Radiocommunications Agency - VDSL / PLT TWG Meeting - Whyteleafe Surrey - 30 march 2001
Assessment of Radiated Emissions from VDSL at BT Adastral Park 4 Acre Site
1.
Introduction
The BT document “VDSL Emissions – Draft Practical Measurement Plan”, prepared
for submission to the first meeting of the Technical Working Group on 30th March
2001, proposes a series of measurements at the BT Adastral Park facilities to
determine the radio frequency emissions from a number of purposely constructed,
but representative, VDSL enabled lines.
This paper is intended to complement the BT proposals and sets out the detail for the
VDSL emission measurements, to be carried out at the BT “4 Acre Test Site” in a
series of three separate one week periods in April; May and June 2001 respectively.
It is the intention of the Radiocommunications Agency (RA) to ensure that as far as is
practical, both the test configuration and the potential interference scenarios to be
investigated will be as representative as possible of typical situations that would
follow VDSL deployment in the UK. It is the Agency’s wish therefore that members of
the Technical Working Group will feel free to contribute and provide comment on
these proposals.
2.
Objectives
The purpose of the VDSL measurement programme is to:
2.1
discover the range of radiated emission levels, likely to be encountered in
practice, at 1; 3 and 10 metres respectively from a representative POTS
telephone loop comprising unscreened twisted pair cables where base band
telephony signals have been overlaid with high frequency VDSL signals from
standards compliant VDSL Modems;
2.2
utilise the information gathered from measurements of single representative
POTS loops to predict the nature and extent of cumulative emissions from
multiple VDSL circuits;
2.3
determine by both objective and subjective assessment, the range of likely
effects that the measured or calculated VDSL emissions may have on
representative radio communications systems located at various distances
from VDSL circuits;
2.4
inform UK, European and International standards bodies who may be engaged
in deriving suitable radiated emission limits for the protection of radio
communications services from undue interference caused by radiated
emissions from VDSL networks.
3.
Measurement Procedures
It is intended to utilise, verify and if necessary refine the measurement procedures
previously proposed in Part C of the February 2000 Draft of MPT 1570.
Source: Radiocommunications Agency RTCG Whyteleafe
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Radiocommunications Agency - VDSL / PLT TWG Meeting - Whyteleafe Surrey - 30 march 2001
(NB: Part C is not included in the current (April 2000) version of MPT1570)
In addition, where they may differ, it is also intended to test the measurement
procedures contained in the joint RA/RegTP document ‘In-Situ Measurement
Procedures and Proposed limits for Radio Disturbance Emissions from
Telecommunication Networks ’. The latter was submitted jointly by the German and
UK administrations to CEPT/ERC SE PT SE35 under reference SE35(00)29, for
consideration as a basis for a standard and inclusion within a first draft of a proposed
ERC Recommendation.
Details of the measurements to be undertaken are set out in three annexes to this
paper which provide a draft workplan for each of the three proposed one-week
periods of site measurements. These three periods will cover respectively:
 1st week:
 2nd week:
 3rd week:
test site and VDSL equipment characterisation (annex A)
broadcasting and amateur services
(annex B)
military and other government services
(annex C)
4.
Specification for POTS Loop & VDSL Equipment Under Test
4.1
Configuration of Test Loops (see figs. 1 and 2 in BT measurement plan )
A small network of up to 12 twisted pair test loops comprising working POTS lines
constructed with standard BT specification wiring, network terminating equipment and
VDSL splitters. The loop lengths will be capable of adjustment up to the maximum
intended VDSL deployment distance of [1 km]. To facilitate radiated emission
measurement, the loops will include a standard depth [1 metre] underground section
as well as standard height [6 metre] overhead sections at one end to represent
typical customer drops. The test loops will be capable of being energised individually
or on a group basis where it is intended to assess variations between apparently
identical loops or to determine any cumulative emission effects.
4.2
VDSL Test Signals
VDSL signals from standards compliant [998] VDSL Modems will be overlaid on to
working POTS lines. Ingress testing using a standard amateur radio transmitter may
also be undertaken subject to sufficient time being available. A full bandwidth VDSL
[video] signal and suitable receiving apparatus will therefore be available to facilitate
visual observation of any subjective effects in addition to the measurement of [raw]
Bit Error Rate.
4.3
Loop Integrity Tests
In addition to the normal loop length and loop resistance parameters, it is intended to
characterise each POTS loop for balance about earth within the VDSL frequency
spectrum. This information will be recorded and presented as the test loop
specification. With the VDSL modems operational, measurements of differential and
common mode current will be recorded to accompany each radiated emission
measurement.
Source: Radiocommunications Agency RTCG Whyteleafe
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Radiocommunications Agency - VDSL / PLT TWG Meeting - Whyteleafe Surrey - 30 march 2001
5.
TEST EQUIPMENT
5.1
Loop integrity Tests
Network analysers, precision measuring baluns and loop test equipment
specific to BT.
Calibrated CISPR current clamps.
5.2
Radiated Emission Measurements
5.2.1 Receiver:
A calibrated CISPR measuring receiver fitted with Peak,
Average and Quasi-Peak detectors and selectable 200 Hz or 9 kHz IF
bandwidths.
5.2.2 Magnetic Field Antennas: A plane wave calibrated, CISPR magnetic
loop antenna having an H field Antenna Factor of – 31.5 dB S/m giving
a plane wave E Field Antenna factor of 20 dB/m.
A set of 3, high sensitivity, calibrated magnetic loop antennas having
Antenna Factors approximately 25 dB lower than the standard CISPR
loop antenna.
5.2.3 Electric Field Antennas: A plane wave calibrated CISPR E Field Rod
Antenna having a plane wave E Field Antenna factor of 20 dB/m.
