Newsgroups: sci.electronics.misc
Subject: Re: DSL
References: <[email protected]>
bi_teendude17  writes:

> Hello,
> 
> I just installed DSL and even though I can use DSL and analog
> simultaneously, it seems like DSL filters that must  be installed at
> each telephone that is connected to same line as DSL, except for DSL
> modem itself, are lowering the analog thruput of the line.  Before DSL,
> I was able to attain 49,333bps with my laptop and with all these
> filters  I can only get 21,600bps from that line.  I am assuming this is
> due to filter absorbing up high-range of the modem communication.  Does
> this sound nomal and is this one of the secret they don't tell you
> about?

There are two thing which might affect the throughput. First
which you mentioned could be the effect of the filters itself so that
they change the frequency response of the telephone line which
lowers the available speed. This is possible, but I don't think
that very likely, because the cutoff frequency between normal
telephone line and lowest ADSL frequency can be quite much higher
than highest telephoen frequency, so the filter if well designed
shoudl not much affect the response on normal telephone band.

The other thing which might be more of the reson is that those
filters are not ideal and ADSL system adds very much signal to the line.
If those filters still pass some part of it to the line, it would
cause the addition of the noise in the telephone frequency band
which can very well cause loss of the modem speed.

To test the theory which is the reason really would be first
to test only the filters in a clear line (with no DSL in it)
and see if they affect the speed at all. If the speed is
lowered also there then the filters are to claim. If those
filters do not affect by itself, then the reason coudl be added
noise because of DSL signals on the same line.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/