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Do ADSL Filters "expire"?


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Old 05-06-2011, 15:04
stu0rt
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My friend was having problems with his broadband cutting out every few hours. His ISP told him to replace the ADSL filter because they get "clogged up" over time. The way they described it was like a water filter needing replacement every so often.

Personally I think that's a ludicrous suggestion, but what do I know? He did replace the filter and hasn't had any problems since, but I suspect it was just the act of rebooting the router that actually solved the issue, not the new filter.
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Old 05-06-2011, 15:16
carguy143
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Filters can fail i believe. They don't have any moving parts though. Most ISPs would start with diagnosis by replacing the cheaper items first such as filters before the router.
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Old 05-06-2011, 15:28
spiney2
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Like you say, that's just ignorant rubbish.

an ADSL filter is 1 or 2 or more pole pasive network high pass, to stop lower telephone frequencies breaking through into ADSL passband. How effectively, depends on design ....... the more components, the steeper the cutoff.

http://www.adslnation.com/support/filters.php

(the 2 diagrams above show a very basic1 pole low pass for phone, and 1 pole high pass for modem! They look cimplex because a balanced circuit, but basically just single pole .... ).

The more "zeros" a passive high pass filter has, the steeper the cutoff. Here's an good account of similar Butterworth (low pass, not high pass!) passive filters .......

http://en.wikipedia.org/wiki/File:Bu...ter_Orders.svg

http://en.wikipedia.org/wiki/Butterworth_filter
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Old 05-06-2011, 15:39
chrisjr
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Actually an ADSL filter is a low pass design to remove the high frequency ADSL signals from the phone connection on the filter. The modem has a built in high pass filter to remove the voice signal which is why it is wired directly to the phone line.

Electronic filters do not clog up. There is after all nothing to clog them up anyway so comparisons with water filters are just plain nonsense. The components used to make the filter can degrade or fail over time. But a properly designed filter with good spec components will last for years.
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Old 05-06-2011, 17:21
spiney2
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That's rubbish. There is no point in "removing" high frequencies from the phone, since they can;t be heard anyway! Where only a single low pass filter is used, the issue is mainly impedance matching.

"The ADSL POTS splitter is simply a series of coupled inductors and parallel capacitors forming a low pass filter that attenuates the higher frequency ADSL data and permits only the voice frequencies to reach the telephone. The series inductor shows high impedance to high freuquencies, so the ADSL signals on the line are not attenuated.! "

(in other words, if ADSL signals "appear" at phone earpiece, then they're lower power outgoing, and modem speed is reduced!).

http://www.epanorama.net/documents/t...sl_filter.html

Filters can be more complicated, with some non passive ones using op-amps & 4 quad multipliers, powered from the line 50v ........

The components for either passive or active filters are long term stable. The only problem would be electolytic caps, which are used in the active versions for power decoupling only, not the filter circuit.
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Old 05-06-2011, 17:44
spiney2
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...... in fact, the "low pass filter" is really a high pass filter, upside down! It's done that way round, because, a passive high pass filter involves either a capacitor which won't pass dc, or an inductor with a large resistor, cutting mike and earpiece power on the phone.
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Old 06-06-2011, 09:15
The Sack
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My friend was having problems with his broadband cutting out every few hours. His ISP told him to replace the ADSL filter because they get "clogged up" over time. The way they described it was like a water filter needing replacement every so often.

Personally I think that's a ludicrous suggestion, but what do I know? He did replace the filter and hasn't had any problems since, but I suspect it was just the act of rebooting the router that actually solved the issue, not the new filter.
Filters can fail but not by getting clogged up like the filter in your tumble drier. Dry joints on cheapo filters are probably the most common cause.

All electrical componants degrade over time but unless a capacitor pops it wont be enough to bugger it up.
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Old 07-06-2011, 14:10
spiney2
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Yeah!

Filter components will be metal film resistors, mica or poycarbonate or foil caps, and wire inductors. Very stable.

Electrolytic caps anre the bad guys, but only used for decoupling, not the filter.
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Old 07-06-2011, 14:20
Psion123
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Biggest failure in filters, as in most modern electronic equipment is failed soldered joints due to the mandatory use of lead free solder in production processes. Filters do not clog up. Filters are Low Pass towards the phone itself and high pass as regards the modem & ADSL signal.
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Old 07-06-2011, 15:32
cnbcwatcher
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Not sure but we're still using the ADSL filter we had plugged into the line since we got it and it hasn't shown signs of failure yet. I doubt they last forever though, they probably do fail at some point.
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Old 07-06-2011, 15:37
spiney2
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the basic filter is just passive components. nothing to fail.
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Old 07-06-2011, 15:44
Bill.Moo
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This reminds me of the time many years ago when I was told by Sky Support to remove the scart lead from the back of the decoder and give it a shake!

