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Phone Line Noise


Phone Line Noise

Hi all,

I'm wandering whether anyone can help with a phone line noise problem?

I have wanted to upgrade my account recently but have been hampered by line noise that puts the levels just above ( 2 decibels) the requirement for a 1Mb line. It seems I have no hope of getting a 2Mb line then Sad

Following my money being taken, a Whoosh test was performed by BT during the upgrade process. It failed giving a result of 47db where 45db is the threshold. And that was the end of that, no-one wanted to help. The money was refunded and now it seems I'm forgotten about.

(PS - it may be prudent to perform your own whoosh test before starting the upgrade with BT, this would save you the costs of having to process the requests process the money and then refund it all). That said, the money was refunded quickly.


1) Is the line noise constant, or does it fluctuate? i.e. could I take a risk and upgrade the account anyway. From all I have read its pretty doubtful that 2db would make a difference, and bearing in mind that ALL manufacturers put contingency in their quotes I would be happy to go with the risk.

2) Could PlusNet liaise with BT to find out where the line noise is coming into play? They talk to me only up to the point of finding out I don't use them as an ISP, whereas PlusNet have a service contract with them and have more 'weight' to get some answers than I. To date I'm sorry to say PlusNet have simply ried pushing me to BT all the time...almost as if to say "we can't get anymore money from you, so we won't bother helping" <-- a little harsh I know but at least some assistance wouldn't go amiss, afterall I am trying to give you more money.

3) What can I do about reducing line noise, I have heard that the more electrical devices you have attached the more interference will be gained. Would it help by reducing these? What about length of line within the house(i.e. from main outlet to modem, etc.)

4) I have recently obtained confirmation that another ISP can supply a 1Mb line. So why is my line noise too high with PlusNet? This puts me in the difficult position of waying up a move. I have had nothing but good performance and excellent service from PlusNet (to the extent that I log on to the support forums like once every 6 months and wander where some of these problems come from as I don't seem to have experienced anywhere near as many as have been logged!!) so the last thing I want to do is move, however PlusNet are putting me in the position of no choice, I shouldn't have to be limited in my download speed. I don't wish to begrudge PlusNet for a blemish in an otherwise (nearly) spotless record. However my choices currently seem very limited.

So please help in any way you guys can!!!!!!

thanks in advance.


Phone Line Noise

So why is my line noise too high with PlusNet?

Line noise is measured from the BT exchange down BT copper. It doesn't make any difference what ISP you're with, line noise will be the same.

Phone Line Noise

The 47db is the attenuation not line noise. High line noise figures indicate a good line, the figure relates to how much stronger the DSL signal is to the background noise.
You are failing on Loop attenuation. The pass/fail for 1Mb and 2Mb are the same. Attenuation comes about by the distance your line takes to the exchange, the quality of connections between you and the exchange and a variety of other things, including weather conditions.
BT are only obliged to supply a work audio telephone line. You can try complaining to BT phone faults of crackling on the audio phone line or some such similar excuse and get them to come and check your phone line. If the engineer is friendly, he may replace your master socket with a new one or even re-wire from the telegraph pole to the house. This could reduce the attenuation but is no guarantee.

An Important note, even if you manage to fudge a pass at 44.9db and get your 1Mb connection, there is a distinct possibility that you will have lots of drop outs and retransmits that your 1Mb line may not run much faster than 512.

Phone Line Noise

ADSL is known in general as a last-mile Broadband technology. This doesn't relate to "exactly" 1 mile, but rather that it is used in the very last leg of the run.

If it a bit deeper than that, but in essance, it relates to a point between your house and the exchange. It can also be inbetween your house and the exchange, but we won't get too involved there Smiley

As such, only this last-leg needs to fall within the attuation/distance requirments.

The loss is affected by an almost never ending list of issues, but to give you and idea here, I have split them up into two catagories.

Cable joints
Cable guage
Cable type (copper or alluminium)
Cable length
RF filters

Extention quality
Cable type
Cable length
Devices on the line
Sky Box

As you can probably guess, the second list relates to that within your own property.

You only have control over that which is on your part of the property, however, these can often only give little improvment. However, if they are drasticly bad enough, will cause issues.

