VDSL Learning?

Discussion in 'Interference Problems' started by G3RIR, Jan 24, 2019.

  1. G3RIR

    G3RIR New Member

    I have identified an emc problem with my use of BT Broadband and would welcome pointers to understanding what is going on.

    I have an inverted vee on 80m one leg of which goes over the house and is terminated in my front garden. If I transmit 100W CW on 80m the picture on the tv breaks up completely if it is connected to my youview box which is in turn connected to my router. My broadband is BT and speedtests show that I getting 60Mbps download speed.

    If I transmit a test CW message on say 3538 then the tv picture breaks up. If I then pause a short time and resend the test message on the same frequency then the tv picture initially breaks up but then clears. If I pause again and then send the same test message again on the same frequency the tv picture is clear.

    Now if I move frequency to say 3601 and send the same test message then the tv picture breaks up completely. staying on 3601 and sending a second and third test message the tv picture completely clears.

    It is if something is learning about my transmission and somehow stopping the interference.

    I have tried a mountain of ferrite on the incoming broadband cable, on the ethernet out of the router and on the ethernet on the input of the youview box. The ferrite doesn't seem to do anything. My transmitter mains is fed by filters as per GM3SEK. The antenna has a balun at the centre and the coax has lots of ferrite as it leaves the transmitter.

    The broadband into the house comes underground (only about half a metre underground) and is underneath one leg of my 80m inverted vee.

    What is going on? Does ADSL or whatever have some learning capability? Is that in my router or at the exchange or somewhere between?

    I do not know how long I have had this problem. It was only identified a couple of weeks ago when I was operating in AFS on 80m and my XYL (Janette G8TKQ) was wanting to watch Leicester Tigers on BT sports. She reported the break up of the picture. I had a conflict as I would like to have watched the Tigers but AFS came first, just.

    We have had the very high speed BT broadband for about a year but it is very rare that only one of us wants to watch BT sports whilst I am on 80m.

    Neil G3RIR
    Last edited by a moderator: Jan 24, 2019
  2. Ken G3SDW

    Ken G3SDW Moderator

    Think i have spoken to you about this before Neil on the RSGB Tech forum.

    What you must do is to identify were the RF is getting in.

    From memory i seem to remember that you only use your BT YouView box for BT sport so assume that all other viewing is done via Freeview direct off of your TV antenna going into the antenna socket of your TV.

    The RF is no doubt going into either the SMPS to the BT box or via the HDMI cable from the BT box to the TV or into the BT router that the BT box is connected to.

    You say that you have tried a mountain of ferrites on the BT line into your router, any old ferrite will not do, have you used the ferrite recommended by Ian GM3SEK as you mentioned that you have one in the mains feed to your transmitter, doing this will prove or not if it is getting in via the line.

    I have had recently the same problem with this BT YouView box, which by the way is a standard Humax box and that turned out to be getting in via the TV antenna which in his case was connected to the box before it went into the TV antenna socket, a ferrite of the type mentioned by Ian done the trick but again from memory i seem to remember that your antenna goes direct to the TV and not via the BT box.

    It could be the HDMI cable as many of them only use an earth return and not any screening, ie no braid, by obtaining one with good RF screening will prove that or not.

    I have also a Humax box doind similar thins as you without any problems but that does not meant that others do not, what is the BT model number of your box??
  3. Ken G3SDW

    Ken G3SDW Moderator

    By the way Neil you have VDSL not ADSL as your down load speed is as high as you say, learning will not have any bearing to your problem.
  4. G3RIR

    G3RIR New Member

    Thanks for the responses Ken. Yes VDSL not ADSL. I get over 60Mbps. BT upped my speed without extra charge they claim but their billing system is so complex it is difficult to be wure.

    My Youview box is HUMAX DTR-T2100/500G/BT/DF

    My router is BTHub5

    I am intrigued by you saying "learning will not have any bearing ". Where is the learning taking place? In the router, the Youview box or even the TV? Identifying where the learning is taking place will surely identify which device is picking up the interference?

    The problem remains if I disconnect the coax cables from the Youview box which provide the off air tv signal.

    I don't think I have tried ferrite on the 12v lead to the Youview box and I certainly haven't tried ferrite on the hdmi cable.

    You say "The RF is no doubt going into either the SMPS to the BT box or via the HDMI cable from the BT box to the TV or into the BT router that the BT box is connected to." Yes but which one?

    73 Neil G3RIR
  5. Carl G3XGK

    Carl G3XGK New Member

    Hi Neil


    As regards the ‘learning’ by VDSL, yes something like this does happen.

    VDSL allocates a number of bits of data to each 4kHz tone slot in the VDSL frequency spectrum.

    The number of bits each Tone slot can use is a max of 15 bits. It can dynamically allocate the bits to each time slot while in service. If it gets a slot which it receives RFI on, and it is unable to use the slot it will stop use of the slot and distribute the bits (if possible) onto other slots.


    The effect of this is to stop using a slot where there is high RFI on, so the interference will stop causing a problem on that slot and data loss will not occur. This process is being performed by the ‘Green’ Cabinet and Customer VDSL equipment.


    The original plan (ITU-T G993 spec) was to ‘notch’ out or mask the International HF Amateur radio bands, so they would not be used to carry high bit usage, by dropping the TX power level of both the Customer end and Cabinet end transmitters by 20dB in the Amateur radio HF bands. This could still give data coverage, but reduced bit fill in those slots, however, it would also have benefited the receive side for Radio Amateurs as they would probably not be getting wideband noise in return across the Amateur bands.


