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Central office lines

Started by Phonesrfun, March 30, 2010, 06:28:28 PM

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Phonesrfun

In a previous post in another thread, Donna, (Bwanna) said:

Quote
we are getting a little off the topic of dan's amazing find. but to the subject of equalizers i would like to add that loads coils are installed in the plant now. simply put these are amplifiers placed at 6k intervals on loops >18k.
not sure when these came into use. but load coils ensure signal is as strong 8 miles away from the CO as it would be next door to the CO. so i am thinking once load coils were in use, the equalizer was no longer necessary  also due to this amplification, i think a 302 would sound just fine regardless of loop length.

http://tinyurl.com/ygq39yf


So as to not hyjack D/P's trial 500 thread any farther, I thought I would start a new thread on transmission lines.

Donna, I don't disagree with what you are saying, in fact you deal with line lengths every day.

The basics still apply, and the reasons for the development of the equalizer are based on the long loops and short loops thing.

I do think that this could be a very interesting topic.  I have some thoughts and questions about present-day lines, but I am at work right now so I will ask them later on tonight when I get home.
-Bill G

bwanna

good idea, bill to move this topic. i probably should have started a new topic w/my post. :-[
donna

Phonesrfun

-Bill G

gpo706

GPO 706's had a regulator board which could be put in and out of circuit by removing, turning upside down and re-inserting it.

http://www.britishtelephones.com/t706.htm

AUTOMATIC SENSITIVITY REGULATOR
Regulator No. 1 consists of a small printed wiring board on which are mounted a Resistor, Bulb, No. 15, Rectifier-element No. 209 and two carbon resistors of 15 and 47 ohms connected as shown on Dgm N 801. These components are soldered directly into the printed wiring pattern which is connected to the telephone circuit by five plug points formed on one end of the board. Three more plug points, which are strapped together, are provided at the other end of the board so that reversal of the regulator board in its jack will remove it electrically from the telephone circuit. All the printed wiring plug terminations axe coated with a thin layer of solder to provide good contact with the jack springs when the regulator is plugged in.
"now this should take five minutes, where's me screwdriver went now..?"

gpo706

BTW seems I'm 1008m from the exchange, weird it still called by its old exchange name "DONALDSON".

http://www.samknows.com/broadband/exchange/ESDON
"now this should take five minutes, where's me screwdriver went now..?"

rp2813

Thanks Bill, as I didn't intend to hijack such an important thread as D/P's.

I don't notice much difference in volume between my equalized 500 and a 302 when using either type at home.  If anything, the 302 may not have quite the same amount of volume as my 500's.  When I recently acquired my 5302, I noticed that the volume was noticeably lower than the 500 it replaced, although it got better when I adjusted the positioning of the receiver end against my ear.  Perhaps this has do do with the HA1 existing inside a G-shaped receiver cap.

While I'm at the edge of my switch's serving area, the CO is actually less than two miles away.  Basically the switch is located downtown, I'm on the fringes of that district, but it also serves areas way to the south, much further away than I am.  So although I'm at the border between "Main" and "Axminster" exchanges, there are other "Main" subscribers who are much further from the switch than I am.  If I dial two out of the four adjacent neighbors, I'll be going through the Axminster switch to reach them, which is probably a couple of miles away from me in the other direction from Main.  I'm sure none of my neighbors who are served out of Axminster even realize that their dialtone is coming out of the next town over.

It sounds like I have little to worry about regarding my equalizer since there are load coils in play these days, but this is still an interesting discussion, and it does raise the question about 302's having worked better for outlying customers than the early 500's.   It seems the opposite is actually true based on what I've read here.
Ralph

Phonesrfun

The 500's were supposed to be much better than the 300's on long loops.  I have seen a chart and some discussion of that before.

What have you seen that would show the opposite?  I am curious.
-Bill G

bwanna

bill, wasn't the whole reason for the development of the 500sets to accommodate rural customers. in other words, longer loop lengths? to put in in layman terms the equalizer basically lowered the juice on shorter loops?

ralph at 2miles, loads would not be necessary. placement is usually >18k... the first load at 3k, subsequent loads at 6k intervals.

donna

Phonesrfun

Quote from: bwanna on March 30, 2010, 09:04:33 PM
bill, wasn't the whole reason for the development of the 500sets to accommodate rural customers. in other words, longer loop lengths? to put in in layman terms the equalizer basically lowered the juice on shorter loops?

ralph at 2miles, loads would not be necessary. placement is usually >18k... the first load at 3k, subsequent loads at 6k intervals.



From the reading I have done, I would say a great deal of the reason was for the rural customers, yes.  For sure the part about getting 5dB more gain out of each of the transmitter and the receiver.  Seems they were also pretty proud of the prospect of lower maintenace costs and a more versitile phone that was more configurable.  The 300 series probably had 10 or 15 slightly different models and the 500 had different models but fewer. 
-Bill G

rp2813

It's been a while, but I recall reading somewhere about the 5302's development and I'm guessing it was just someone's opinion.  It's entirely backwards from what makes sense.  If I remember correctly, not only did the writer state that the 302's were better on long loops, but that the 5302 was developed in order to provide the newer style phone to rural customers that were stuck with 302's, seeing as how the 500 didn't do as well on long loops.  I don't remember where I read this, but it runs contrary to everything I've read about the 500's development, and I think Bwanna will agree with me that the Phone Company wouldn't go out of its way to develop station equipment based on rural customer demands.  The cost of providing  and maintaining service to rural customers is a lot more expensive from a ROI perspective than it is for urbanized areas.  If I can track down the site where I read this, I'll provide a link.
Ralph

McHeath

Yes Ralph I've read this theory as well, and I can't recall where either.  It does not make much sense does it?

