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thinhnghiem

join:2014-01-29

Interesting experiments with ADSL splitter

As we know, the ADSL splitter box has 1 input and 2 outputs, one for phone signal line, and the other for internet signal line
I have executed many experiments with this device, and some give out interesting results. I list here 5 of them. Their schemas can be found in the attached screenshot
Experiment a)
Plug the telecommunication line into the input. Then in the output lines, I make the swapping. I plug the phone line to the internet output, and the internet line to the phone output
Then I dial the phone to call to a fax number
Surprisingly, I heard the busy tone, instead of fax tone.
Note: When I connect in normal way, plug the phone line to the phone output, and internet line to the internet output, this effect does not happen. That means I heard the fax tone as usual
Experiment b)
I make the looping back from the net output to the input. To do this, I cut into the cable and heal the wire inside, with the same color correspondingly (green to green, red to red)
Then, I connect phone output to a telephone machine.
Result: No tone heard when I picked up the phone machine

Experiment c)
I make the connection between phone output and net output, by cutting into the cable and healing the wire inside, with the same color correspondingly (green to green, red to red), similarity as I did in experiment b)
Then, I connect phone output to a telephone machine.
Result: No tone heard when I picked up the phone machine

Experiment d)
Wall line is plugged into the net output (Not the input). Then, I make the looping back from the phone output to the input. To do this, I cut into the cable and heal the wire inside, with the reverse color correspondingly (green to red, red to green)
Then, I connect input line to a telephone machine.
Result: No tone heard when I picked up the phone machine
Note: If I repeat the same experiment by healing the wire with the same color correspondingly (green to green, red to red), no issue happens. The tone can be heard from the phone machine
Experiment e)
Wall line is plugged into the phone output (Not the input). Then, I make the looping back from the net output to the input. To do this, I cut into the cable and heal the wire inside, with the same color correspondingly (green to green, red to red)
Then, I connect input line to a modem to emit Internet signal
Result: No internet signal is created


pike
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join:2001-02-01
Washington, DC
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Okie dokie.


whocares256

join:2002-03-10
Anna, TX
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1 edit
reply to thinhnghiem

You can swap the dsl modem side of the filter with with the wall input side of the filter and you will be ok. If you do any loop back connection between the phone side of the filter and the wall or dsl modem side of the filter then you will not have a filtered side for the phone.

As far as getting a busy signal you may have reversed the polarity of your line (some older devices do not work with reverse polarity) or created a dead short with the loopback in examples c through e. I have a filter plugged into my dsl modem and then a line going from the wall to the dsl modem side of the filter and then a line going from the phone side to my fax machine and it works fine. Can post pictures if needed.

Edit: What is the model of the DSL filters that you are using? I have F0313DG and a SP-201 dsl splitters that came with my TP-Link DSL modems an I have a couple of LFT4-1 dsl filters that came with my ATT DSL Line and several Corning phone filters that go with my CO-OP dsl line.



tschmidt
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reply to thinhnghiem

What is it you are trying to figure out?

An internet splitter passes phone line directly to the DSL modem and through a low pass filter to the phone. Agree with whocares256 See Profile busy probably caused by swapping the Tip and Ring leads when you looped data back.

The purpose of a splitter or inline filter is to prevent high frequency DSL tones from interfering with voice phone equipment. Splitters typically implement a better filter and you don't need one at each phone so they are preferred. Some splitters implement secondary over voltage protection reducing potential damage from nearby Lightning strikes.

/tom


thinhnghiem

join:2014-01-29
reply to whocares256

Yes, if I connect the phone side to fax machine, it works well

The surprise is that when I swapped the lines, to connect net line to phone machine, and dial a fax number, it results in busy tone

Second, the effect of no tone is heard in b, c, and d is hard to be explained. Why is the tone destroyed in these cases?


thinhnghiem

join:2014-01-29
reply to tschmidt

I do not try to figure out any hypothesis

I did these experiments originally by curiosity. Then, since they result in surprising result, I expect they can be helpful in new discovery in technical


lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1

2 recommendations

Click for full size
Almost all ADSL filters make a direct connection between LINE and MODEM ports. A few have resettable fuse in that path, but that is also equivalent to straight connection.

Of course, there is a low pass filter from LINE to PHONE so you don't literally hear your modem.