Hi Folks,

A strange thing happened today. My normally working fine ADSL connection
decided it couldn't sync to the exchange signal (we'd had a lightening
storm on Wed and had done something nasty to the BT system - it was only
fixed yesterday so I was rather suspicious that all of a sudden my
broadband had failed)
To cut a long story short, I was advised by my ISP (Demon) to try
another microfilter as they had run a test and it looked as if there was
no filtering happening. I said that it couldn't be that as I had tried
the modem 'straight through' with nothing else connected on the line -
the tec support person said I HAD to use a splitter.

I wasn't convinced as I thought that the microfilters were effectively
low pass filters for the voice side and I'm sure I've read you don't
need one if there is nothing else connected, and also, I've been using
it fine with the modem directly connected and just the phones connected
via the filters!

But whatever, I gave it a go....... and bugger me..... it now works!!

Can someone tell me what's going on??

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No

A microfilter does nothing for the ADSL side, you don't need one.

The only thing a microfilter does is filter the DATA high pitched traffic
out for a voice line.




"Gareth Jones" <usenet@nospam.demon.co.uk> wrote in message
news:7MW+TrHYSqGAFwtB@nospam.demon.co.uk...

On Fri, 30 Jan 2004 18:38:16 +0000, Gareth Jones
<usenet@nospam.demon.co.uk> wrote:

one possibility is that the filter was keeping some crap away from the
modem by filtering it - if a phone or some internal wiring is HF noisy
the low pass filter will keep that away from the ADSL modem, providing
the offending item is plugged into the voice side of the filter.

Is the experiment repeatable ? if you take the filter out of circuit
does it stop working.

Phil

In message <du9l10tjqoi8l4mrclh7ivo9ru2o1q4mfm@4ax.com>, Phil Thompson
<cynical_observer@hotmail.com> writes
But as I mentioned, I had tried it (two different modems in fact)
straight through with NOTHING else connected !!

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Gareth Jones <usenet@nospam.demon.co.uk> wrote in
news:lf6JXkIp$qGAFwOU@nospam.demon.co.uk:

I can't account for what you have observed, but I can add some
information on what splitters do in case that helps.

It is important for legacy analogue kit to be connected via a
splitter because:

1) The analogue kit may perform badly because of interference from
the high-frequency ADSL signal e.g. audible background noise on a
phone call.

2) The analogue kit can generate high-frequency noise, e.g. from
mechanical switches that disrupts the ADSL equipment.

Reason 2) is what many people don't appreciate. For example:
picking up the receiver for an incoming phone call may cause the
ADSL connection to drop if the phone is not connected via a
splitter.

In an ADSL splitter, the ADSL path is a straight-through electrical
circuit and it's only purpose for an ADSL modem is to provide a
RJ11 socket interface to the phone line.

--
BRG
===
http://www.brgservices.co.uk/

On Fri, 30 Jan 2004 19:26:33 +0000, Gareth Jones
<usenet@nospam.demon.co.uk> wrote:

not knowing your system I wondered if there was extension wiring
connected that could be a problem - one guy could only get ADSL to
work straight off the master socket, reconnecting the extensions
(without anytihng plugged in) killed it off.

is it repeatable ie if you take the microfilter out now does it stop
working ?

how do you connect the modem without the microfilter - via an RJ11-BT
adaptor or how ? and does the microfilter have an RJ11 output for the
modem ?

Phil

Gareth Jones <usenet@nospam.demon.co.uk> wrote in message news:<lf6JXkIp$qGAFwOU@nospam.demon.co.uk>...
Firstly Lightning does very strange things to circiuts, and very often
the componants take a few days to break down.
As to you problem, you say it works fine with no filter. but with a
filter it doesnt. Is this all filters or just one.
For your modem you dont need and to be honest shouldnt use a filter if
at all possible. for phones you will need a filter. It sounds as if
the filters go a bit of a spike and are no kaput.

Plug your modem in on its own if alls well add 1 filter at a time, if
it stops working that is the offending filter, if its still working
plug 1 phone in at a time etc.

Ian

www.cyber-cottage.co.uk

Gareth Jones <usenet@nospam.demon.co.uk> wrote in message news:<lf6JXkIp$qGAFwOU@nospam.demon.co.uk>...
Firstly Lightning does very strange things to circiuts, and very often
the componants take a few days to break down.
As to you problem, you say it works fine with no filter. but with a
filter it doesnt. Is this all filters or just one.
For your modem you dont need and to be honest shouldnt use a filter if
at all possible. for phones you will need a filter. It sounds as if
the filters go a bit of a spike and are no kaput.

Plug your modem in on its own if alls well add 1 filter at a time, if
it stops working that is the offending filter, if its still working
plug 1 phone in at a time etc.

Ian

www.cyber-cottage.co.uk

Phil Thompson <cynical_observer@hotmail.com> wrote:

: how do you connect the modem without the microfilter - via an RJ11-BT
: adaptor or how ? and does the microfilter have an RJ11 output for the
: modem ?

