A Broadband and ADSL forum. BroadbanterBanter

Welcome to BroadbanterBanter.

You are currently viewing as a guest which gives you limited access to view most discussions and other FREE features. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload your own photos and access many other special features. Registration is fast, simple and absolutely free so please, join our community today.

Go Back   Home » BroadbanterBanter forum » Newsgroup Discussions » uk.telecom.broadband (UK broadband)
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

uk.telecom.broadband (UK broadband) (uk.telecom.broadband) Discussion of broadband services, technology and equipment as provided in the UK. Discussions of specific services based on ADSL, cable modems or other broadband technology are also on-topic. Advertising is not allowed.

trying to understand adsl (in the UK)



 
 
Thread Tools Display Modes
  #1  
Old December 23rd 07, 06:54 PM posted to sci.electronics.misc,uk.telecom.broadband
tg
external usenet poster
 
Posts: 82
Default trying to understand adsl (in the UK)

Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard adsl
through a BT line (with filter). It's always worked well so I tested
it on an oscilloscope. When I put the scope probe onto the terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.





  #2  
Old December 23rd 07, 07:40 PM posted to sci.electronics.misc,uk.telecom.broadband
[email protected]
external usenet poster
 
Posts: 735
Default trying to understand adsl (in the UK)



"tg" wrote in message
...
Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard adsl
through a BT line (with filter). It's always worked well so I tested
it on an oscilloscope. When I put the scope probe onto the terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.



You need to look for signals in the 1M+ range.
What you have there is just interference which the ADSL modem has to filter
out.
The actual ADSL signal will be in the millivolts range I would think
(depending on losses).



  #3  
Old December 23rd 07, 09:52 PM posted to sci.electronics.misc,uk.telecom.broadband
Roger Mills
external usenet poster
 
Posts: 368
Default trying to understand adsl (in the UK)

In an earlier contribution to this discussion,
tg wrote:

Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard adsl
through a BT line (with filter). It's always worked well so I tested
it on an oscilloscope. When I put the scope probe onto the terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.


Was the modem cable actually connected to a modem or router, or was it open
circuit. If the latter, there'll be no synch signal, since it takes two to
tango!
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!


  #4  
Old December 23rd 07, 10:07 PM posted to sci.electronics.misc,uk.telecom.broadband
Graham.
external usenet poster
 
Posts: 503
Default trying to understand adsl (in the UK)



"tg" wrote in message
...
Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard adsl
through a BT line (with filter). It's always worked well so I tested
it on an oscilloscope. When I put the scope probe onto the terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.




You have connected the scope directly to the BT line the
unfiltered port on the filter *is* a direct connection to the
line. The line is balanced transmission line for voice (PSTN)
and ADSL, unless you have a scope that is isolated from
mains earth when you connected the probes you would
have earthed one side of the line. Pick up a phone and
listen when the scope is connected and you will probably
hear the result, a deafening mains hum.
Even if you got the RF waveform to display clearly
on the scope it wouldn't be very instructive.
A spectrum analyser would show you the DMT
up and down spectrum
http://www.mauritiustelecom.com/down...rners/ADSL.pdf
and whilst I agree such pretty pictures are instructive, in practice
testing in the analogue domain like this is not used to
test ADSL lines very much outside the R&D labs.

Oh, and I suppose you know that connecting un-approved
equipment is frowned upon in some quarters?


--

Graham

%Profound_observation%


  #5  
Old December 23rd 07, 10:17 PM posted to sci.electronics.misc,uk.telecom.broadband
Graham.
external usenet poster
 
Posts: 503
Default trying to understand adsl (in the UK)



"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
tg wrote:

Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard adsl
through a BT line (with filter). It's always worked well so I tested
it on an oscilloscope. When I put the scope probe onto the terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.


Was the modem cable actually connected to a modem or router, or was it
open circuit. If the latter, there'll be no synch signal, since it takes
two to tango!




Good point, if your local modem is disconnected the DSLAM (the modem
ar the exchange) goes to sleep.

--
Graham

%Profound_observation%


  #6  
Old December 23rd 07, 10:47 PM posted to sci.electronics.misc,uk.telecom.broadband
tg
external usenet poster
 
Posts: 82
Default trying to understand adsl (in the UK)


"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
tg wrote:

Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard
adsl
through a BT line (with filter). It's always worked well so I
tested
it on an oscilloscope. When I put the scope probe onto the
terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with
what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.


