ADSL modem plugged into socket where there's no phone.

[Keith_Beddoe]

I get the impression you worked for OR

@WSH 

Yes I worked for GPO, Post Office Telephones, BT Wholesale and Openreach, nearly 42 years in all.

A lot of time was spend on Private Circuit Repair, and it was standard practice on analogue circuits, to apply "DC Wetting" https://en.wikipedia.org/wiki/Wetting_current

This was to overcome any oxidisation of relay contacts or interception "break jacks" used for testing. Its was only a tiny current of about 5mA which was injected via the line transformer, and was very effective.

Now that we are passing digital signals over copper wires, without any DC component, problems are going to occur, and are not going to be easy to locate.

[WSH]

@Keith_Beddoe.  Again, thanks for that.

I get the impression you worked for OR but I wonder what would be Openreach’s view be of customers injecting voltage to their line?  I would have though it would already be being done if it was going to ward off significant problems?

@HHGTTG.  Oops, sorry I seem to have hijacked your thread a bit here…I’ll clear off now.

@Crimliar.  Again, thanks but I thought that was the same as I said at the start?  I’m a retired IT tech myself so, without wishing to sound arrogant, you can take it the internal wiring is not the issue.

[Keith_Beddoe]

@WSH 

Of course it would affect FTTC in the local serving section.

When I am moved to DV, and I lose the 50V from the exchange, I may inject a small voltage across the line, if I get any issues.

It would be interesting to know on FTTC,  if there is any DC path back through the port in the cabinet, as the injection of a small current through that path, may improve the reliability of the connection.

On ADSL, there may also be a DC path through the MSAN,

[WSH]

Thanks for that @Keith_Beddoe.

That’s an interesting point and would tally with what I’ve seen.

I’m on FTTC.  I’ve just checked and what is going on now is typical of late.  Downstream is operating at 58+ Mb/s (and a throughput test has it downloading at just shy of 55).  58-59 is the “norm” for this line based on many years observations and the same as pre-DV, yet the SH2 says the max attainable is currently 53+ Mb/s with a noise margin of 4.9

It might be just a quirk of the SH2, as I’ve been using my own equipment for several years now, so I’m not familiar with the SH2.  I can’t say I really care so long as it remains stable at 58, I was just curious as to the explanation for the wandering noise margin.

As I say, your explanation tallies with observation so thanks for that.  As an after-thought, would there be any milage in reporting it as a fault?

[Crimliar]

@WSH so in your specific situation:

If the extension you are connecting to is isolated, it can be wired to the xDSL side connectors of the filtered face plate and that will work fine with no additional filtering.  If it's not isolated (not just running to the single socket you have the modem/router plugged into) then it ideally needs to run from the unfiltered connections on either the faceplate or master socket and filtering at the remote socket may be needed.

That you are running over additional cable will put more noise on the line, how significant that is be dependant on the extension wiring!

[Keith_Beddoe]

@WSH 

The line from the ADSL equipment in the exchange will no longer have an voltage on it. This will make it more susceptible to high resistance connections, so that is likely to be reflected, in varying performance.

Just to double check, you are on ADSL and not FTTC?

[WSH]

Just to clarify my own point.

I was running my router plugged into the DSL side of a filtered faceplate.  Since DV I have it plugged into a single socket phone only faceplate.

Performance is the same, but I do notice that the noise margin wanders all over the place more than it used to, hence the speculative question.  Personally, I’m beginning to think it is a problem on the line and just coincidence that it coincides with the switch to DV.

[imjolly]

simple answer if your broadband drops when you make/receive a phone call you need a filter otherwise ok without

[HHGTTG]

Thanks. I have the older wiring without a filtered faceplate/master socket.

[Crimliar]

Without posting reams of info the idea is to have filtering between phone and broadband within your home telephone wiring.

Commonly on older wiring, you'll use a microfilter on every used socket - even if not strictly necessary it'll usually have no significant impact on xDSL speed.  The main exception is that if you have a "filtered faceplate" and are running a modem/router on an extension, then the extension needs to wited to the master socket plate and not the filtered faceplate (or the modem router ends up on the wrong side of the filter).

With the basics in place, you can then "suck it and see"!