The microfilters DO have an RJ11 output for the modem. As you suggest a
simple BT->RJ11 convertor will work just as well.

On 31 Jan 2004 08:57:27 GMT, Brian McIlwrath <bkm@bkmpc.bnsc.rl.ac.uk>
wrote:

I was wondering how the OP's "direct" connection was made. His modem
might have a BT plug but in either case there's an adaptor in there
that may be an issue itself.

Phil

In message <gkum105nj0uovlb0dd8mekengueqa27cbt@4ax.com>, Phil Thompson
<cynical_observer@hotmail.com> writes
Ok, some confusion here from some (other) posters, so I'll try to
clarify:

I had a standard extension lead going straight from the master socket to
the ADSL modem via a BT > RJ11 lead. Nothing else in the property
connected. Worked fine.
So I know the ADSL modem can work 'straight through'

I then put a couple of normal t-piece splitters (no filters) in the
system and used a microfilter wherever a phone was to be connected - the
modem is thus still 'straight through'
Worked fine.
(I'm on the limit of distance so was getting steady 59db attenuation -
measured by two modems I have and the BT PTO!)

After an electrical storm, BT had to do some repairs, the phone was OS
for a day.
When it came back, my attenuation figures are wandering around - but now
in the low sixties - but the modem was still working fine.

Then the modem connect light went off and could not reconnect (with
either of my two modems)
I disconnected _everything_ except the modem - still nothing.
I stick a microfilter on the end, and connect the modem via the correct
RJ11 connector on it - voila! The bloody thing start to work!?!

So the microfilter must be doing _something_ - I'm just curious as to
what??

If its true that the ADSL port of the microfilter is indeed a straight
pass through, The only theory I can come up with myself at the moment is
that BT have changed something, my line is now operating on the limit
(its 61.1 db and 9.4 SNR as I write) and yesterday, it drifted out of
spec and stopped working (I had seen 64db in the morning)
Maybe putting the microfilter on was enough to change the
characteristics of the line (via the tapped low pass filter) to just
bring it back into operating range???

???
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On Sat, 31 Jan 2004 10:23:41 +0000, Gareth Jones
<usenet@nospam.demon.co.uk> wrote:

if you look at the diagrams at the bottom of
http://www.adslnation.com/support/filters.php you'll see that there is
circuitry across the straight through pair, for example at least one
inductor and a capacitor in series, this may be enough to reduce the
noise on the line, bringing your SNR up to the level where the modem
can work.

The modem circuitry will have a high pass filter in it, the
implication of your observation is that the addiiton of the
microfilter circuits in parallel with it are improving the SNR in some
way.

Phil

In article <bve8fv$r8aa6$1@ID-133922.news.uni-berlin.de>,
PhilÅ <iclgateway@hotmail.com> wrote:
Untrue. It ensures that the impedence and capacitance seen by the modem
are constant. If you don't use one, the modem will almost certainly
retrain every time the phone goes on and off hook. There was a
specification for rapid-retrain DSL (G.dmt, from memory) designed such
that the retrains were negligible, but that's not been implemented in
the UK.

ian

On Sat, 31 Jan 2004 16:52:30 +0000 (UTC), Ian G Batten
<I.G.Batten@batten.eu.org> wrote:

that's an argument for having one on the phone connection. If there is
only an ADSL modem on the line then this argument doesn't hold.

Phil

In article <4pvn10ljmjrsb4nqbuk5kdf5of5kr5d0t2@4ax.com>,
Phil Thompson <cynical_observer@hotmail.com> wrote:
Correct.

ian

In message <bvl7mk$h19$1@news-out.ftel.co.uk>, Ian G Batten
<I.G.Batten@batten.eu.org> writes
But that still doesn't explain the fact that I could only get my modem
to sync when there was a microfilter plugged in and it was ONLY the
modem connected to the line.
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In article <jAc4whN0okHAFwG3@nospam.demon.co.uk>,
Gareth Jones <usenet@nospam.demon.co.uk> wrote:
Ah, I'd missed that part. A wild guess would be that there's something
about your domestic phone wiring so toxic that the filter keeps it at
pay. What happens if the modem is plugged into the master socket, and
all other customer-side wiring is disconnected?

ian

In message <bvlje4$k25$1@news-out.ftel.co.uk>, Ian G Batten
<I.G.Batten@batten.eu.org> writes
Read the post. There is nothing else plugged in!!! Nothing else.... the
modem was the ONLY thing plugged in....

And the wiring isn't toxic. Its new, I know exactly where it going,
We've just built the house ourselves!
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How does that mean there are no wiring faults?


SJW
A.C.S. Ltd.

In message <401ec81b.429523742@news.dsl.pipex.com>, Lurch
<iam.not@telling.you> writes
Because when I plug something directly into the master socket, I KNOW
where the cable is coming from, I KNOW some other previous owner hasn't
run some dodgy extension into it therefore there ARE no additional wires
for there to be faults on!!

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