Was the modem cable actually connected to a modem or router, or was
it open circuit. If the latter, there'll be no synch signal, since
it takes two to tango!


thanks for your response roger, I didn't know it had to be connected
to a router. I was testing on an open circit, just touching the
terminals on the end of a moden cable with the probe. In response to
what [email protected] said earlier I did a test again this time using a
volt setting of 20mV and a timer setting of 20u secs and I got
several strands of sine wave mixed together but I don't know what this
was.

--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!



  #7  
Old December 23rd 07, 10:49 PM posted to sci.electronics.misc,uk.telecom.broadband
tg
external usenet poster
 
Posts: 82
Default trying to understand adsl (in the UK)


"Graham." wrote in message
...

I'm not getting very far with this. Maybe I'll have to buy one of
those proper ADSL testers that are outrageously expensive....


  #8  
Old December 23rd 07, 11:42 PM posted to sci.electronics.misc,uk.telecom.broadband
The Natural Philosopher
external usenet poster
 
Posts: 1,000
Default trying to understand adsl (in the UK)

tg wrote:
Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard adsl
through a BT line (with filter). It's always worked well so I tested
it on an oscilloscope. When I put the scope probe onto the terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.





go hear and read.

www.kitz.co.uk
  #9  
Old December 23rd 07, 11:46 PM posted to sci.electronics.misc,uk.telecom.broadband
The Natural Philosopher
external usenet poster
 
Posts: 1,000
Default trying to understand adsl (in the UK)

tg wrote:
Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard adsl
through a BT line (with filter). It's always worked well so I tested
it on an oscilloscope. When I put the scope probe onto the terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.



I suggest you learn ti use a scope befre you try and use it to debug ADSL..

Thats mains hum.


No adls signal at all - leastways that's what the 'fur' on the hum is,
probably. If the ADSL was active.

the scope is about he least useful thing to diagnose an ADSL lime there
is. A spectrum analyser at a few thousand would be better, but best of
all is a ADSL router.




  #10  
Old December 24th 07, 12:03 AM posted to sci.electronics.misc,uk.telecom.broadband
m
external usenet poster
 
Posts: 82
Default trying to understand adsl (in the UK)



The Natural Philosopher wrote:
tg wrote:

Hi. I want to understand adsl better so I can diagnose a faulty or
weak signal when I see it. My own broadband at home is standard adsl
through a BT line (with filter). It's always worked well so I tested
it on an oscilloscope. When I put the scope probe onto the terminals
of the RJ11 modem plug here is a picture of what was on my scope.
http://www.zen73857.zen.co.uk/adsl
According to this picture the adsl signal is on a 20millisecond
cycle - which translates to 50Hz - and this doesn't tally up with what
I've read about adsl on the internet, which is 25Kz and up. Was I
getting some interference or leakage from the mains? This pic also
shows AC at about 2.5volts - is that correct for adsl?
Thanks for any help.





go hear and read.

www.kitz.co.uk


In which you will no doubt learn that the ADSL signal is composed of a
varying number of 'BINS' each 4KHz wide. The total number of these
depends on the available reliable bandwidth of your line.
You will never be able to discriminate between these with an ordinary
oscilloscope. It will just look like 'noise' i.e. lots of 'shash'
About the only way to see these without resort to an expensive spectrum
analyser is to use an ADSL modem like a Dreytek Vigor which will display
the amplitude, signal to noise and number of binary 'bits' in each 'BIN'

As a previous poster says, all you were seeing is mains hum.

Mike

 




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
I don't understand that! Harry Bloomfield uk.telecom.broadband (UK broadband) 4 October 28th 07 05:17 PM
Newbie trying to understand Greg uk.telecom.voip (UK VOIP) 3 October 15th 06 01:15 PM
Does any understand this log message please? Steve uk.telecom.broadband (UK broadband) 0 October 15th 05 02:05 PM
Don't understand bandwidth sniper uk.telecom.broadband (UK broadband) 12 August 18th 04 01:52 AM
beginning to understand - I think! Me uk.comp.home-networking (UK home networking) 2 April 11th 04 10:03 PM


All times are GMT +1. The time now is 05:32 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.Content Relevant URLs by vBSEO 2.4.0
Copyright 2004-2020 BroadbanterBanter.
The comments are property of their posters.