VDSL2 interference what options have I got
Im located in a urban location with overhead telephone cables with VDLS2 Fiber to the node running ITU G.993.2 profile 17A, wide band noise is at least 20dB above natural floor , reception below 500kHz at nite when RFI is very low I have received NDB 100 watt 2500kms 9-5 receptionm, antenna is a E feild Mini-Whip up 12 mts with 13 mrt RG11 quad sheild coax ground end connected to 1.5m earth rod, Kiwi SDR 20cm from earth rod , ethernet isolator common mode filter, power fed via double insulated linear 8 volt power supply (8 volt mini-whip power feed) 3 amp 5 volt linear regulator power to Kiwi SDR , im assuming have little common mode RFI from my cabling.
The VDSL2 up and down stream bands are very evedent from the waterfall display even the VDSL2 guardband gaps is clearly visible
Any Ideas or suggestion or just install it at a remote location away from VDSL2.
Comments
There was a discussion about this recently over on the wsprdaemon forum: groups.io/g/wsprdaemon/topic/vlsl_telecom_network/112581272?dir=asc
I've told this story before but will repeat it in case anyone has self-interference problems.
Before my apartment building was wired for fiber (FTTP) all we had was VDSL2 from a pedestal on the street over the crappy building CAT3 telephone cable. I had some noise, even after adding some toroids, around -95 to -100 dBm (uncalibrated) as shown in the first image. Not too bad.
One day one of the VDSL band segments jumped up almost 15 dB in signal strength. I looked at the VDSL statistics page on the modem and the "downstream" transmit power from the line card in the pedestal was at +14 dBm compared to the usual +3 dBm, which is what the statistics page said my modem was transmitting in the "upstream" direction. They were always about equal in the past.
After resetting the modem there was of course a VDSL retrain cycle and the downstream power dropped again to +3 dBm. I happened to catch this on the waterfall in the last image. Not quite as good as what I had before. But a big improvement.
I might hook up 5 port switch a battery use laptop and turn off power to the house, how much is from my telephone cabling inside my property, also read a guy in the UK used a current probe and QRM reducer to null out his VDSL2 QRM, early days yet will update my results
To be honest, if you live in an urban area, and have the ability to do so, then the best results will be obtained by moving the KiWi to an electrically quiet location.
The ITU noise curves, and my own experience, indicate that you will obtain 10 to 20dB reduction in noise floor by doing this.
If you can't do that, then try a balanced antenna, rather than using an unbalanced High Impedance E-Probe. At my home location, where the antennas are surrounded by overhead phone lines and power cables, I find that either a broadband loop or old Datong AD370 active dipole tend to work the best, and their polar pattern helps to null out the noise from the worst direction.
Try the different antennas for yourself
g8jnj.zapto.org:8073/?ext=ant
If that doesn't work, then try to locate the noise source. I use a TinySA Ultra hand held spectrum analyser (which has a built in pre-amp) and short whip antenna. This makes it very easy, and inconspicuous, to walk around the local area "sniffing" near the telephone poles and drop wires.
It is very often one poor set of self installed phone sockets and extension cables that cause the line to be unbalanced and radiate. Depending on your relationship with your neighbours, it may sometimes be possible to help them resolve the issue, and improve their internet speed and reliability in the process too. Fibre is now becoming the standard method of delivering broadband internet in the UK, so this problem may eventually go away, but unfortunately the switched mode power supplies provided with the router and ONT still tend to be noisy.
Regards,
Martin
A remote location is always good for an antenna ;) Particularly for E-field.
Depending on where you live, you might also report the issue to the telecom regulation authority.
Our authority (OFCOM) has ordered the telecommunications service to renew all lines in the area and notch the amateur radio frequencies.
But VDSL seems to be only part of your problem, there is also a lot of other noise.
As Martin has suggested, much of the coupling to an HF antenna system from VDSL, BPL or DOCSIS uplink tends to be by way of common mode injected current rather than radiated, either near-field or far-field, means.
Achieving high symmetry with attendant high common mode rejection of the rx system can help a great deal, particularly at long wavelength where actual radiation falls off due to minuscule radiation resistance of the conductors involved. This makes complete symmetric and balanced receive systems, rather than single ended ones such as monopoles, a far better choice.
This doesn't get rid of all coupling mechanisms, but it can greatly help. Getting rid of CM was one of the prime reasons for going to the balanced configuration in the SAS.
If you don't live in the US, you may still be able to order this HW at a reasonable price, even with local VAT included.
Glenn n6gn
Away from VDSL2 noise spectrum picking up VLF NWC 20dB above the noise and very clean eye diagram, interesting monitoting FT8 on 18104 above VDSL2 noise much better than FT8 on 14.074 s/n figures are better on 18Mhz, its seems to me I got a 20dB noise penailty between 2 to 17 Mhz
If you use a broadband display, particularly one with min/max hold you can appreciate where the QRM is by the ham-band notch depths as well as how much it is hurting your SNR.
Here is capture of reverse channel, user ==> Internet, Internet-over-coax, QRM leaking from a neighbor of N6GN received on an RX888 and recorded with ka9q-web from ka9q-radio. Some of the ham band notches are IDed. The depth of the notch indicates how badly the SNR is being hurt by this interference.
This is being received by a 6m dipole SAS which has quite flat field response over these marked frequency range.
Because of the notches, ham band performance isn't being hurt but SWL and other listening at other frequency certainly is.