Interesting experiment with ADSL splitter - Page 1
Forum section: electronics / testgear

author: Jeniffer Chris
author_rank: Newbie
timestamp: November 26, 2013, 05:00:33 pm
content: As we know, the ADSL splitter box has 1 input and 2 outputs, one for phone signal line, and the other for internet signal linePlug the telecommunication line into the input. Then in the output lines, I make the exchange. I plug the phone line to the internet output, and the internet line to the phone outputThen I dial the phone to call to a fax numberSurprisingly, 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 usualSecond experimentI have been considering what happens if I make the feedback from out put to input of a ADSL splitter, as well as change input to output and vice versaBelow are my steps:- Take the first splitter, plug the phone line to the Net output (NOT the input) of it- Plug the input of the first splitter to the input of the second splitter- Plug the Phone output of the second splitter to the phone output of the first one- Plug the Net output of the second splitter to Modem, and connect to laptopSee diagram in my attached screenshotHere I made some abnormal things:- Telephone signal transmits into the output, not the input of the splitterThe output of second splitter is connected back to the first oneSurprisingly, my laptop can access internet normally. Nothing wrong happensWhy my extraordinary actions do not affect the operation of the splitters?

author: AG6QR
author_rank: Frequent Contributor
timestamp: November 26, 2013, 05:30:39 pm
content: A simple ADSL splitter just passes the input straight to the net output, and inserts a low-pass filter between the input and the phone port. The low pass filter has a very high input impedance at the ADSL frequencies, so the utility company's equipment operating at ADSL frequencies doesn't "see" any circuitry connected to the phone port.In your first experiment, when you swapped ports, you connected the phone straight to the phone line. It's now seeing all of the signals on the phone line, including the audio frequencies and the ADSL frequencies. The modem is now hidden behind that low pass filter, so the ADSL frequencies won't reach it. The phone should work perfectly, and the modem won't work. My guess is that you heard a busy signal for the usual reason -- the line was busy at the other end.For your second experiment, note that since the input is connected straight to the net output, the diagram you drew just shows that, as a first approximation, you made a straight through cable. It's not surprising that the ADSL frequencies make it through. What were you expecting to happen?

author: Rigby
author_rank: Super Contributor
timestamp: November 26, 2013, 08:00:17 pm
content: They're not splitters, they're filters. Well, they're splitters AND filters, but they only filter one side after the split.

author: Co6aka
author_rank: Unknown
timestamp: November 26, 2013, 08:40:54 pm
content: In the RF world we call 'em "diplexers." (And there are also "triplexers" and so on.)http://en.wikipedia.org/wiki/DiplexerSee the "Basic technology" section for ideas on frequency response:http://en.wikipedia.org/wiki/Digital_subscriber_lineIn the following article, on page 4, is a DSL spectrum graphic:http://www.alliedtelesis.com/media/pdf/dsl_wp.pdf

author: Jeniffer Chris
author_rank: Newbie
timestamp: November 27, 2013, 05:06:16 pm
content: Quote from: AG6QR on November 26, 2013, 05:30:39 pmNo, for the first experiment, line was not busy. When I set the connection back to normal, I can heare the fax tone. But when I swapped again, I continue to hear busy tone. This is replicated many timesFor the second experiment, by looping the output back to input, I expect to have a disorder manner in the way the splitter worked. But it did not happen.There is suggestion that to create a feedback loop I would have to cut into the cables and splice the red to the green and other green to the other red. But this action is very difficult to accomplish in actual, since it requires me to be very skillful

author: Jeniffer Chris
author_rank: Newbie
timestamp: December 04, 2013, 06:23:13 pm
content: I just made the third experiment by cutting into the cable, and connect the wire red by red, green by green. Thanks to God, no blow up happens.See my attached screenshot for more detailIn a), I loop the net output to input, and connect phone output to a telephone machine. No signal at allIn b), I loop the phone output to input, and connect net output to a modem, this time I can access internet normallyIs it working correctly?