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On Mon, 21 Oct 2013, Julian Hall wrote:
When I was working ISP Tech we were told that all devices on the same circuit need filters, so if you had two phones, a fax machine and an answering machine on the same circuit, that would be four filters. Our first step in diagnosing problems was always to disconnect everything else in the house, and only connect the modem/router. If you still have a problem then try a new filter, and if it persists that exonerates the filters. Of course the more filters you have in use the more chance one of them could develop a fault. That's a spit under 10 years ago so things may have changed since then and less needed, but even so I agree with those who said it's the first thing to check.
It's fine advice and easy to script and take someone through...But in Neils case, his line maintains sync. speed so issues are more likely to be remote to his house.
Why people go down the route of checking filters first rather than line speed, SNR, etc. beats me. It's probably easier when dealing with Joe average, I guess.
ADSL filters exist to stop the higher frequency ADSL signals interfering with the phone (and not neccessarily the other way round, but by their nature that happens too) ADSL modems are more than capable of filtering out the lower frequencies a phone uses.
ADSL is a set of wibbly wobbly frequencies starting at about 25KHz and extending up to about 2.2MHz (depending on the technology used). This is carried over the copper wires from the exchange to your modem.
Telephone audio is a set of wibbly wobbly frequencies from about 0 up to a max of 4000Hz.
So the 2 frequency bands are normally quite separate anyway, however the input wibbly wobbly separators in a standard phone (the 'hybrid' separates/mixes the 2 directions from 2 to 4 wires) can start to demodulate some of the higher wibbly wobbly stuff and you might hear hiss/whoosh type noises in the phone.
I have a test phone with a high impedance input mode and using that, I can tell if an unfiltered line has a "live" ADSL signal on it... (or the filter is broken)
So normally there is a filter before the phone (or for the ancient, fax machine).
You don't strictly need one filter per device, it's one filter per wire pair from the master socket. So you can fit a master socket filter, then all the phones in the house are filtered and don't need local filters. The master filter plate has a separate (unfiltered) socket for the ADSL modem to connect into. This is by far the best way to do it. It keeps the wires to the modem as short as possible and makes sure that any internal phone wiring is pre-filtered, however you can only then plug a modem into the master socket, but it really is the best way to do it.
Sadly, some houses have shockingly bad phone wiring, so the advice of one filter per phone socket is the easy way to do it - and in the early days, master socket filters were few and far between.
Anyway, this isn't rocket science - it should be obvious to those on the list at least.
So if you have an ADSL issue - check your router/modem first. See what your line sync. speed is. If it's normal for your line (it will be marginally higher than the best speedtest you've ever done) then start to look elsewhere, but if it's much much lower, then start to look at your local wiring. Unplug all phones, connect into the master socket, etc.
And if you don't have a new style (as of about 25 years ago) master socket, then get one and fit it yourself. Do a neat job and don't tell BT and they'll be none the wiser, but cock it up and expect to pay them over £100 to fix it )-:
This: http://www.tlc-direct.co.uk/Products/GPNTE5ADSL.htmlor something like it is the device to fit over the standard BT NTE5 to give you the best possible performance of your ADSL signal - the down-side is that you need to put your modem near the master socket, but so what? Cat-5 is digital after you get rid of all that wibbly wobbly stuff. Just run it to a new switch and Wi-Fi access point if needed.
Gordon
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