TS Conforms to 998 VDSL plan Broadband SCM 25 M bit/s downstream 8 M bit/s upstream Max PSD: -60dbm / Hz Power back off facility (upstream)

11 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 11: Modem Output Spectrum (BT) System Clock (25.96MHz) 1/2 System Clock (12.98MHz) Out of band interference

12 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 12: Week 1 Measurements Spot Frequency Radiated Emissions Measurements made on all 6 available lines Each line has 2 wire pairs - 12 circuits in total All 12 circuits nominally 260 metres long between the downstream and upstream VDSL modems

13 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 13: Measurement Locations - Plan View (BT)

14 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 14: Loop Antenna Position - ‘Customer End’ (Near the NTP and Modem)

15 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 15: Test Equipment Configuration Spot Frequency Measurements U of H tuned loop antenna - used to achieve a lower measuring system noise floor 1 metre spacing from dropwire CISPR receiver - 9kHz BW - peak detector Two ‘quiet’ test frequencies within each of the 4 VDSL deployment bands

16 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 16: VDSL Emission Levels at 1 m Spacing (See Handout for More Detail)

17 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 17: Observations Spot Frequency Emission Measurements All emissions were above measuring system noise floor Larger than expected variation between emissions from the 2 pairs in a single dropwire Little apparent correlation between emissions from different routes

18 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 18: Swept Measurements - VDSL Emissions (Normal Operation)

19 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 19: VDSL Emissions - Split Pair Drop Wire (FAULT Condition)

20 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 20: Observations: Swept Frequency Emission Measurements The significant variability in the VDSL frequency v emission profile is easily seen High measuring system noise floor using this method with a standard CISPR loop antenna would prevent a complete analysis of the 1, 3 and 10 metre VDSL field strength attenuation

21 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 21: Field Attenuation With Distance Spot Frequency Measurements Agreed value needed: To correct emission measurements made at one distance to limits specified at another distance To assess potential interference effects at distances other than those used for emission measurements To provide data for cumulative emission studies

22 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 22: 1 to 3 & 10 Metre Field Attenuation Loop Antenna - Vertical Dropwire

23 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 23: 1 to 3 / 10 Metre Field Attenuation Loop Antenna - Vertical Dropwire

24 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 24: 1 to 3 Metre Field Attenuation Loop Antenna - Horizontal Dropwire

25 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 25: 1 & 3 Metre Loop to 10m Dipole Attenuation Measurements - Horizontal Dropwire

26 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 26: 1 & 3 Metre Loop to 10m Dipole Relative Field From Horizontal Dropwire

27 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 27: Observations - Field Attenuation Results Large variations at different frequencies 3 m loop to 10 m dipole values larger than predicted by the 20 log d1/d2 formula Close-in loop measurements seem unlikely to be suitable for predicting far field effects. Spot frequency measurement do not provide sufficient data to facilitate proper analysis

28 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 28: Other Findings No effect on VDSL emission levels observed when the POTS circuit was disconnected at both ends of the line No effect on VDSL emission levels observed due to the simultaneous operation of the POTS circuit

29 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 29: Conclusions After First Week Need to explain the variability of VDSL emission results before declaring them as valid Statistical analysis based on a large number of swept measurements look more promising High power broadband noise signal with flat PSD necessary to measure field attenuation with balanced lines

30 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 30: Week 2 Measurements High Power Broadband Tests To examine resonances in VDSL lines without undue intrusion from ambient signals To facilitate the analysis of field attenuation with distance To allow user group assessments at larger separation distances where emissions can be scaled down to VDSL PSD levels

31 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 31: High Power Broadband Tests Equipment for Swept Measurements –Broadband Guassian white noise generator- with high power amplifier - giving a launch PSD of up to - 25 dBm/Hz –High power balun for connection to lines –High power balanced load resistor –CISPR magnetic loop antenna –CISPR measuring receiver with fast scanning and data storage facility

32 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 32: Line Resonance and Parasitic Effects High Power Broadband Source - NOT VDSL (Unbalanced to Increase Common Mode Current)

33 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 33: Basic Observations on Line Resonances Current nodes can be expected at half wavelength intervals related to the electrical length of the line in respect of the common mode standing wave Parasitic effects can be observed at the BT site by varying the lengths of the nominally identical circuits which are closely coupled within the 20 pair underground feed cable

34 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 34: Consequences of the Resonance Effects Common mode terminations, line parasitic and proximity effects may all conspire to vary the position of the current nodes in a totally unpredictable way Single frequency magnetic field emission measurements are likely to be misleading in these circumstances

35 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 35: Field Attenuation With Distance High Power Broadband Source - NOT VDSL (Balanced Line)

36 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 36: Observations - Field Attenuation Line resonance effects demonstrate the difficulty of achieving consistent results based on this measurement technique It can be seen that current nodes vary in frequency at the 3 measuring distances which may be due to the proximity effect of the loop or inherent when using a directional antenna near a distributed source radiator

37 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 37: Week 3 - VDSL Emissions ‘in the Home’ A fundamental issue in relation to HF broadcast reception Important to understand how installation variables may affect emission levels Necessary to know by how much the most common installation FAULT will increase emission levels

38 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 38: User Premises VDSL Emissions BT ‘Classic’ Installation - With Splitter

39 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 39: User Premises VDSL Emissions ‘Self Install’ Installation - No Splitter (BT is not currently contemplating self-install VDSL)

40 Not to be used outside the RA TWG on VDSL without written permission from RA and BT 40: Initial Conclusions on VDSL Emissions VDSL emission levels ‘in the home’ with a splitter and CAT 5 wiring installed are similar to those measured on the incoming dropwire outside Self install VDSL without a splitter will show significantly higher emissions The ‘split pair’ fault under which VDSL may still operate normally gives the highest emission levels


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