Vdsl Rfi Rsgb:ofcom:bt Meeting-june 21 2017

Transcript

EMCC – Impact of VDSL2 on HF Radio governance teamwork values Radio Society of vision Great Britain Advancing amateur radio since 1913 Dr John Rogers, M0JAV Chairman EMC Committee theRSGB @theRSGB Ofcom Conclusions from Investigation into VDSL 1. Noise measurements taken at three sites and at Baldock radio monitoring station were comparable 2. Tests at North London test sites on the bands that the complainants regularly use and where suitable antennas were in use, showed that there were no abnormal levels of electromagnetic disturbance capable of causing harmful interference to radio reception 3. Tests at the third site indicated that the problems were likely to be associated with the extremely close proximity of his antenna to an BT Openreach drop wire theRSGB @theRSGB Conclusions of Ofcom Investigation into VDSL 1. Noise measurements taken at three sites and at Baldock radio monitoring station were comparable • Is Ofcom really saying the background noise levels at Baldock and north London are the same? This is obviously not true - why keep a monitoring station in a semi-remote, rural location if noise levels are no lower than those in London? • You were measuring the instrument noise not the environment • The measurements are the same because the antenna preamp noise on the 30cm loop used means the lowest detectable signal is 32dB(µV/m) this is 40dB (ten thousand times) higher than the true base level at Baldock • This is confirmed by no measurements on the active loop below -120dBm at 100Hz BW - this equates to +34dB(µV/m) in 9kHz theRSGB @theRSGB Minimum signals detectable by antennas 'E' field dB(µV/m) 'H' field dB(µA/m) All RMS in 9kHz BW 40 -11.5 30 -21.5 20 -31.5 10 -41.5 ITU-R P372.13 specifies external noise for Quiet Rural, Rural and Residential environments Results are presented according to CISPR16 methodology Measurements taken at differing BW have been converted to 9kHz to allow comparison Median residential ITU-R P.372-13 Median rural ITU-R P.372-13 0 -51.5 -10 -61.5 -20 -71.5 0.1 1.0 Frequency (MHz) 10.0 Median quiet rural ITU-R P.372-13 30.0 theRSGB @theRSGB Minimum signals detectable by antennas 'E' field dB(µV/m) 'H' field dB(µA/m) All RMS in 9kHz BW 40 -11.5 30 -21.5 20 -31.5 10 -41.5 HLA6120 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 Noise floor HLA6120 0.3 m active loop Median residential ITU-R P.372-13 0 -51.5 Median rural ITU-R P.372-13 Median quiet rural ITU-R P.372-13 -10 -61.5 -20 -71.5 0.1 1.0 Frequency (MHz) 10.0 30.0 theRSGB @theRSGB Minimum signals detectable by antennas 'E' field dB(µV/m) 'H' field dB(µA/m) All RMS in 9kHz BW 40 -11.5 30 -21.5 20 -31.5 10 -41.5 The 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 Noise floor HLA6120 0.3 m active loop Noise floor Welbrook ALA1530 active loop 0 -51.5 Noise floor AY3430 resonant A, B, C loops Median residential ITU-R P.372-13 -10 -61.5 Median rural ITU-R P.372-13 Median quiet rural ITU-R P.372-13 -20 -71.5 0.1 1.0 Frequency (MHz) 10.0 30.0 theRSGB @theRSGB Conclusions of Ofcom Investigation into VDSL 2. Tests at North London test sites on the bands that the complainants regularly use and where suitable antennas were in use, showed that there were no abnormal levels of electromagnetic disturbance capable of causing harmful interference to radio reception • This assertion relies on the mistaken assumption that the noise level observed was similar to that at Baldock whereas the level was 37dB higher • Regular use is not a requirement of the WTA • Many users of the Amateur Service have had to abandon the use of certain HF bands because of the harmful interference from VDSL2 theRSGB @theRSGB Conclusions of Ofcom Investigation into VDSL 3. Tests at the third site indicated that the problems were likely to be associated with the extremely close proximity of his antenna to an BT Openreach drop wire • VDSL levels measured by RSGB and Ofcom are within 5dB of each other when expressed in same units • It is impossible to get >5m away from an overhead dropwire at this 80m by 20m property • The minimum signal at 10.1MHz is obtained with a Wellbrook Active loop antenna directly under one dropwire with its null steered along that dropwire • Nevertheless the VDSL2 levels were so high at this location that they could be measured by the 30cm active loop and Ofcom results confirm that levels are 40dB above the background noise levels at this location (measured using antennas capable of seeing below the necessary 0dB(µV/m)) theRSGB @theRSGB Ofcom measurements of VDSL2 at Shireoaks 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 RSG Measurements Shireoaks using Loop B Loop B can measure down to rural background noise levels of 5dB(µV/m) Results confirm Ofcom measurements of 35 to 40dB(µV/m) Resonant loop means absolute readings only valid at peak. At 3.8MHz reading is 38dB(uV/m) and 5.1MHz 36dB(µV/m) ) Dynamic range reduced by 40dB by Harmful Interference theRSGB @theRSGB Impact of VDSL2 • VDSL2 is present 24 hours a day 7 days a week and is broadband pink noise • For each 10dB increase in this VDSL level above the background noise level 90% of signals present are obscured • So for 20dB rise only 1% of signals present can be received • HOW CAN THAT BE ANYTHING BUT HARMFUL • VDSL2 upstream bands include International Emergency band (3.75 to 3.8MHz) and the low power digital and propagation reporting bands (10.1 to 10.15MHz) theRSGB @theRSGB G3YLA Upstream 2 Downstream 2 / 3 D2D3 by 15dB and 30dB above background in notches theRSGB @theRSGB Revised Conclusions • Background noise could not be measured by test equipment chosen by Ofcom. However the levels of VDSL2 noise were >35dB above that specified in ITU-R P372.13 • Tests at North London location clearly demonstrate VDSL levels which obstruct access to the Amateur Service • Tests at Shireoaks clearly demonstrate there is nowhere to site an antenna to receive signals in the upstream VDSL bands of strength below 35dB(µV/m) so the only way to restore the Amateur Service is to remove the Overhead dropwires or notch the Amateur Bands • Further test sites need to be used to investigate problems with Downstream VDSL2 bands as three sites measured are not representative of all problems reported • Ofcom should withdraw its incorrect statement that no evidence of harmful interference was found theRSGB @theRSGB