Loop Specs & Other Musings 1

[Arr]

Hey all, musings comments invited...

Been fooling with loop start line voltages, loop current and noise problems that have all come my way in the last several months.
Haven't had line noise before like I seem to be getting now. ?? Why? Am I just more aware? Praps.. Remembering that I used to see line voltages at -48.5 to -49.5 when ever I bothered to test... usually when one of those OLD fax machines wouldn't accept a transmission. But lately been seeing line voltages right up at -52 to -52.1 ??

Are the Telcos boosting line voltages accross the board to get better DSL distance? Or is it a change in how they perceive customer equipment... CPE now being the norm instead of the exception... and the Telco is trying to compensate for a bizillion kinds of terminal equipment. ??

Made WHERE??

-52vdc will take loop current right up to 40-50ma on Norstars. Been using two resistors in series (one each leg) to attenuate and ballance the line. Getting results of 25 to 30ma afterwards. Not much voltage drop. ??

So have been googling my head off and found this:

http://www.ospmag.com/index.html

Some senior tech type grey beards are suggesting that I'm shadow boxing and PBX/KSU manufacturers make their gear to allow for the entire range of Continental Telco standards. ??

NOTE: Not sure yet if my interventions have solved noise issues. Too much to line noise to have only one cause... but the voltage thing is bugging me.

PhM

 

[exsmogger]

I don't find that a couple of extra volts makes nearly as much difference as loop current. An ideal level of loop current is in the 25-30ma range. Much more than that and the line will sound "hot" with increasing echo on the line, and increasing chance of damage to electronic components. I'd always recommend putting surge suppressors on both the lines and electrical. I'm pretty sure Mike Sandman has loop current attenuators available for excessive loop current (40ma or higher)on CO lines.

Brian Cox
J & J Communications

http://www.jandjcommunications.com

brian@jandjcommunications.com

 

[Arr]

Brian,
Have looked at the sandman stuff. The two resitors mentioned just act to extend the line ergo lower loop current at the device. I would like to see some Nortel comments about what the LS/DS trunk cards and older KSUs and optimal current loads.
It would seem to me that a difference of .5vdc could drive up the loop current considerably ... gains set too high at the Telco..
Just noodling around to see if there is a root cause to some of this..

Cheers
PhM

 

[PERRYPJ]

-48 TO -52 HAS BEEN A STANDARD FOR YEARS ALSO GOES FOR PABX'S.

OLD ROLMEN WORKING ON NORTELS

 

[Arr]

Perry,
I'm well aware of the standard. But used to see the standard at the low end now see it at the high end. Voltage pushes loop current.

PhM

 

[exsmogger]

On paper an extra .5 volts would increase current by about 1ma. So an increase from 48 to 52 volts would increase current by about 8ma. An increase of this much would definitely be a concern, but getting the local phone company to do anything about it is another matter.

I would assume that the telecom manufacturers take this into account and allow for proper operation of their equipment within a certain range of voltage and current. Of course assuming has gotten me in trouble more than once!

I know on the MICS you can set lines for short, medium or long CO to compensate for high or low levels of line volume. So Nortel does make some allowance in this regard.

Brian Cox
J & J Communications

http://www.jandjcommunications.com

brian@jandjcommunications.com

 

[Arr]

Brian,
Your post is what I generally thought too. The paper calculations don't go in the field because the trunk ports have active components. In field testing, I found that a voltage drop of .02 through the resistors I described placeing created a difference of 15ma, going from 40 to 25. I also found that the fidelity wasn't effected this way either.
You're right about the ICS long/short trunk option, but on the older stuff, of course, it doesn't exist.
So I was hoping someone out there would have an idea why the CO gains would be all turned to the high point... I could have just found every hot circuit in town?

Cheers
PhM

 

[executone]

I asked this question to a SBC Tech. He said that the higher voltages are more common on lines that feed through a slick. The old standard was copper from central office to customer building, but now they go from central office on fiber to network interface, convert to copper, then to customer building.

I have had to request them to adjust some lines, but if they replace the card at the slick that controls that line problem comes back. It is a loosing battle with Telco.

 

[Arr]

Brian,
BINGO! The slick is the thing that I was missing in this picture. We have them installed around in increasing quantities. I know of their existance but forgot to include them in the outside plant mind picture. This just has to be part of the answer as the sites I am having trouble with are at the far end of various fibre trunking/sub trunking.
Thanks.

PhM

 

[executone]

Arr,

Glad I could clarify it for you.

Latter,
Jeff

 

[Arr]

Ah.. Jeff. Yes. Sorry. Got excited.

Still you got my star for that one.

Cheers
PhM