theRSGB @theRSGB

vision valuesgovernance teamwork

EMCC– ImpactofVDSL2onHFRadio

of Great Britain

Advancing amateur radio since 1913

Radio Society

Dr John Rogers, M0JAV Chairman EMC Committee

theRSGB @theRSGB

OfcomConclusionsfromInvestigationintoVDSL1. Noisemeasurementstakenatthreesitesandat

Baldock radiomonitoringstationwerecomparable2. TestsatNorthLondontestsitesonthebandsthat

thecomplainantsregularlyuseandwheresuitableantennaswereinuse,showedthattherewerenoabnormallevelsofelectromagneticdisturbancecapableofcausingharmfulinterferencetoradioreception

3. TestsatthethirdsiteindicatedthattheproblemswerelikelytobeassociatedwiththeextremelycloseproximityofhisantennatoanBTOpenreach dropwire

theRSGB @theRSGB

ConclusionsofOfcomInvestigationintoVDSL1. NoisemeasurementstakenatthreesitesandatBaldock radio

monitoringstationwerecomparable• IsOfcom reallysayingthebackgroundnoiselevelsatBaldock and

northLondonarethesame?Thisisobviouslynottrue- whykeepamonitoringstation inasemi-remote,rurallocationifnoiselevelsarenolowerthanthoseinLondon?

• Youweremeasuringtheinstrumentnoisenottheenvironment• Themeasurementsarethesamebecausetheantennapreampnoiseonthe30cmloopusedmeansthelowestdetectablesignalis32dB(µV/m)thisis40dB(tenthousandtimes)higherthanthetruebaselevelatBaldock

• Thisisconfirmedbynomeasurementsontheactiveloopbelow-120dBmat100HzBW- thisequatesto+34dB(µV/m)in9kHz

theRSGB @theRSGB

Minimumsignalsdetectablebyantennas

ITU-R P372.13 specifies external noise for Quiet Rural, Rural and Residential environments

Results are presented according to CISPR16 methodologyMeasurements taken at differing BW have been converted to 9kHz to allow comparison

-71.5

-61.5

-51.5

-41.5

-31.5

-21.5

-11.5

-20

-10

0

10

20

30

40

0.1 1.0 10.0

'H' field dB(µA/m)

'E' field dB(µV/m)

Frequency (MHz)

All RMS in 9kHz BW

Median residential ITU-R P.372-13

Median rural ITU-R P.372-13

Median quiet rural ITU-R P.372-13

30.0

theRSGB @theRSGB

MinimumsignalsdetectablebyantennasHLA6120 0.3m loop was designed to measure HF common mode currents at distances up to 0.5m from conductor (AY3920)The antenna preamplifier noise prevents field strength measurements below 32dBµV/m

-71.5

-61.5

-51.5

-41.5

-31.5

-21.5

-11.5

-20

-10

0

10

20

30

40

0.1 1.0 10.0

'H' field dB(µA/m)

'E' field dB(µV/m)

Frequency (MHz)

All RMS in 9kHz BW

Noise floor HLA6120 0.3 m active loop

Median residential ITU-R P.372-13

Median rural ITU-R P.372-13

Median quiet rural ITU-R P.372-13

30.0

theRSGB @theRSGB

MinimumsignalsdetectablebyantennasThe unshielded AY3430 resonant loops A, B, C were designed to measure down to 0dBµV/m and the Welbrook loop ALA1530 can measure to below rural background levels these are 30dB better than the 0.3m active loop

-71.5

-61.5

-51.5

-41.5

-31.5

-21.5

-11.5

-20

-10

0

10

20

30

40

0.1 1.0 10.0

'H' field dB(µA/m)

'E' field dB(µV/m)

Frequency (MHz)

All RMS in 9kHz BW

Noise floor HLA6120 0.3 m active loop

Noise floor Welbrook ALA1530 active loop

Noise floor AY3430 resonant A, B, C loops

Median residential ITU-R P.372-13

Median rural ITU-R P.372-13

Median quiet rural ITU-R P.372-13

30.0

theRSGB @theRSGB

ConclusionsofOfcomInvestigationintoVDSL2. TestsatNorthLondontestsitesonthebandsthatthe

complainantsregularlyuseandwheresuitableantennaswereinuse,showedthattherewerenoabnormallevelsofelectromagneticdisturbancecapableofcausingharmfulinterferencetoradioreception

