Possible to change Target SNR on VDSL?

[#1]

Hi,
We've recently switched to VDSL from a well-performing ADSL connection, and I've unlocked and installed a Huawei HG612 modem to be able to get to some meaningful stats. (I was told the Hub One could be run in Bridged mode, but having since read up on it, I understand that's not actually possible. I use a Mikrotik hAP Lite for PPPoE amongst other things.)
On ADSL our SNR Margin was running around 2.9dB and was stable. (I don't know why it was 2.9dB, I never requested it and we moved in about 2 years ago after buying the house from an old couple - the phone line going into an old Bakelite junction box before winding its way around various high power mains cables and into a crappy 1.5" square socket.)
By my reckoning we should have had an increase of 50% by making the switch to VDSL, but so far we've only seen about a 37% speed increase - and I strongly suspect we could reach the heady heights of 24Mbps (download speed) if we could lower our SNR Margin.
So - can it be done? And can someone do it?
Thanks!
  - Hugh

[#2]

no it can't be done

[#3]

Many thanks for the quick reply Jim
(Meanwhile, the HG612 reports the SNR margin has dropped to ~4.0 dB... Odd!)

[#4]

The dynamic line management (DLM) in your local exchange will alter the SNR setting as it sees fit to keep the line stable
See the following guide for more information
http://community.plus.net/library/browsing/fttc-dlm-what-it-is-how-it-works/

[#5]

Thanks Anoush!

[#6]

Quote from: HughPH

- the phone line going into an old Bakelite junction box before winding its way around various high power mains cables and into a crappy 1.5" square socket.)

This might be part of your problem.  Existing wiring may have been ok for a phone  and passable for adsl but maybe its not up the fttc.
Have you looked inside the bakelite box?  Does it have screw connectors - any signs of corrosion.
Is there only one telephone socket? have you looked inside that? does it have screw connectors.
If you can get inside them can you post  clear pictures of the wiring.

[#7]

What were the estimated FTTC speeds? What speed are you currently getting?
Also, I think the FTTC doesn't directly alter the SNR margin, it adds error protection or caps the speed as it determines is necessary.

[#8]

Guys, many many thanks for trying to help... but I ripped out the old Bakelite box some time ago (it was really nasty inside - very corroded!) and did some "other rewiring" that involved running some CAT5e to a brand new NTE5a. I've even replaced the RJ-11 cable with a home-made RJ-11 to RJ-45 with 2-pair CAT5. (That didn't actually make any difference - but it was worth a go.) Fitting a V3 interstitial plate gave me an extra 1Mbps on ADSL, so I've no doubt it's helping the VDSL too.
Our estimated line speed is 24Mbps, PlusNet's customer portal says it could be between 18.5Mbps and 21Mbps. In fact I've actually unlocked an HG612 router and now have a stable sync at 28,150Kbps (and no CRC errors) thanks to some tinkering and home-grown code - although the customer portal reports 26.5Mbps. At the moment we're enjoying real-world download speeds of approx. 25.5Mbps.
We're about 1 mile from our street cabinet - but I think I can get another 1Mbps on my sync with the current setup.
Before I buy one, do you know if there's ever much mileage in RFI-filtered multiplugs?

[#9]

The answer is no.
Just be wary, using Cat5 to connect from the BT incoming cable to your NTE5a is not only an overkill - it should have been CW1308 - it's not BTOR practice and might attract some comment from an OR engineer should one visit.
Is the BT incoming drop wire twisted pair? CW1411 is the relevant spec. but these days they replace drop-wire with only a single pair cable not two pair. If any part of it is not twisted pair (ie. the old flat figure 8 or "flat" oval cable), that could have an impact.
Ensure you only have a single twisted pair connected throughout. If you have extension sockets and wiring, make sure the bell wire (terminal 3 on the faceplate) is not connected or filtered - which it should be with the vDSL plate - (and the Mk3 has common-mode filtering as well).
If your "data" connection is not at the master and is at an extension, avoid any "star wired" extensions on that wiring - remote testing might identify it as a bridge tap - the typical lengths involved in internal wiring could give issues on FTTC (less common on ADSL).
If you put your phone number into the BT DSL Checker you can compare those figures with your estimate and what you are getting.
Edit: spelling.

[#10]

It may be worth trying a Mk2 face plate. On my long, mostly aluminium, line it give slightly better result than the Mk3, especially noticeable with upstream sync speed.

[#11]

When I tested I found CRC errors slightly less with the Mk3.

[#12]

Many thanks for the information Anotherone!
Everything is twisted pair, even the cable from the NTE5a to the modem.
Only one pair is connected, there are no extensions, the only things directly connected are the modem and a Cisco ATA.
Looks like I might already be running at the limits:

[#13]

Compared to the estimates you are doing well!