Telephone Experts Please - Part 2

[dennis]

Yes I do know that. But that is a problem with the phone, not the line or the ADSL or the filter. You may reduce the ADSL signal and broadcast radio break through by fitting the filters but it will never be quiet even without the ADSL.

It will also be cheap to fit well designed electronics that reject the noise.

IME phones that are badly designed and are susceptible to noise also radiate the noise and can reduce broadband performance by a lot.

Try telling that to TNP, ADSL appears to be well beyond his ability to understand.

[dennis]

I never said it hadn't happened to me, see below.

So send it back and tell them to fix it.

[tony sayer]

Humm .. don't get this on our dodgy naff Virgin Media connection yer know;)...

[tony sayer]

How exactly do they radiate noise then ?.

What noise, frequency range and bandwidth and power?....

[tony sayer]

Not right Guv...

Yeabut your miles from there and out "there" too so ;(...

[tony sayer]

What Router make and model is that then?..

[Dave Plowman (News)]

I'd suggest you look at basic phone design. If you could understand it. It shows why a high level RF signal on the line appears within the audio band.

Right. So the same phone filtered became useless? perhaps you should get in touch with the filter makers - they'll be delighted to act on your findings.

Thanks for making it obvious you've never looked at the phone circuits in use at the introduction of broadband.

Given the cost of a filter versus a new phone...

How wrong you are as regards the primary purpose of the filter at the start of broadband.

Did BT insist you get a new handset when ADSL was installed? No? Have you ever wondered why?

[dennis]

The same way as anything else, bits of circuitry/wire acting as aerials + capacitive coupling + loads of other ways.

Or did you mean how do they generate it? That would include cr@p DC-DC convertors, transmitters, etc. Even the microprocessors can generate noise.

Your guess would be as good as mine. If you have a particular phone in mind you could measure it.

[dennis]

Stop being obtuse, you know perfectly well what I said.

Ah so we are talking antiques now.

No, that is why it was there. You couldn't sell broadband if it broke every time there was a call.

No, I never had to wonder why, its fairly obvious why.

[Dave Plowman (News)]

You couldn't sell it at all with that dreadful noise on the phone. Hence every router coming with at least one filter. When it was introduced, mobile phones weren't the main phone in use unlike today.

[Peter Crosland]

The first thing is to methodical and systematic. Only change one item at a time otherwise misleading symptoms may confuse the issue. Plug a phone that you know to be working satisfactorily into the test socket (The one behind the removable faceplate) without any filter then dial 17070 and select option 2 (Quiet line test) that enables you to listen to the incoming line for any extraneous noise. If that test is satisfactory then you need to try each piece of equipment in turn to isolate the problem. You might try each filter in conjunction with the phone plugged directly into the test socket.

Peter Crosland

[tony sayer]

In article , dennis@home scribeth thus

Such as?..

In a phone?, do tell more..

That much RF noise?..

And thats prolly the best it is your guess;!...

[The Natural Philosopher]

Any of the 4 I have tried.

It's low level, and perhaps others don't notice it.

But my phones are quality and PABX fed, so I do...

[The Natural Philosopher]

The main function of an ADSL filter is actually to prevent ADSL signals from being crapped on by domestic equipment that represents a dead short, or worse at RF frequencies. It should not be called a filter at all..its more a frequency sensitive splitter.

[The Natural Philosopher]

Quite.

?

It isn't. Its the phone LINE that is doing that.

[The Natural Philosopher]

It isn't a dreadful noise. Its a low level hiss.

[The Natural Philosopher]

Studies show that the main cause of interference is other peoples ADSL, with LW and MW broadcasts being the second highest.

[The Natural Philosopher]

I get a steady 3dB variation on about 1.5 miles

[The Natural Philosopher]

On the contrary, I understand it intimately.

I also know what's happens to a broad RF spectrum when you run it down anything non-linear.

I dint spend 20 years doing audio and RF desing without learning something..

[The Natural Philosopher]

Well I am happy with my 4.5Mbps speed at the moment.

Which is better than many get inside cambridge....