    GL with resolving the issue.


    Best regards

    73

    Carl G3XGK
  6. G3RIR

    G3RIR New Member

    Carl,

    Thanks for the clarification. You say the "learning" is performed by the "green cabinet" and the customers VDSL equipment. In my case is the customer VDSL equipment the BT Router?

    73 Neil G3RIR
  7. G3RIR

    G3RIR New Member

    admin, can I change the heading from ADSL learning to VDSL learning to avoid confusion? Neil G3RIR
  8. Ken G3SDW

    Ken G3SDW Moderator

    My mistake i can and i have done Neil
  9. Carl G3XGK

    Carl G3XGK New Member

    Hi Neil


    Yes you are correct. The BT Hub 5 has an integrated VDSL modem. Some earlier hubs needed a separate BT Openreach (white box) VDSL modem, but the BT Hub 5 has all the clever VDSL kit built in. The VDSL line I/P is on the back LHS.

    Hpe you successfully resolve the problem, with Ken’s FB assistance.


    Best regards

    73

    Carl G3XGK
  10. Ken G3SDW

    Ken G3SDW Moderator

    As i see it Neil then with a external SMPS it could well be getting into it via the mains input then into the box, or being picked up on the HDMI cable assuming that it is poorly screened and then into the box or into the router via either the mains supply to the router or the phone line to the router.

    You have now confirmed that it is not getting picked up from the TV antenna as you have said it is still there when the TV antenna is disconnected.

    As for learning then that is done via your router and the local cabinet to you and if that was the trouble then when you knock out the TV picture then i would expect your broadband connection to disappear as well, i assume that you have checked this when you are having your problem, but in your favour with underground cables then i doubt very much if it is that.

    By using the ferrite that Ian GM3SEK told you about then use it to prove which route the RF is getting in, you just need to eliminate each one in turn, but dont forget to wind as many turns as possible on the ferrite clamp.

    The other case i had was fortunate to have a family member local to him who had the same box, which made it easy to find were it was getting in, and by the way it was the same model as yours.
  11. G3RIR

    G3RIR New Member

    Ken and others, I have not been able to identify which box or cable is picking up my 80m signal. I could do with some more tips in trying to identify. I tried multiple turns on the ferrite clamps on each cable without success. When the signal to the TV breaks up the broadband itself continues. I have confirmed this by steaming a web cam on my PC. The web cam is public and located on the Norfolk coast 150 miles from here.

    XYL says give up as the only time I have problems is when she trying to watch BT sports when I am not but on the air. It is not my style to give up.

    Neil G3RIR
  12. G3RIR

    G3RIR New Member

    As an aside but maybe related I have connected my RSP1 to my receiving loops and used SDRUNO in an attempt to identify the VDSL characteristics as shown in the RSGB EMC 15 leaflet. I cannot see any gaps in the noise I receive.

    Neil G3RIR
  13. Ken G3SDW

    Ken G3SDW Moderator

    So assuming you are using the clamp on ferrites that Ian GM3SEK recommends then it is fair to say that the line is not picking up RF.

    It cannot be the TV antenna as you have said this is connected direct to the TV and not the Humax box.

    So from that the only other way in is via the mains supply, have you proved this or not??

    It must be getting in somewhere.
  14. G3RIR

    G3RIR New Member

    Ken, a slight correction. The TV antenna is normally connected to the Humax box but disconnecting it makes no difference to the problem.

    I will try again with the ferrite clamps (yes they are the GM3SEK recommended ones ) on the mains to the Router and to the Humax box.

    Neil G3RIR
  15. Ken G3SDW

    Ken G3SDW Moderator

    Mains to the router as well as the line to the router and any cable going to and from the router, as i said must be getting into it in one way or another.

    How low can you go with your TX power before it does not break up?
  16. Ken G3SDW

    Ken G3SDW Moderator

    Neil, thinking about your problem over lunch.

    So what about the make of TV, approximate age, what else is connected to it via cables, have you tried a different TV in its place to see if the problem is till there, just thinking outside the box.
  17. G3RIR

    G3RIR New Member

    Panasonic 32 about 5 years old. I will try a different TV possibly Thursday morning is a useful window.

    Neil G3RIR
  18. Ken G3SDW

    Ken G3SDW Moderator

    How many HDMI inputs has it Neil?
  19. Martin G0HDB

    Martin G0HDB New Member

    Neil:

    Have you tried putting a big #31 ferrite clamp on the HDMI lead that is presumably going between the Humax box and the TV? I've got a similar setup to yours although I can't recall exactly what model my Humax box is, and I found that putting a #31 ferrite clamp on the HDMI lead did make a difference to the overall system's vulnerability to RFI.

    Also, in my experience the BT Home Hubs of all generations are quite prone to dropping the xDSL connection at the slightest provocation - I recently replaced a friend's Home Hub 5 with the combination of a Draytek Vigor 130 VDSL modem and a Billion 7800N router that my friend already owned, and in the ten days since we made the change he hasn't suffered any VDSL dropouts whereas previously with the Home Hub he was suffering a dropout at least daily, and this is on a line that's <200m long between the local cabinet and my friend's house.

    --
    Martin G0HDB
  20. Ken G3SDW

    Ken G3SDW Moderator

    Martin he has not got drop out from his internet signal at all.

    "Ken and others, I have not been able to identify which box or cable is picking up my 80m signal. I could do with some more tips in trying to identify. I tried multiple turns on the ferrite clamps on each cable without success. When the signal to the TV breaks up the broadband itself continues. I have confirmed this by streaming a web cam on my PC"

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