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The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

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Re: [vox-tech] help - dsl
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Re: [vox-tech] help - dsl



On Thu, 26 Oct 2000, Mark Kim wrote:

> On Thu, 26 Oct 2000, Peter Jay Salzman wrote:
> 
> > ok, now for the dumb question.   suppose you had a phone hooked up to a DSL
> > line, with no splitters or filters.  what would you hear?

DSL is a frequency-multiplexing scheme, with voice occupying up to 4kHz,
and data occupying various bands above 20kHz (to 1MHz?).  Some small
signal in the audible range might be noticable, depending on how good your
hearing is (supposedly good human ears can hear up to 22kHz).

> I think you aren't supposed to tell whether a telephone line has a DSL
> activated or not, so I guess you don't hear anything but a dialtone.  I
> think the idea is that you don't have to synchronize the installation of
> the filters with the DSL activation at the central office.

If you plug into the data line, the low-frequency dialtone shouldn't be
audible because is the design of the filter to block it out.

> Pacbell messed up our hookup, 

I thought you were going to do that yourself?

> so we have separated voice and data lines (three wires -- one shared
> between the two).

This should be easy to fix.  I cannot seem to find a schematic of a
splitter, but I would imagine it is something like the following (with
maybe some resistors as well):

       from CO
       |     |
       |     +---------+
       |               |
       +-------------- | ---------------+
       |               |                |
       |               |                |
 +-----+-----+         |           -----+-----
 | inductor  |         |            capacitor
 +-----+-----+         |           -----+-----
       |               |                |
       |      |C|      |  +----------+  |
       +------|a|------+--+ inductor +--+
       |      |p|      |  +----------+  |
       |               |                |
 +-----+-----+         |           -----+-----
 | inductor  |         |            capacitor
 +-----+-----+         |           -----+-----
       |               |                |
       +-----+   +-----+-------+  +-----+
             |   |             |  |
             voice             data
                              (*)

so it sounds like the final "common" (*) to the data connection didn't get
made, which should be straightforward to fix at the splitter.

> When I hook up a telephone
> to the data line, I don't hear anything (unless I have my DSL modem hooked
> up, in which case I hear negotation tones).

You do hear something?  High pitched? Interesting...

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