You can't control and niether can the ISP, the stuff between you and the exchange. Although there is a contract between BT and the ISP, this is between BT Wholsale, and not the main part of BT responsible for the lines.

In adition, the ISP can only enforce line quality, if there contract, or any third-party contract applies. In this case, the third-part contract is BT own contract with the customer.

Unfortunatly, this contract only requires that voice quality is assured. In adition, there rules under which BT must play, also only require them to make sure your line is capable of 33.6Kb connection. AKA dialup.

Not many people are aware of that, and forcing that issue, is somthing I have no experience (for those attempting to get lines fixed).

From what I have read, you have another ISP doing the whole sales pitch thing. In honesty, don't fall for it. By all means move ISP, this isn't about stopping you from moving. What I am saying it look beyond the sales hype.

There are two things I can say about any ISP claiming they can get you 1Mb after talking to them

1: To talk to them, you have walked past there T&C's. These usualy say there advice is not gurenteed and accuracy isn't 100%.

They can and will fall back onto this if you start saying "but you said..."

2: It is the same BT line, the same exchange, the same DSLAM. The same everything in relation to the way your line is tested and provisioned between ISPs.

This means, what you can't get from one, you can't get from another.

This does depend on how your line was tested. If done via woosh, then this is a pretty accurate scale of the line performance. However, does not mean it would fail with BT.

If submitted to BT, they will do a test themselves, and see it is too high. They will also look at the past performance of the line, then pass judgment.

However, in most cases, those about 45dB are rejected. As this is the limit accounting for the added loss from the test itself.

As for improving the loss. There are a few things you can do.

1: Unplug all equipment on the line. Unscrew the master faceplate and insert a phone (corded, not wireless) into the inner socket.

Dial 1 and listen

You should be able to here a slight buzz or hiss. All electrical product do this, though it should never be too loud that you feel the line is not silent.

If it isn;t silent, then you could submit a fault to BT to look at. Do not mention ADSL, as it may only hamper your efforts.

2: Do the same as above, though Plug your ADSL modem in. Now ask for a woosh test, stating you are lookin at the viability and you may have found the problem that caused the previous failure.

If neither of the above two help, there is nothing you can do, but hope BT increase the 1Mb limits at some point.

Phone Line Noise

I think the obvious think is as when people are upgrading is that this is done with equipment connected, and bt will give a 4db margin over the normal 41db noise figure.

But seeing as how you are 2db over this is 50% over the limit, and would require some drastic tweaking, make sure you have a good quality bt approved microfilter, im not sure if the ones that plusnet supply are bt approved or bt "compatible", try with your adsl modem plugged into the master socket with no other extensions, you may also want to look at the quality of the adsl modem itself as some can improve your line gain

Phone Line Noise

Thanks for your efforts guys, much appreciated. I've got a fair bit there to reflect on and I should be able to do some things, and hopefully I can get somewhere with it.

I have to be honest though, I did tell a little white lie when I mentioned the other ISP, BT told me that it could be the line near the ISP that was causing the problem so I needed to get a fix on how you were going to play that one. I wasn't aware that the test was from exchange to house (thanks for that one BT Evil )Probably not particularly fair of me. Please don't be angry!! Cheesy Cheesy

Also, I did have to put in a 60 foot extension line in from my master socket to my study after I moved my study from upstairs to downstairs. I did make it clear to the sparky that it needed to be good wiring but I think he just got a standard extension cable (probably geared for audio calls). Do you think this could have an impact on my attenuation (<-- see, I'm learning!), my 0.5Mb works fine. I guess I could get a wireless router and plug in directly to main socket??

When I last moved house, I moved my number with me, anybody know whether this effects the routing between this house and the exchange??

Clearly I have made a few wrong assumptions, I hadn't had any answers that clear before, so I do apologise. And again, thanks for the assistance.

Finally, is it easy enough for PlusNet to perform the tests (i.e. no costs involved?) as I would like to change a few things round and give the test a few tries?


Community Veteran
Posts: 14,469
Registered: 30-07-2007

Phone Line Noise

Number portability (moving a number to a new exchange) is just a config issue by BT on their switch network. It has no effect on the length of line. It is exactly the same because it is from your local exchange to you, not from your old exchange.

