Noisy Phone Line

[Boa]

The other day my phone line suddenly got noisy, this noise (which is like a hissing/sea noise with fax like beeps occasionally) got quiet bad, to such an extent that a conversation was not possible, at other times it is quiet passable but can still be heard. During all this the ADSL dropped only once but otherwise worked fine, this was over three to four days.
I called Telkom and the techie checked the line, the ADSL signal and tried another pots filter, these were fine with no problems, then he suggested it could be the modem/router (Microcom AD 2656), so we switched this off and the noise on the phone disappeared. He suggested I go and get a new modem/router which I installed and got working fine, but the noise on the phone has not gone away and is still there as before, so I am left wondering what the cause of this noise could be and having to call Telkom back to check again and fighting to get my R140 call out charge returned.

 

[antowan]

My extra line had this problem this past week. They needed to replace the copper to fix it. Parts of Telkom's network is pretty old. I suspect this will happen often from now on...

 

[Surv0]

Cant believe the stupid ass technician told you it was your router, hes an idiot. Obviously the router makes a noise on the line otherwise it wont work. Thats what those pots filters are for, to seperate the analogue voice signal noise and the data signal noise, so you should just hear the voice and not data. If you changed the filter and it helped, then your filter is at fault. If it didnt make a diff and you still hear the noise then its more than likely a problem on the line. Those support agents have no physical way of testing for noise on their side and can only rely on your judgement and troubleshooting. If all else fails they have to log a fault to get a technician to check on it. Half the time those agents tell u to swap the modem, they dont really know wat they are talking about..,.

 

[Boa]

Thanks Surv0
I thought as much, it was the techie who came to my office who told me all of this. And when he started telling me it was my florecent ceiling lights that could be the problem you start to wonder, as this was all here before I installed the adsl and it worked without any problems in the interim.

 

[Surv0]

lol, blaming the ceiling light, thats funny, must be really struggling for ideas. In most cases those techies than get sent out dont know any more than the techies on the other end of the line.

 

[Major Boredom]

They need to go read " The bastard Operator From Hell"

 

[Freak_c]

I have a different situation! I have ADSL at home and told them to install it at two places (1 in the lounge for phone there, and the other in the study with computer and another phone). Anyway each box that is on the wall has 2 ports/jacks for the phone or whatever to be connected. I think its a splitter so you can have fax/adsl/and phone in one.

Now the filter is for the adsl and phone right, to clear the noise?

I have the router connected directly to the wall and my phone also direcctly to the wall but it's in the port above. only sometimes do i get crackerling on the line.

Do i really need to have the filter on??

 

[Surv0]

Without that filter you are going to hear alot of noise caused by your router, only if your router is online and operating. If the router is off u dont need the filter...

 

[damian24]

Obviously the router makes a noise on the line otherwise it wont work.

Iiiish, technie not that stoopid... ADSL should NOT make a single sound in the voice part of the band as it's using somewhat higher frequencies.

The primary purpose of the pots filter is to impedance match your phone to your line... why, otherwise you ADSL connection would drop everytime you picked up the phone.

so in essence, the pots filter keeps you ADSL connection stable if you have a phone connected, otherwise it's just a piece of useless hardware helping to increase your snr and attenuation on the line.

EDIT as for the flourencent claim, there's plenty to it when the ADSL lines are running near them, however this has more of an effect on the DSL portion due to the radio noise it generates.

Hearing noise on your phone line from ADSL when your phone has a bandiwdth cap of barely 3400Hz and ADSL operates well above hearing range at 25Khz... there is of course one expection to this, as always, if you have a crappy 50 buck jobbie, then it's possibly demodulating the ADSL signals in the 25kHz range and if may be the phone and not the modem but that's only if the pots filter is giving grief.

I really wonder about some of the comments I see on this board sometimes <now awaiting flaming!>.

D

 

[3Y3W17N355]

Flaming has begun.

I tried without my pots filter, adsl still worked in the call, but there was noise, so>

 

[damian24]

well yourself, I suppose it probably won't turf every connection.

(1)some phones do demodulate the ADSL portion and cause noise, I haven't seen a siemens do it though... yet, but who has 400 bucks to spend on a siemens analogue phone?

(2)if your modem is making a noise on the analogue portion when it's running and you've replaced the filter, it's your modem thats up to crap... caveat, since ADSL is at the exchange as well it's possible for the DSLAM to introduce the same noise but very unlikely as there is a high pass filter and surge protector on the DSLAM and another lowpass filter on the POTS.

(3)to see the effects that having no filter on the line, you'd need to monitor the live snr and attenuation signals, most ADSL modems will retrain as the changes that the phone introduces to impedance when picked up/put down or being hooked up to the line without a filter will force a retrain and get the DSLAM to raise the output level a couple of db to maintain the connection.

D

 

[Surv0]

The primary purpose of the pots filter is to impedance match your phone to your line... why, otherwise you ADSL connection would drop everytime you picked up the phone.

This is not true, the primary function of the pots filter is to seperate the analogue signal from the data signal. Without that filter you will be hearing both frequencies, the voice as well as a buzzing, humming sound which is created by the router and is completely normal. The filter is not there to stop the line disconnecting if you use the phone, you can test this by just removing the filter and trying the phone, you will find it wont disconnect your DSL. If it does then the problem isnt lying with the filter but with the wall jack/splitter.

 

[damian24]

@Surv0,

I guess you're right, perhaps you should take a read of ETSI TS 101 952-1-4
though, I reiterate, any decently built phone won't exhibit any interference with ADSL, ADSL is waaaay above normal hearing range.

The reason you could hear noise on a phone without a pots filter is because badly designed circuitry is effectively demodulating the ADSL signal, any decent phone design would already have a low pass filter integrated and thus not exhibit your 'buzzing', failure to have a filter though causes very definite issues when picking up and puting down you phone, audio techies know this only too well how impedance changes when adding and removing devices in parallel.

from ETSI...
The main purpose of the ADSL over"ISDN or POTS" universal splitter is to separate the transmission of either
baseband POTS or ISDN signals and broadband ADSL signals, enabling the simultaneous transmission of the two
services on the same twisted pair. The splitter also serves to protect POTS or ISDN from interference due to egress (and
ingress) from ADSL signals. Equally it protects the ADSL transmission from ISDN intereference, and transients
generated primarily during POTS signalling (dialling, ringing, ring trip, etc.). It must also prevent interference to the
ADSL service due to fluctuations in impedance and linearity that occur when POTS telephones change operational state(e.g. from off-hook to on-hook)

D

 

[Surv0]

Yup i cant dissagree with you on that...all depends on how deep you want to look into it :>

 

[Boa]

The posts have been interesting, but reiterating what I said in the first post, the Telkom guy tried a brand new filter and the noise was still the same. Also while we are waiting in the queue for the tech guys next visit (3 days now and waiting) the DSL part of the line has dropped 3 to 4 times so far, and this is only what we have noticed. Aside from the the normal white noise that is on the phone there is occasionally beeps that sound like/similar to what a dial-up modem makes on the line.

 

[angotull]

Roll on fiber replacement - man I wish