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dmxrob6
Premium
join:2005-06-24
Boonville, MO
Reviews:
·AT&T Southwest

SNR drops when internal telephone wiring disconnected?

This makes no sense to me. I've been trying to track down an issue for over a year. This new "clue" has me baffled. Has anyone ever seen anything like this before?

This morning I went to the NID and disconnected the internal telephone wiring but left the home run in-tact (it's one of those jacks that has the slides where you just push down on the tab you want to disconnect).

My SNR for my DOWNLOAD rate will not go above 6.0db now. It will try to get a little higher but it will usually stay right at 6.0db. If it does go higher (I saw it jump for about 5 seconds to 10.0db) it will almost immediately lose frame/signal and disconnect. However, the moment I re-connect the internal telephone wiring everything is fine and dandy and my SNR jumps back up to about 14.5db


d_l
Barsoom
Premium,MVM
join:2002-12-08
Reno, NV
kudos:7
Do you have DSL over POTS or dry loop DSL?


dmxrob6
Premium
join:2005-06-24
Boonville, MO
DSL over pots.


d_l
Barsoom
Premium,MVM
join:2002-12-08
Reno, NV
kudos:7
reply to dmxrob6
This is a guess, but perhaps your phone is leaking current even when on hook. The leakage would be acting as a sealing current to improve attenuation.

Your attenuation would be have to be changing dramatically (about 8 dB) between the phone connected state and the disconnected state to be able to alter your SNR that much. I don't think I've ever seen that much attenuation change with off hook current.
--
TCE Weather


dmxrob6
Premium
join:2005-06-24
Boonville, MO
Reviews:
·AT&T Southwest
The attentuation change was about 0.5db, if that... very minimal.

The last time I spoke to someone at AT&T (about two weeks ago) she said my account showed "Dry Loops DSL" (this is actually U-Verse IPDSLAM ADSL2+) and I assured he we had home phone service. She said that could be causing the issue and was going to have them switch something over. I have no idea if that was ever done or not.


dmxrob6
Premium
join:2005-06-24
Boonville, MO
reply to d_l
BTW, how could I check for leaking current? Is that something I could use a multimeter to detect?


d_l
Barsoom
Premium,MVM
join:2002-12-08
Reno, NV
kudos:7
reply to dmxrob6
I really didn't think that was the problem. It was more a hypothetical guess.

Have you ever tested the stats with the phone wiring connected, BUT no phone in the jack? If that passes muster, do you have a different phone to test in the jack? Maybe borrow one for a stats test?
--
TCE Weather


dmxrob6
Premium
join:2005-06-24
Boonville, MO
Reviews:
·AT&T Southwest
Yes, I've tested it in every possible combination.

If this offers any clue --

With internal wiring DISCONNECTED:

Rx Tx
140 Current Rate 8942 1023
141 Previous Rate 0 0
142 DSL Max Rate 9564 1108
144 Current ATTN DR 8960 1149
145 Current SNRM 6.0 8.0
146 Current LATN 34.6 21.2
147 Current SATN - -
148 Current TP 18.6 12.0

With internal wiring CONNECTED:

Rx Tx
140 Current Rate 11996 1023
141 Previous Rate 0 0
142 DSL Max Rate 12728 1108
144 Current ATTN DR 15132 1160
145 Current SNRM 13.0 8.2
146 Current LATN 34.6 20.8
147 Current SATN - -
148 Current TP 18.9 12.0


d_l
Barsoom
Premium,MVM
join:2002-12-08
Reno, NV
kudos:7
reply to dmxrob6
That is interesting; however, you have ADSL2+ and it may have some unfamiliar quirks.

It seems as though disconnecting the wiring drops your DL max to just about those of ADSL levels. I have no explanation.
--
TCE Weather

public

join:2002-01-19
Santa Clara, CA
reply to dmxrob6
said by dmxrob6:

This makes no sense to me. I've been trying to track down an issue for over a year. This new "clue" has me baffled. Has anyone ever seen anything like this before?

At 10MHz 1/4 wave is 7.5 meters. It is possible that the stub is tuning out some reactance of the incoming line.


dmxrob6
Premium
join:2005-06-24
Boonville, MO
Reviews:
·AT&T Southwest
said by public:

said by dmxrob6:

This makes no sense to me. I've been trying to track down an issue for over a year. This new "clue" has me baffled. Has anyone ever seen anything like this before?

At 10MHz 1/4 wave is 7.5 meters. It is possible that the stub is tuning out some reactance of the incoming line.

I'm afraid you've lost me on that one. Is there a less technical way to explain it?


jimkyle
Btrieve Guy
Premium
join:2002-10-20
Oklahoma City, OK
kudos:2
Reviews:
·AT&T Southwest
said by dmxrob6:

I'm afraid you've lost me on that one. Is there a less technical way to explain it?

I'll give it a try, as a one-time VHF ham operator (K5JKX from 1957 to 1967) and long-time technical writer.

One of the more magical things about high-frequency signals is that otherwise ordinary chunks of transmission line (such as coax or even Cat5 twisted pair) can act as filters and totally trap signals of just the right frequency from getting past the point at which they tap onto another transmission line. At one time we made use of this property to trap out unwanted spurious signals from our ham stations that were making their way into neighbors' TV sets.

That strange property of such lines is part of what makes "bridge taps" such a problem for DSL users; they trap out parts of the DSL signal and make it effectively too weak to be reliably usable.

However for signals at frequencies slightly removed from the critical one that gets trapped, such a "bridge tap" (the internal phone wiring in this case) can actually compensate for other problems on the circuit, and cancel those problems out.

That cancellation effect is what "public" was talking about. It doesn't seem to happen very often, and in any case is usually more of a theoretical condition than one that's large enough to be noticed -- but it might be what's causing your strange situation...

Did this help any? I've simplified the explanation greatly, but I think it still covers the essential part of things...
--
Jim Kyle


d_l
Barsoom
Premium,MVM
join:2002-12-08
Reno, NV
kudos:7
reply to dmxrob6
Do you have a splitter at your NID?

Disconnecting the POTS wire at a splitter shouldn't affect the DSL signal, but with no splitter at the NID, the DSL signal might be improved with the POTS wire stub attached as public See Profile and jimkyle See Profile suggested.
--
TCE Weather


dmxrob6
Premium
join:2005-06-24
Boonville, MO
Reviews:
·AT&T Southwest
said by d_l:

Do you have a splitter at your NID?

Disconnecting the POTS wire at a splitter shouldn't affect the DSL signal, but with no splitter at the NID, the DSL signal might be improved with the POTS wire stub attached as public See Profile and jimkyle See Profile suggested.

Yes there is a whole-house splitter. If I disconnect the internal wiring, the whole house splitter is no longer being used.


djrobx
Premium
join:2000-05-31
Valencia, CA
kudos:2
Reviews:
·Time Warner Cable
·VOIPO
reply to dmxrob6

Yes there is a whole-house splitter. If I disconnect the internal wiring, the whole house splitter is no longer being used.

No longer being used, or no longer connected?

You could either disconnect the filter from the line, or disconnect the house from the filter. I'd test both ways and see what the results are.
--
AT&T U-Hearse - RIP Unlimited Internet 1995-2011
Rethink Billable.