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
