atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring Cat 3 vs. Cat 5e for Voice

Nice guy, Jeff. Keep up the good work.

And, yes, in the old days private held exchanges did as they wished, including using a barbed wire fence as the return on circuits, or in lieu of a grounded talk circuit.

If you are ever lost in Kansas, behind the Eisenhower Museum is the Ford County Museum and the Independent Telephony Museum. They also have the Greyhound Hall of Fame. All just off I-70 about 3 hours west of Kansas City at Abilene.

(How's that for advertising ?)

I once used an entire metal building for one "side" of a station out of a Comdial system.

The customer did not want new cables installed so I was forced to work with what was there from many years before. (I worked for another company back then so the only choice I had was to quit or do the job the way the boss said to) Anyway, it was getting late on a Friday night and I had been at the job site since 5 AM. and this was the last station to be installed. We had maxed out the cable pairs by adding a few stations where there were none before.

The run was around 400 feet and there was no way in hell I was gonna stay and run it that night but I knew the phone had to be working by the next morning so I used the metal building for the white/blue side of the circuit.

I could hear a little bit of static but the customer didn't seem to notice it. I was going to go back and run a new cable but I never got a round to it before I quit that job.

I know this was not the right way of doing things, the point I'm trying to make is that voice signal is very forgiving like so many of you have said.

I'll bet I'm not the only one that has used this method.

I just like the sound of running two phone lines on quad.

Make the length (of the quad cable) long enough and you get a free conference feature!

POTS lines are balanced 600 ohm line, and using a tighter twist will indeed have better rejection to common mode interference and cross talk from other adjacent pairs. It will not however improve the audio quality aside from reducing potential hum, RF interference and adjacent pair crosstalk. Is it worth the extra cost? depends on who is doing the cabling. It's easier to tell an electrician to put four runs of cat 5 to each box than mixing cat 3 and 5 and finding out later he screwed it up. Look up Common mode rejection ratio (CMRR) pertaining to audio lines on the net and you'll find a plethora of info; after all, a telephone line is just a long balanced audio line.
[URL=https://en.wikipedia.org/wiki/Common-mode_rejection_ratio][/URL]

Regarding audio quality of a phone line, the telephone is the most limiting factor. In fact when I have done remote broadcast feeds via phone line, the audio quality can actually be pretty good if you drive it with a good quality transformer at +4db.

No harm in running cat5 aside from difference in cost. It sure beats the old Z-wire with parallel conductors.

I am an electronics technician, and deal with these kind of issues all the time in broadcast studios and recording studios, where noise must be kept to a minimum on all lines. Same theory applies to a phone lines.

POTS lines are balanced 600 ohm line, and using a tighter twist will indeed have better rejection to common mode interference and cross talk from other adjacent pairs.

True but you have to consider the levels in the balanced line. If you are talking about a low level mic line then, yes cable construction is an important consideration because even small amounts of interference will get into the audio.

With a POTS line the level is much higher and the subscriber equipment is basically passive so the line can tolerate a much higher level of interference before it becomes objectionable. The most usual cause of hum and noise on a POTS line is from an unbalanced condition.

The additional twists present in a CAT 5 and higher wire will make no difference to POTS performance. That it would be beneficial goes against nearly a century of telephone engineering. It's always been easy enough to make a wire with the same twist characteristics as CAT5. If there was some advantage don't you think it would have been put into use many years ago?

It's easier to tell an electrician to put four runs of cat 5 to each box than mixing cat 3 and 5

:rofl: The chances of some sparkies getting it right would have nothing to do with me telling them how to do it, even if I were standing there. Besides, they are not the ones doing the termination.

-Hal

I partially agree with you, but the phone company has always juggled "good enough" and costs. Thats why we have a voice bandwidth of less than 4khz, it's good enough. Phone lines run in a tray with other data lines, speaker lines, Low voltage control cables etc. can certainly benefit from every bit of noise rejection possible. 40 years ago and earlier, these weren't so much of a concern because there wasn't all the added noise generating sources in the average building. It doesn't seem too many years back that the telco decided Z wire with parallel conductors maybe wasn't the best thing to wire a building with for exactly the reasons cited above, but thousands of miles of the stuff was still installed until someone woke up and decided twisted pair offered better noise rejection.

Thats why we have a voice bandwidth of less than 4khz, it's good enough.

Yeah and what do we have now with cell phones and VoIP? Voice quality doesn't even come close to that and people have been brainwashed into liking it!

It doesn't seem too many years back that the telco decided Z wire with parallel conductors maybe wasn't the best thing to wire a building with...

Quad or JK wire was fine in the days of one line installations. But the proliferation of two and more lines even in residential required twisted pairs, not for noise rejection but for crosstalk rejection. This is nothing new.

-Hal

My understanding about Quad or JK wire is that it was designed to look nice (it's perfectly round) in baseboard exposed applications at the expense of crosstalk rejection.

For prewired installations, where the wire is is not exposed, twisted pair is supposed to be used. I know of houses built in the mid-60s that were prewired by Bell with 6-pair cable. Even back then they knew that people might want an additional line.

Of course all of this went out the window after deregulation and Bell stopped doing the prewiring. Then most everyone used Quad or JK for prewires until the mid 90s.

As for here, this area was an independent (Contel) and they always used quad for prewires as far as I've seen.

Bell with 6 pair was cat 3.... better than JK and it was used around 1967 and then on. General cable or texarcana made this stuff for years.

My understanding about Quad or JK wire is that it was designed to look nice (it's perfectly round) in baseboard exposed applications...

I'm actually holding a sample of 2 pair cat3 inside wire in my teeth as I type this. Made by General Cable and it's perfectly round.

Wish I could get more of it. Seems it was made for the BOC's.

-Hal