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[mpmc]

Hi folks,

This has been annoying me for some time.

Whenever I plug anything that has power to the line, there is a noticeable buzz, having checked the noise margins on the BT smart hub 2 router, it shows "Noise margin: 5.9 / 8.7", both of these values should be 3.0 or 6.0 IIRC. If I power just the router by a battery backup, without the battery plugged in, these values are 6.0 / 6.0. Plug anything with power from the grid to the line, so just the router and battery backup (powering the router) and those higher values appear.

Having spoken to others (on AAISP's IRC channel), It looks like a ground loop?

So far I've tried 3 different power supplies, the one supplied by BT, a cheap switching power supply from Amazon and a more expensive "UK compliant one".

The one supplied by BT & "UK compliant one" (the more expensive one) are both worse than the cheap switching supply. The noise over the analogue line using an n300 IP is that bad it won't dial out or even hang up!

I remember having this buzz with the Obi110 on the line and sure enough after digging the obi out, the buzz is present however it is only just audible & does not stop phone calls from functioning.

Not using the filter & direct line hook up to the smart hub, nothing else, the noisy margins appear. Power by battery only - once again 6.0 / 6.0!

---

Thankfully this is a backup line in case our Virgin goes down (which it has a few times). Our main voice line is VOIP on AAISP. And as another backup would like to use the OR line as failover. You can never have too many backup options!

If we had a decent mobile signal here that doesn't completely go dead in a power cut I'd use that instead but right now none of the networks appear to work when the power goes.

---

Any advice or suggestions are extremely welcome and valued!

TIA.

[tubaman]

I doubt it's a ground loop as the switching supplies for routers are nearly all two pin devices - ie no earth connection.
There is no way that any device should cause the voice side of your line to be unusable so I'm wondering if you actually have a line fault.

[mpmc]

I doubt it's a ground loop as the switching supplies for routers are nearly all two pin devices - ie no earth connection.
There is no way that any device should cause the voice side of your line to be unusable so I'm wondering if you actually have a line fault.

It's honestly all rather confusing, we had issues with the line before and were told to stop reporting it by OR engineers that came to look, not something they want to/can fix I suppose.

I just can't understand why the noise margins goes up like that, and only on the downstream!

Code: [Select]

Product name,BT Smart Hub 2
Serial number,+0..........................
Firmware version,v0.40.00.04147-BT (Fri Apr 14 12:04:31 2023)
Board version,R01
GUI version,1.79 12_06_2022
DSL uptime,1 days 0 Hours 41 Mins 37 Secs
Data rate,6.0 Mbps / 22.4 Mbps
Maximum Data rate,6.0 Mbps / 24.7 Mbps
Noise margin,6.0/7.4
Line attenuation,13.0/27.7
Signal attenuation,13.0/38.2
VLAN id,101
Upstream error control,Off
Downstream error control,Off
Data sent / received,44.6 MB Uploaded / 191.3 MB Downloaded
Broadband username,bthomehub@btbroadband.com
Public Wi-Fi,Not active
2.4 GHz wireless network name,Wireless 3
2.4 GHz wireless channel,Smart (Channel6)
5 GHz wireless network name,Wireless 3
5 GHz wireless channel,Smart (Channel36)
Wireless Security,WPA2 (Recommanded)
Wireless mode,Mode 1
Firewall,On
MAC address,E4:.........
Software variant,-
Boot loader, 0.1.7-BT (Thu Nov 30 09:45:22 2017)


[Alex Atkin UK]

Is the actual data rate different when the SNR is?

Also makes me wonder if its a problem with the Smart Hub itself, there will be some DC filtering in it that maybe is not working thus why only the battery resolves the problem entirely.

[tubaman]

How are your phone sockets and filters wired as I'm wondering if the bell wire is picking up a lot of noise for some reason?

[mpmc]

We currently do not use the line for phone although that was the plan, may as well wait until we're moved to DV. Which from my testing is crystal clear as expected (I enabled the local line test option hidden on the hub).

At the moment there is no DSL filter at all - well unless a cheap ferrite core on the rj11 counts. Yes, I know it will do very little to help but worth a shot**.

As for how it's wired behind there, sadly I can't get down there to look!  I do know it's connected to the NTE5c MK2. Why the MK4 was swapped out for that I have no idea, ask Kelly Comms 

**: Although I have just noticed in the line stats that the margin is currently lower but that could just be a fluke.

How are your phone sockets and filters wired as I'm wondering if the bell wire is picking up a lot of noise for some reason?

Something I never thought of! You could be on to something, I wonder if there's an easy way to test this? rj11 cable swap maybe? Although I have no idea what cable would have the bell wire omitted.

TIA.

[tubaman]

If yo have extensions wired from the NTE5c then the bell wire is the one on terminal 3 of the removable faceplate. You can just disconnect it and see if it makes a difference.