• ThisassertionreliesonthemistakenassumptionthatthenoiselevelobservedwassimilartothatatBaldock whereasthelevelwas37dBhigher

• RegularuseisnotarequirementoftheWTA• ManyusersoftheAmateurService havehadtoabandontheuseofcertainHFbandsbecause oftheharmfulinterferencefromVDSL2

theRSGB @theRSGB

ConclusionsofOfcomInvestigationintoVDSL3. Testsatthethirdsiteindicatedthattheproblemswere

likelytobeassociatedwiththeextremelycloseproximityofhisantennatoanBTOpenreach dropwire

• VDSLlevelsmeasuredbyRSGBandOfcomarewithin5dBofeachotherwhenexpressedinsameunits

• Itisimpossibletoget>5mawayfromanoverheaddropwireatthis80mby20mproperty

• Theminimumsignalat10.1MHzisobtainedwithaWellbrook Activeloopantennadirectlyunderonedropwirewithitsnullsteeredalongthatdropwire

• NeverthelesstheVDSL2levelsweresohighatthislocationthattheycouldbemeasuredbythe30cmactiveloopandOfcomresultsconfirmthatlevelsare40dBabovethebackgroundnoiselevelsatthislocation(measuredusingantennascapableofseeingbelowthenecessary0dB(µV/m))

theRSGB @theRSGB

OfcommeasurementsofVDSL2atShireoaks

Strongest amateur service signal Seen 53.5dB(µV/m)

Strongest commercial HF seen 64.4dB(µV/m)

Conclusion VDSL2 is obscuring 40dB of the 65dB dynamic range. This is Extremely Harmful Interference.

theRSGB @theRSGB

RSGMeasurementsShireoaksusingLoopBLoop B can measure down to rural background noise levels of -5dB(µV/m)

Results confirm Ofcommeasurements of 35 to 40dB(µV/m)

Dynamic range reduced by 40dB by Harmful Interference

Resonant loop means absolute readings only valid at peak. At 3.8MHz reading is 38dB(uV/m) and 5.1MHz 36dB(µV/m) )

theRSGB @theRSGB

ImpactofVDSL2• VDSL2ispresent24hoursaday7daysaweekandisbroadbandpinknoise

• Foreach10dBincreaseinthisVDSLlevelabovethebackgroundnoiselevel90%ofsignalspresentareobscured

• Sofor20dBriseonly1%ofsignalspresentcanbereceived

• HOWCANTHATBEANYTHINGBUTHARMFUL• VDSL2upstreambandsincludeInternationalEmergencyband(3.75to3.8MHz)andthelowpowerdigitalandpropagationreportingbands(10.1to10.15MHz)

theRSGB @theRSGB

G3YLAUpstream2Downstream2/3D2<U2>D3 by 15dB and 30dB above background in notches

theRSGB @theRSGB

RevisedConclusions• BackgroundnoisecouldnotbemeasuredbytestequipmentchosenbyOfcom.HoweverthelevelsofVDSL2noisewere>35dBabovethatspecifiedinITU-RP372.13

• TestsatNorthLondonlocationclearlydemonstrateVDSLlevelswhichobstructaccesstotheAmateurService

• TestsatShireoaksclearlydemonstratethereisnowheretositeanantennatoreceivesignalsintheupstreamVDSLbandsofstrengthbelow35dB(µV/m)sotheonlywaytorestoretheAmateurServiceistoremovetheOverheaddropwires ornotchtheAmateurBands

• FurthertestsitesneedtobeusedtoinvestigateproblemswithDownstreamVDSL2bandsasthreesitesmeasuredarenotrepresentativeofallproblemsreported

• Ofcomshouldwithdrawitsincorrectstatementthatnoevidenceofharmfulinterferencewasfound