Despite a complete check of the whole link, from here to the Dslam I get it even with three filters in series..
It disappears when the router is switched off.
Every joint is a nice little mixer, and enough of the RF intermodulation products are in the audio band for it to be permanently audible.
Roll on FTTC...
I repeat, the intermodulation is NOT in the phone, its in the line. Or probably in the joints in the line.
As proven by adding extra RF filtration.
If anyone can hear any hiss which is 50dB down, then they must have extremely good hearing.
Thats not right. Your saying a phone plugged into your phone line thats got an ADSL signal thereon despite Three I presume, series connected filters in and it still has a pronounced audible hiss?...
Umm .. out your way;?..
You overhead fed or underground?..
You ever put a proper spectrum analyser on that at all?..
You forget I used to configure ADSL for demos. I have installed many with and without filters. I only ever got noise on one phone and that was an old pulse dialler that I binned (the VoIP termination unit/soft switch didn't support pulse dialling so it didn't work anyway)..
You need a new phone.
I don't suppose he has worked out that the RF originates in the exchange, travels down the line, gets rectified by the dry joints to give the audio component, arrives at the house, where he adds extra RF filtration to do what to the audio noise? Or maybe he has broken into a street cabinet?
Yep!
well they done got it in Bury which aint over 10 mile thataway->
Both
Nope. Dont have one.
ADSL is fine. VOIP is fine. Phone is as clean as a whistle with no router on it.
No noise at all.
Put the router on, and there's about 10dB above background on it.
really?
ring the other one. Its got bells on.
Yu need a better phione and better ears
Sigh. Perhaps the *main* purpose of an ADSL filter is to remove the noise from the line when using a phone.
Hope no-one asked you any questions at your 'demos'.
There are phones out there that are affected by presence of ADSL carrier. This is not a theory, but something proven in practice. So far I have only ever uncounted it on systems missing microfilters where they should have been, and adding the filter has fixed it.
Some systems will exhibit a little bit of noise breakthrough from the ADSL training phase, if a router is started while a voice call is in progress - however that normally vanished once the modem has sync.
Had a similar experience with a customer once. I was remote controlling a machine. and told them I would ring you back when it is fixed. Then every time they hung up, I lost remote control and had to ring them back again to re-enable it. I suggested they had their filter in the wrong place, which they were sure they did not!
Only finally fixed it next time I was on site and took apart the mess of extension leads, four to one adaptors, and rearranged the sequence so that both the phones were on the filtered side rather than just one.
This is actually observable, especially on long rural lines - you need a router that can show a graph of the ADSL parallel tones that are currently in use (or at least report the bit to tone allocations). You often see a marked change at night when some of the tones which have to be excised correlate exactly to the broadcast frequency of some of the higher powered continental radio stations.
(making sure you don't have an unbalanced "bell" wire helps reduce the effect)
Alas there are obviously phones out there that have not sought your agreement, because I have observed the effect Peter describes on several occasions.
Not that much. Note also that the audio equipment in a modern phone will have a very much wider bandwidth than that of the telephony channel.
Possibly true, but not always a popular suggestion it has to be said.
Would not be much use if it did, since you need it to reach the modem.
Have you forgotten that just because something is outside of your experience, it is not precluded from happening?
The last phone I had noise problems with was a modern Panasonic DECT cordless phone.
Line is about 2.5 miles underground apart from the last few tens of meters. Variation in overall SN ratio day to night is at least 6dB sometimes more.
When I did my experiment I had a variety of phones in the house. Including the original BT supplied cabled one. And cordless - both analogue and DECT. They all produced the same annoying noise to a greater or lesser extent. What I haven't tried is a corded phone into the sort of socket that has direct access to the line and disconnects the house wiring, as I didn't have one at the time. But then changed to one with built in filter, and situated the router beside it. Since this sorted everything I lost interest in further experimentation.
Bigger sigh. Just exactly how is the filter going to remove the noise from the line when the noise is audio frequencies? If you filter it out then there will be no sound at the phone which sort of makes it useless.
If its the ADSL frequencies then why is the phone converting them to audio in the first place? If it does then get a better phone.
As I have stated in the past the filter is to stop the line changing characteristics when great lumps of stuff are switched across the line. The ADSL will still work with a phone across the line but it will retrain every time you pick up/ hang up resulting in breaks in the data.
I am sure you couldn't have asked one that made sense.
I wonder /how/ these things get that way though? Whenever I confront something like that (and have done many-a-time when I was a Field Support Tech and when helping friends and family etc) I like to 'understand' how it's all connected together first / currently. So to do that I might first unplug one thing at a time, clear the lead back to where I can see it all then plug it back in and move on. Once I have a picture of how it is now I would then be able to clearly see if there were any technical issues with how it was and make adjustments accordingly. I've seen people randomly unplugging and re plugging stuff when there is no way they could actually know what went to what, even if they understood what was supposed to be where.
Like the 'can't get on the Internet problem I resolved (in about 10 mins) for a neighbour recently when the cable modem and router PSUs had been transposed (amongst other things) and causing all sorts of weird effects. I did exactly the same thing there ... traced everything back to where it came from and just plugged it all in correctly. The irony was then it 'just worked'.
Maybe a bit I take for granted in all this is that I do have an understanding of how stuff fits together and they simply don't. I just can't see how they don't! (Well, I do of course because there are things I'm not interested in or good at but they are normally things where you might not be able to use a bit of common sense / lateral thinking). ;-)
Cheers, T i m
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