You can ask for a woosh test to be done by PlusNet via contact us - just explain you want to know if 1Meg is possible on your line. However don't push your luck asking for several tests because you want to fiddle at your end. Any woosh test should be done with your router connected to your master socket. This then eliminates any internal wireing issues.

Note: any tests that a BT engineer did would normally have been from the master socket to the exchange (which is all they are responsible for) and not involve your internal wireing or extensions so any fiddling with them is unlikely to make any difference to the DB figures you have been given.

Phone Line Noise

BT will say anything. Min you, quite a few ISPs would say anything just to get a customer.

The idea being that once they have you, you usualy tied to a contractual period.

There are three main sections to the connection

1: Between your ADSL modem to the exchange.

This is the only part that uses the ADSL technology to transfer the data. The rest uses other technologies.

2: The BT ATM Cloud.

This is a mass network spanning the country. All ISP data on IPStream (without confusing you, both PlusNet and BT are IPStream) is intermixed for the most part.

3: The BT Central pipe connection to the ISP

This what interconnects the ISP with the ATM Cloud.

As only section one is ADSL technology, only that part of effected by line loss. You can ignore the othet two (though if there fault was in the Cloud or Central pipe, then it wouldn't just be you affected).

However, it put it in laymans terms. You can unteather the pigs, because there aint flying nowhere.

Onto your cabling. A sparks idea of quality cabling is alarm cable. It is a lot more common than CAT5 or true telephony cable.

60 foot is also a very long way. Did it have to be that far?

That is one possible factor imparing the result (between the quality and length of the cable).

As for charges for tests. You need to keep these requests to a minmum. ISPs are not charged for them, but they are a manual process. Somthing they don't have all that much time for.

To save time however, what connection ahrdware are you using?

If you have a router, or some certain types of USB and PCI modem, you can usualy get the attuation and SNR values without having to contact your ISP at all.

There is a larger error factor in the results from this, but it is enough to test various setup changes you have made.

Phone Line Noise

thanks for the prompt response yet again (you guys are pretty on the ball aren't you).

Did have to be 60 foot unfortunately. Moved my entire study (custom units and all) and converted half my garage. It was easier to go from socket into loft across the house and down a wall to get to the new study than to take from another point from the house.

Happy to get new cabling if your could give me a steer on what to get (true telephony better than cat5?)

I have a Fujitsu USB modem connecting at 576/288. Never given me any problems but I can't really vouch for its quality. About 18 months old now I think (and yes I've been with PlusNet all that time).

I have hunted high and low on the net for the commands to use to get the info. from the modem but can't find anywhere. What thresholds do I need to look out for with the Signal to Noise Ratio?

Don't worry, I'll keep ay requests to a minimum. I have even looked for utilities on the net that may replicate the Whoosh test ot other tests but can't find a thing. Could be a problem with not really knowing what to look for though. This would be good as I could do the varous changes and contact yourselves only when I had seen an improvement from an initial baseline.

Phone Line Noise

Local woosh tests are dependant on the modem drivers and/or modem/router firmware.

Other than the software thats comes with modems, there is not other method of getting the information.

ISPs get the data from a set of BT provided tools. Only your current ISP can get the details of woosh tests. No ISP can get the details if you are not on ADSL.

BT will have to do nothing but take you word for the woosh results, even if there sales team have the knowledge to interpret them right (doubtful, such a large company use backwards facing drones).

In honesty, between telephone cable and CAT5, you can't go wrong. The real benefit will be from a solid core type (not stranded).

Some telephony cables say they are very good quality, but there not. CAT5 is a standard in signal loss requirments, so there is little in the way that can go wrong in your selection of that.

CAT5 is thicker though, so that may be an issue, though not too much of a big one.

I will look into the modem, to see if it does provide fht einformation you need. Saving on the time you need to contact support.

Phone Line Noise

You can read through this in the tutorial section.

Fujitsu modem is pretty good, I started off with that one. Never hiccuped once.

SNR figures will give problems when they start to fall below 15db, at single figures you can almost forget it.