(Conveniently, it took long enough for them to send a reset signal I think!)

--
Bill
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Old 07-06-2011, 16:30
soulboy77
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I think I'll start a new business charging people for unclogging their ADSL filters!
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Old 07-06-2011, 16:43
hardylane
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That's rubbish. There is no point in "removing" high frequencies from the phone, since they can;t be heard anyway!
Absolute drivel.

What do you think they use, ultrasonics?!

You can hear the high-pitched ADSL carrier on a phone if you don't use an ADSL filter.
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Old 07-06-2011, 17:46
The Sack
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the basic filter is just passive components. nothing to fail.
But yet they do.
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Old 07-06-2011, 17:51
The Sack
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Absolute drivel.

What do you think they use, ultrasonics?!

You can hear the high-pitched ADSL carrier on a phone if you don't use an ADSL filter.
The lowest frequency use with ADSL is 25'ish KHz which to be fair is way above what most people can hear. Some people below 20 years old with exceptional hearing might be able to hear it but i would be surprised.
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Old 07-06-2011, 17:55
hardylane
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The lowest frequency use with ADSL is 25'ish KHz which to be fair is way above what most people can hear. Some people below 20 years old with exceptional hearing might be able to hear it but i would be surprised.
I'm in my 40's and can still hear it... especially the training process.

I think you're perhaps generalising a bit.

Example: http://www.youtube.com/watch?v=6K_aIft9Nmo
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Old 08-06-2011, 07:04
noise747
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Got a 9 year old filter on the extension, still works, i have been plugged into the cable, but not beeused as such for 2 years, started to use it again a couple of weeks ago when I moved the phone.

A friend of mine is still using the origitanl BT filter faceplate that was put in 11 years ago and still works, mine is in a box somewhere as I changed it to a different make thinking it may be better.
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Old 08-06-2011, 07:12
davews
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The lowest frequency use with ADSL is 25'ish KHz which to be fair is way above what most people can hear. Some people below 20 years old with exceptional hearing might be able to hear it but i would be surprised.
What happens is that the high ADSL frequencies get rectified by components inside the phone resulting in frequencies within the audio passband and are hence audible. Just remove a filter and have a listen.

And yes filters DO fail, I have one here which I believe has a leaky capacitor. There is 50-70V across the components from the phone line which has probably caused an out of spec cap to fail.
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Old 08-06-2011, 08:18
Glawster2002
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Such a heated debate over something so simple!

An ADSL phone line can carry two separate types of traffic, a low frequency component, a voice telephone call, and a high frequency component, Internet traffic.

Some people can hear both components, which would obviously have a big impact when trying to make a phone call, so an ADSL filter is fitted to remove the Internet component from the voice circuit.

As an ADSL filter is an electronic circuit it can, and very occasionally does, fail.
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Old 08-06-2011, 08:33
neo_wales
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They do fail, one from BT failed but a d-link I've been using for several years is still fine.
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Old 08-06-2011, 08:39
noise747
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They do fail, one from BT failed but a d-link I've been using for several years is still fine.
Normally the cheap ones fail, as i said I use a filter faceplate, just one other filter for the extension, so I don't really use any other filters. But some people I know have got cheap filters that they got from ebuyer or other places for a couple of quid each and most of them have failed.

Best to buy good ones, but saying that some that comes with routers are fine.

got loads of the things now, two came with my BT home hub, two with my speedtouch, one with my netgear. I also got 4 or 5 of them in a box and I have no idea where they came from.
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Old 08-06-2011, 14:37
Ray266
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Yes true they can go faulty, we had to call BT out as our home phone was hissing & crackling all the time knocking the internet off even bought a new set of cordless phones, when I thought of changing the filters the crackling stopped & all was ok pity I didn't check the filters before buying new phones
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Old 08-06-2011, 15:41
neo_wales
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Normally the cheap ones fail, as i said I use a filter faceplate, just one other filter for the extension, so I don't really use any other filters. But some people I know have got cheap filters that they got from ebuyer or other places for a couple of quid each and most of them have failed.

Best to buy good ones, but saying that some that comes with routers are fine.

got loads of the things now, two came with my BT home hub, two with my speedtouch, one with my netgear. I also got 4 or 5 of them in a box and I have no idea where they came from.
Cheap BT kit then, it was their filters that failed me.
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Old 08-06-2011, 19:01
spiney2
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As I tried to say, the point of an upside down low pass filter is, pretty much, maximium ADSL power transfer. Thus approaching the Shannon Limit closely as possible, given the system used.

Granted there's IMD, nobody's too woried about slight distortion of 400-3500 Hz speech! It's reasonable, because the ADSL spectral power density is small. It's not like the whopping big AC bias used in analogue tape recording .......

As for failures, in my experience it's usually corrosion caused by 50v electrolytic action on the components, especially the printed cct foil ...........
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