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[navzptc]

I had FTTC fitted (80/20) just under one month ago and as a Radio Amateur transmit mainly on the 7 & 14 MHz bands, but can at times use all bands up to 50Mhz.

I have been looking on the web to ascertain whether it is recommended to power down the VDSL whilst transmitting, but can't seem to find a definitive answer. Some sites say that the VDSL should not be affected by the transmissions as the amateur bands are omitted from the frequency range used  for VDSL, whilst others say there will be problems.

I presently power down the router followed by the modem when I intend to transmit and vica versa when completed, but this is getting to be a bit of a pain - Will my line stats suffer due to this over time?

Any recommendations / advice on how to best handle this situation is much appreciated in order to find the best way forward.

Regards,

Andy

[burakkucat]

Hello Andy and welcome to the Kitz forum.

You ask an interesting question. The current VDSL2 plan uses frequencies up to 30 MHz. I tried, with a quick Google search, to find the frequencies of all the authorised UK amateur radio bands up to 30 MHz and got rather confused. (There seem to be newer LF bands . . . I have vague memories of 160m, 80m, 40m, 20m & 10m.) Even the RSGB's website was not too helpful to me.

Perhaps you could list the frequency ranges in which you transmit, please? Then with sight of those frequencies, one of our wizards may be able to comment. Here, of course, I am thinking of Asbokid.

The regular power down / power up sequences of the modem will undoubtedly be 'frowned upon' by the DLM and you may find yourself put onto a banded profile, with synchronisation limited to a lower rate.

The alternative question is just how much are your transmissions affecting the VDSL2 circuit? Do you have any statistics to show a detrimental effect?

[navzptc]

Hello Andy and welcome to the Kitz forum.

Perhaps you could list the frequency ranges in which you transmit, please? Then with sight of those frequencies, one of our wizards may be able to comment. Here, of course, I am thinking of Asbokid.

The alternative question is just how much are your transmissions affecting the VDSL2 circuit? Do you have any statistics to show a detrimental effect?

Many thanks for your response burakkucat, and following is the information you asked for:

Frequency ranges used (Mhz): 3.5-3.8, 7-7.2, 10.1-10.15, 14-14.35, 18.068-18.168, 21-21.45, 28-29.7, 50-52.

To be truthful, I have not transmitted without switching all the gear off first, as I want to try and maintain my profile (77.4/20) and didn't want to induce any problems by my transmissions.

I have not got round to modding the spare ECI modem (r) yet to see the stats on the line.

As you say, hopefully one of the forum wizards will be able to assist 

[JGO]

If there is enough coupling ANY frequency can cause trouble - here at one time we got a buzz every 7 sec on the radio as a 200 MHz radar a mile or two away rotated. This is a non-linearity effect so reducing the coupling is very effective at 2 or 3 dB reduction in effect per dB of pickup.  TV sets can be succeptible due to the TV coax feeder acting as a Marconi aerial - same effect. The first line of attack is to try and reduce the coupling  by spacing and aligning aerial and VDSL cable at RT angles.
Also, it should be possible to use something like the (FX1588 ?) ferrite rings round TV coax for same frequency interference to to impove the twisted pair's even mode rejection. NB the rejection is sensitive to the position of the ferrite along the cable.  (Of course the best solution would be fibre all the way and don't mess about ! )

About switching off the modem, AIUI if it has the "Last Gasp" facility the effect on synch rate is supposed to be reduced, but the thermal shock effect is still there. I suspect the "switch on surge" is a bit of an urban myth, no valve heaters or chokes in the PSUs at the present time !
   

[asbokid]

Hello navzptc!  Welcome to the forum. 

It doesn't really address the issue, but this article on ham radio and DSL filtering might interest you:

http://forum.kitz.co.uk/index.php/topic,11277.msg237197.html#msg237197

You're stuck with a Hobson's Choice 

Leave the CPE modem powered up and risk inducing line noise from keying up. That noise could eventually cause DLM to impose lower sync speeds. Or else power down the CPE and risk DLM seeing that as line instability!

