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Wednesday, November 29, 2017

An interesting discussion about VDSL Emission Investigation...

Hi all,

an interesting discussion about the VDSL Emission Investigation thru the bands is continuing over here:


An initial letter from Robin, G3JWI (Nov 2014) as follows...

"The EMC Committee is carrying out an investigation of the significance of interference to amateur radio from leakage from VDSL systems. The emissions from VDSL are continuous and indistinguishable from white noise and may go unnoticed.

VDSL2 covers frequencies up 17.66MHz. The downstream and upstream bands alternate and the easiest way to detect VDSL is to look for the change in noise level at the band transitions. These are nominally 0.138MHz, 3.75MHz, 5.2 MHz, 8.5 MHz, 12MHz, and 17.66MHz. The band that predominates depends on distance of the house from the street cabinet. Most problems are seen when the connection to houses in the area is by overhead cables.

The effect will be that received signals seem weak and the background S meter reading higher than expected. To check for VDSL emissions tune about 75kHz either side of the nominal transition frequencies. Ignore off air signals and local incidental noise. Tuning around these frequencies and listening while watching the S meter will show a noise step if there is VDSL interference. If an SDR is available the step will be clearly seen and the 4.3125kHz patterning of the VDSL signal may be visible on a waterfall display, but careful adjustment of the contrast may be required for this.

If you want to see some examples look at the 2014 RSGB Convention paper

There is also an item on VDSL emissions in in EMC Matters in RadCom December 2013.

The key facts we would like you to report are the frequencies and size of the steps. If you have an SDR, spectral and waterfall plots would be very useful. If you are not QTHR please give some indication of your location.

Please reply via this forum, to
emc.chairman@rsgb.org.uk or to myself directly.
Thanks and 73
Robin G3JWI
Acting Secretary EMCC

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