Forum Home
Press F1
Thread ID: 71582	2006-08-09 23:22:00	Phone buzz	linw (53)	Press F1

Post ID	Timestamp	Content	User
477495	2006-08-11 00:26:00	With a 3 wire system, the 3rd wire (the old "ringing circuit") can give noise problems. Both noise to phones and radiating out of the lines to nearby radios.Does it, in fact, GF? It's just connected to one of the line wires with a 2uF capacitor in the Master block. So effectively, it's just another wire in parallel with that line. It only carries any real current when ringing signal is there and there's an old style phone which has a bell between it and the other line wire. It might cause some unbalance for the RF of ADSL, which is why Telecom don't approve of it, but at audio frequencies it surely doen't have much effect.	Graham L (2)
477496	2006-08-11 00:39:00	Does it, in fact, GF? It's just connected to one of the line wires with a 2uF capacitor in the Master block . So effectively, it's just another wire in parallel with that line . It only carries any real current when ringing signal is there and there's an old style phone which has a bell between it and the other line wire . It might cause some unbalance for the RF of ADSL, which is why Telecom don't approve of it, but at audio frequencies it surely doen't have much effect . It is not a balanced or "twisted" cable format so it is prone to pickup of low frequency mains-borne noise . It is highly unlikely to be anything to do with DSL or filters etc and the ringer wire and cap just serve to unbalance it further via a series inductive/capacitive loop . The buzz will almost certainly emanate from mains cables running near phone wiring somewhere in the installation . To prove the point, just kill the power at the main switch and check the phone for noise . Provided that the coupling is after the main switch, the noise should stop . I had one length of old 3-wire left in my house after renovation and although converted to 2-wire, that phone always buzzed . I couldn't get into the wall to replace it, but in the end I managed to rewire it from another source using twisted-pair cable and that fixed it . Cheers Billy 8-{)	Billy T (70)
477497	2006-08-11 00:39:00	You only hear the signal after it has been through your phone. The phone electronics must respond to the high frequencies to produce the audible noise. Edit: Some older internal cable either wasn't twisted pair or had a lazy twist. Later cable used the same layup as Cat 5 but fewer pairs.	PaulD (232)
477498	2006-08-11 01:00:00	Whew, lots of interesting info . Thanks, guys . The buzz I speak of is definitely from the ADSL connection as it is not there when the modem is powered off . It also occurs with only one phone connected . Most of the cabling would be 30 yrs old . Maybe it doesn't have correct twist characteristics? The filters were supplied by IHUG so I just assumed they would work . If these filters are OK I guess we have to assume the house wiring is crap . Sounds like a call to a phone tech would be a good idea!	linw (53)
477499	2006-08-11 01:26:00	I would suspect the filter(s). Have you tried 1 phone with each of the filters to see if there's a difference. I can't see Ihug paying more than they had to for a filter ;-) You don't need balance problems to get a noise source, the ADSL signal is already on the line.	PaulD (232)
477500	2006-08-11 02:08:00	The buzz I speak of is definitely from the ADSL connection as it is not there when the modem is powered off. It also occurs with only one phone connected.The adsl signal is present on your line regardless of whether you have a moden connected or not, and your phone signal precedes the modem, so if you get noise with the modem on and none with it off, it is likely to be the modem that is inserting the noise, not the adsl signal per se. The filters are a low-pass system, allowing speech frequencies through to the phone but not the high frequency adsl signals, so the symptoms you describe point toward a defective modem, or low frequency adsl data-demodulation artefacts being injected back into the phone line. Does the character of the noise vary at all when you are downloading data? If it does, that would suggest demodulation artefacts, but if it doesn't, it would suggest that it is the modem itself that is generating the noise. Of course that depends on the cause and effect relationship being logical, and I have given up counting how many times I have diagnosed the logical reason for a fault or problem, only to discover that it is totally illogical when I finally locate the cause! Another reason could simply be your modem too close to your monitor, so check noise levels with the monitor off. I shall watch your progress with interest. :) Cheers Billy 8-{)	Billy T (70)
477501	2006-08-11 02:19:00	Post deleted as due to forum lag it was covered....	godfather (25)
477502	2006-08-11 03:12:00	The adsl signal is present on your line regardless of whether you have a moden connected or not, and your phone signal precedes the modem, so if you get noise with the modem on and none with it off, it is likely to be the modem that is inserting the noise, not the adsl signal per se. The filters are a low-pass system, allowing speech frequencies through to the phone but not the high frequency adsl signals, so the symptoms you describe point toward a defective modem, or low frequency adsl data-demodulation artefacts being injected back into the phone line. Billy 8-{) Without a modem the DSLAM is most likely to stop sending anything other than a periodic wakeup tone to get the modems to synchronise if present. The modem does send the lower group of ADSL frequencies which are used for upload and are the ones most likely to get through a filter that doesn't cut off sharply. The same frequencies can interfere with AM radio.	PaulD (232)
477503	2006-08-13 00:59:00	Thanks again, guys . And, Billy, I empathise with what you said about being careful of following logic!! Went to my friend's place yesterday and I think he basically needs his wiring checked thoroughly . We tried with all but one filter/phone disconnected and moved the phone around . One phone jack seemed to trigger the noise problem the worst . Told him to get the whole place re-done with 2 wire sockets . With the place mapped out it shouldn't take much time, really . Thanks for the learning experience - there is always an expert in most fields here!	linw (53)
477504	2006-08-13 02:32:00	. . . I had one length of old 3-wire left in my house after renovation and although converted to 2-wire, that phone always buzzed . I couldn't get into the wall to replace it, but in the end I managed to rewire it from another source using twisted-pair cable and that fixed it . That was one length of inaccessible cable so you don't know what its condition was . If the system had been converted to 2 wire, the third wire was not connected . Therefore, it was doing nothing . The two line wires were a balanced pair . IT IS BALANCED IF ONE WIRE PULLS WHILE THE OTHER IS PUSHING . Balance has got nothing to do with whether a pair is twisted . Twisting is a means of controlling the impedance and reducing coupling between pairs in multipair cables . The hidden wires might have had some twisted joints, which can grow into copper oxide rectifiers over time . It might have been supported by mains wires . ;) You don't know . It was a fault in a section of wire . Three wire systems were used for many years . It doesn't guarantee hum or buzz . A lot of problems are caused by the fact that modern phones are not real telephones . Real phones worked reliably over iron wires, single wire with earth returns . The modern ones are full of electronics, and there's no RF shielding . If you connect an ADSL modem sending 2MHz signals through a 2 uF capacitor to a wire which runs close to the balanced line feeding the phones, it's quite likely that some phones will work as radio receivers . The filters will cut the RF from the balanced line, but the handset wires are a good aerial . (Any ADSL noise is going to come from the local end . . . the signals from the exchange are probably 20 or 30 dB down after their travels . ) Billy solved his problem by replacing the wires . You might do the same . It's like formatting and reinstalling Windows, or "loading the latest drivers" . :) "I did this and the problem went away, therefore . . . " (jonathan . mueller . faculty . noctrl . edu/100/correlation_or_causation . htm) The simplest, quickest, and cheapest first thing to do is to go to the "Master" block, and disconnect the ringing wire . The wires being used are on connections 2 and 5 on the block (the middle conection on each side)	Graham L (2)
1 2 3