[A plane wave calibrated, short active dipole antenna with E Field
Antenna factor of 20 dB/m.]
A high sensitivity, plane wave calibrated, E Field rod antenna.
(Antenna Factor TBA)
5.3
Subjective Assessments
5.3.1 A small range of domestic quality portable AM Medium and Short wave
broadcast receivers encompassing both ferrite rod and whip antennas.
5.3.2 [A prototype or early production Digital Radio Mondiale (DRM) receiver]
5.3.3 A semi-professional HF communications receiver connected to an
external, electrically short, active broadband antenna of the type sold
for general Short Wave reception.
5.3.4 A typical HF Amateur Radio transceiver with a small selection of
amateur band wire dipoles and loaded vertical antennas.
5.3.5 [Any Military and OGD equipment will be provided and operated by the
parties involved]
Source: Radiocommunications Agency RTCG Whyteleafe
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Radiocommunications Agency - VDSL / PLT TWG Meeting - Whyteleafe Surrey - 30 march 2001
Annex A:
DRAFT WORKPLAN for 2nd – 6th April inclusive
(BT and RA personnel)
A1
Day 1:
Loop integrity tests
Carry out Loop specification tests on all 12 circuits and record results. Install and test
VDSL overlay equipment. Repeat Loop tests with VDSL installed and note any
differences.
A2
Day 2:
Antenna Calibration & Measuring System Noise Floor
Compare measuring antennas on far field broadcast signals to verify calibration and
establish any (small) correction factors that may be required. Find a small range of
quiet ‘test’ frequencies spread out within the VDSL frequency spectrum and record
the measuring system and / or ambient noise floor with the antennas well away from
the loops and any obvious noise sources. Repeat with the antennas at 1 metre and
then 3 metres from (coupled into) the Test Loop’s DP cable but with all VDSL
equipment switched off. Establish the lowest measurable noise floor for both
configurations.
A3
Day 3:
Radiated Emission Variations Between Test Loops
Measure the magnetic field for a single VDSL circuit at 1 metre from the “Pole H”
multi-pair DP cable and repeat for each of the 12 identical loops to record variations.
(for each magnetic field measurement, measure and record both differential and
common mode currents)
Select the loop which gave the lowest magnetic field emission (best case) from the
DP cable and deliberately introduce a ‘worst case’ balance fault that will still allow the
VDSL circuit to remain trained up. Measure emissions in this condition and compare
the ‘best case’ to ‘worst case’ spread for this single loop with the ‘best case’ to ‘best
case’ spread for all 12 loops. Repeat (or carry out simultaneously) the same
measurements over the underground section and note any differences.
Assess the information discovered above to determine whether the variations
between emissions from apparently identical loops exceed the calculated value for
the power summation from 12 identical radiators. [10.79 dB]
A4
Day 4:
3 and 10 metre H field measurements
Based on the 1 metre measurement results assess whether the measuring system
sensitivity will permit any 3 metre measurements [ - 9.5 dB] under low emission (nonfault) conditions. If so, make the measurement. If not, introduce a fault to raise
emissions and then make the measurement. Verify whether or not the 1 to 3 metre
regression is about 10 dB. If emission levels and measuring system sensitivity
permit, make a 10 metre measurement and determine the 3 to 10 metre regression.
A5
Day 5:
Wash up meeting (half day on site)
Review the test results and findings. Assess and agree on the feasibility of
determining cumulative effects either through extrapolation of results to date or
further measurements on the “4 acre site”. Agree the structure and substance of the
report to be prepared for the 2nd RA TWG meeting on 30th April and the next CEPT
SE35 meeting scheduled for 9th – 11th May in Paris.
Source: Radiocommunications Agency RTCG Whyteleafe
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Radiocommunications Agency - VDSL / PLT TWG Meeting - Whyteleafe Surrey - 30 march 2001
Annex B:
DRAFT WORKPLAN for 14th – 18th May inclusive
(BT, RA, RSGB; BBC [EBU], [Radio Authority] personnel as appropriate)
Non-Military Spectrum Users
B1
Days 1 & 2 – BT & RA
Practical assessment of Amateur Radio issues in relation to VDSL radiated
emissions and immunity.
(Detailed test procedures to be confirmed in consultation with the RSGB)
B2
Day 3 – BT; RA & RSGB
Demonstration and discussion with RSGB
B3
Day 4 - BT, RA & BBC [Radio Authority]
Subjective tests to assess the effects of VDSL emissions on domestic Medium and
Short Wave AM broadcast reception.
(Detailed test procedures to be confirmed in consultation with BBC and Radio Authority)
B4
Day 5 - BT, RA & BBC [EBU] (half day)
Objective tests to assess the effects of VDSL emissions on DRM reception
(Detailed test procedures to be confirmed in consultation with BBC)
This Annex to be completed before
2nd RA TWG meeting scheduled for
30th April 2001
Source: Radiocommunications Agency RTCG Whyteleafe
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Radiocommunications Agency - VDSL / PLT TWG Meeting - Whyteleafe Surrey - 30 march 2001
Annex C:
DRAFT WORKPLAN for 11th – 15th June inclusive
Military and Other Government Users
C1:
Days 1; 2; 3 as needed - Military and OGD’s
To be worked out with the parties involved and confirmed (subject to requirements for
confidentiality) at the 3rd RA TWG meeting scheduled for May.
C2:
Days 4 & 5 as needed - BT & RA
Repeat tests and unfinished assessments. Test new issues identified during earlier
stages and/or in RA TWG meetings.
This Annex to be completed before
3rd RA TWG meeting scheduled for
May 2001
END
Source: Radiocommunications Agency RTCG Whyteleafe
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