Perhaps the best solution would be to check whether the ham kit is actually inducing line noise.   That could be achieved by taking a QLN (Quiet Line Noise) snapshot with the ham kit off, and then resync the modem while the radio is keyed up. Repeat for all amateur radio bands that you transmit in.  And then calculate the difference of those QLN snapshots. Perhaps the easiest way to see if there's a problem would be to plot the QLN graphs and make an animated GIF from them.

cheers, a

P.S. There's a lengthy article on ham radio interference to/from DSL knocking about somewhere. When it turns up I'll link it from this post.

EDIT: The info contained in it is probably old hat to you, but here it is any way:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.192.3155&rep=rep1&type=pdf

[Chrysalis]

my thoughts are if it can affect your dsl then it probably affect neighbours also.

have you ever checked with neghbours if they ok with you transmitting?

[JGO]

my thoughts are if it can affect your dsl then it probably affect neighbours also.

have you ever checked with neghbours if they ok with you transmitting?


NEVER,NEVER do this !  someone will invent something, say the toaster doesn't get hot enough !   It is powerful evidence if you can demonstrate that you have no problems at home, but people will believe  things without any evidence -  someone recently was persecuted out of his house  because the locals didn't know the difference between paediatrician and paedophile !

[navzptc]

A very big thank you to all those who have responded to my question 

In answer to one question, when I was running with ADSL2, I did not have any problems, or suffer with TVI even though I used to run a pre-amp in the loft - In fact I used to get interference from a neighbours telly until they changed it!

I think asbokid has come up with the answer with what to try next, so it looks like I will be tweaking my spare modem in the near future to try and obtain some real time stats - Its just the increased frequencies that are used with VDSL that got my mind thinking.

Will let you know when I have managed to achieve some figures 

[guest]

Well I guess it'd depend on what tones aren't in use on VDSL2 and do they correlate with ham radio? My guess would be that they don't.

I'm sure someone here has details of tones currently in use on VDSL2?

@Chrysalis : the OP at least has a licence to transmit on those frequencies, unlike the BT users who got supplied "Homeplugs" by BT and transmit 24/7/365 for example.

* rizla once held a MRGC when morse @ 30wpm was required; dates me a bit now

[burakkucat]

my thoughts are if it can affect your dsl then it probably affect neighbours also.

That may well be the case but transmitting on those frequency bands is permitted by the licence held. The actual problem is with the xDSL technology in assuming that it has a right to radio spectrum silence -- which it most definitely does not possess! 

Edit: I see rizla got to the point before me. 

[guest]

I think we sort of overlapped

I can of course understand Chrysalis point of view but the basic issue here isn't the frequencies in use, it is the delivery mechanism - ie unshielded twisted pair.

That's the basic problem and one which we're stuck with now for probably 15 years outside major conurbations. Its only going to get worse and (don't laugh) but I'm starting to wonder whether houses with overhead phoneline connections are going to start to lose value due to lower speeds. We'll see....

[Chrysalis]

are underground BT cables resistent to radio?

When I got adsl I had an attentuation of 49-50db. synced at around 6000kbit or so maybe bit higher.
Friend of mine had just got adsl also, my coincidence he had also 50db attenuation.

We both had speedtouch modems and had the famous DMT tool (some may remember it).

Now if we compared our bitloading and snr graphs at say midday, they both looked the same (assuming I wasnt getting one of my daytime noise bursts).  They had same sort of dropoffs and looked almost mirror.  However there was differences in how the lines ran.  At night his snrm barely changed, he maybe lost 0.5db or so at the most.  Whilst on my line all the higher tones got destroyed, btswapping turned them off and my snrm was trashed.  In short he could maintain a daytime sync at night, I couldnt.  The other change was I would see lots of variance on the bitloading and snr, as was lots of interference on the line, evident 24/7.  I had huge amounts of crc errors he didnt.  His line was on a business park and underground all the way, me in a havily built up residential area near city centre and line fed from pole.  Although underground up to the pole.

At night I used to hear a radio station (foreign) transmitted through my pc speakers.  I never hear it anymore.

[waltergmw]

@ Chrysalis,

I recall the esteemed Ezzer telling us that he had experienced some quite nasty RFI on underground cables, but in general it seems that overhead lines are far more likely to be affected.

Kind regards,
Walter

[guest]

are underground BT cables resistent to radio?

No, however depending on what is on top of them and the frequencies involved they do attenuate induced RF to a certain degree.

[NewtronStar]

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