GPO706 that's a handy little web site that shows the distance from the CO.  Wonder if such a site exists for here in America?

Phonesrfun

Quote from: gpo706 on March 30, 2010, 07:03:03 PM
GPO 706's had a regulator board which could be put in and out of circuit by removing, turning upside down and re-inserting it.

http://www.britishtelephones.com/t706.htm

AUTOMATIC SENSITIVITY REGULATOR
Regulator No. 1 consists of a small printed wiring board on which are mounted a Resistor, Bulb, No. 15, Rectifier-element No. 209 and two carbon resistors of 15 and 47 ohms connected as shown on Dgm N 801. These components are soldered directly into the printed wiring pattern which is connected to the telephone circuit by five plug points formed on one end of the board. Three more plug points, which are strapped together, are provided at the other end of the board so that reversal of the regulator board in its jack will remove it electrically from the telephone circuit. All the printed wiring plug terminations axe coated with a thin layer of solder to provide good contact with the jack springs when the regulator is plugged in.

Scot:

That is interesting about the regulator board.  When was it introduced?
-Bill G

Phonesrfun

So, earlier today, I was sitting at my desk at work and had some questions to ask about central office lines.  I have done a bunch of reading about transmission lines and loading coils and carrier systems of the days of old.  However, some of the things about todays CO lines are kind of a mystery to me.  Granted, the pair of wires that comes into the house as a "copper" pair is probably going to go by the wayside some day, and it may even be happening right before our very eyes.  For instance, there is FiOS and other fiber optic based systems and VoIP and so forth.  Currently, I use Vonage, so I don't even have a line connected to the phone company.  It comes in through my cable and comes into a router, which I like to think of as a Central office in a box, because it supplies the battery and some of the supervisory functions that a CO would provide.

But, going back to that which the traditional telcos provide, I seem to have a belief that most "copper" that comes to a residence is actually only the "last mile" of wire.  I think that coming from the CO, there could be fiber backbones and/or T-1 circuits that are all basically data.  Then these go into some cabinets at the neighborhood level, and are broken out as copper pairs to make it to the house.  Therefore the term the "last mile".

If that is generally the case, then it would stand to reason that these roadside cabinets would have to provide the DC power and the ringing current as the signal was converted from data to an actual DC loop.

And, if that's the case, then the average loop these days would be much shorter than in the days when the copper pair ran all the way from the subscriber to the central office as its only path.

I would really like to know how this actually works these days.  I also fear that there is no one answer, because like anything else these days, it probably gets really convoluted.

I know this is probably a technical question that perhaps only a few understand, let alone answer.  Bear with me, 'cause I don't want to kill this thread with too much detailed information that nobody else cares about.

Cheers, and I promise the next question I ask will be so simple, even a cave man can answer.  (To borrow a phrase)

-Bill G

bwanna

ralph, i am reading in ralph o meyer's- old-time telephones,  pgs 78-79.  in brief describes using a local battery w/ a 307 set on long common battery lines. due to the resistance on the long loop, direct current was too small to produce a strong voice signal.  this produced a signal nearly 2x that of the common battery 302.
in regard to the 5302's. what i remember reading is that they were developed to use up remaining 302 bodies. also to provide the more modern look to subscriber's still using the 302.
i agree that Bell would not go out of it's way to satisfy rural customer's needs. that statement is still true today. i would guess until post WWII, telephone lines did not even run to more remote locations. as demand grew & technology developed, the infrastructure was expanded. what i gather from my reading is the 500set was designed so that the local battery would not be needed on the longer loops.

 
donna

bwanna

bill, to address your comments on CO lines. firstly there are still many many copper loops from CO to prem.  almost 100% of the lines with in 2-3 miles of a CO are copper. the fiber & T1 loops you describe are known as pair gain systems.
i am not sure on the timeline of these developments. as the population in more remote areas began to grow, the phone company looked for more economic ways to provide service.
the oldest pair gain system that i am familiar with is fed by copper T1. a T1 line provides 24 data channels. thus 24 pots lines can travel on one copper pair. this is accomplished by converting the analog signal from the switch to a digital signal. this signal leaves the CO on the T1 & travels to a remote terminal where the signal is converted back to analog. from the RT copper pairs run to the neighborhood cross connect boxes. at the the x-box the CO pair is connected to the individual distribution pair to the customer's prem.
as time went on the remote terminals began to be fed by fiber.
the phone company very seldom will upgrade copper loops to pair gain. so in the older areas you will still have copper. some of the newer x-boxes will be 100% pair gain pairs. a x-box that is any distance from the CO will most likely contain a combination of copper/pair gain loops.
this covers POTS lines.

early in this decade, ADSL (hi speed internet) service became the hot item. initially telco was only able to provide DSL over a copper pair. the max distance the data can travel is 17.5k. so a pair gain system incorporating DSL came to  be. the data signal originates in an RT, then is distributed via copper to the subscriber. the POTS service still comes from the CO & is connected to the data signal in the RT so that both signals travel to the subscriber on the same copper pair.

then about 3yrs ago we move up to video services. it's the same method of distribution for video signal as the pair gain ADSL signal.

of course telco's are only going to invest where they will get bang for their buck. many sparsely populated areas do not have ADSL or video service. most cable companies do not have infrastructure in these areas at all. so the only means of home telephone service is CO based POTS.

my knowledge comes from 10yrs of work in the field in michigan. some of this may differ in other regions & someone with more experience than myself could surely explain in more detail.
sorry if i rambled. have been off work nearly a month w/back trouble. so i am kind of "jonesing" for telco talk :) thanks for indulging me.
donna