Hum from phone wires running next to mains?

[snip]
: : I've seen cables, including CAT5, with both twisting : : _and_ shielding around the whole cable assembly. I : : don't know how much the effectiveness works together. : : I have not had a case where I would consider using it.
That's STP (shielded twisted pair) and is not really worth it for most applications. There is a military spec. for it somewhere, I believe.
It's also a different impedance to UTP so may not work correctly with all equipment.
Ivor
Reply to
Ivor Jones
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All outside plant telephone cable with the exception of the local drop cable is shielded. Inside a telephone office equipment room, T1 and higher speed data cables are all shielded if the cable extends between rows or for more distance in one row than 4 racks.
STP is significantly expensive, and will not commonly be seen anywhere that it is not absolutely required. For example, it would make no sense to use it within a normal customer premise area, unless there is an equipment room with multiple rows of equipment racks.
Reply to
Floyd L. Davidson
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I believe I can help here. Rightpondian "flex" Leftpondian "cord"
Reply to
Graham.
To me, Phil's post illustrates how *similar* the our systems are, and I strongly suspect that the reason why we don't see REN
Reply to
Graham.
It should deal with hum pickup on audio cables quite nicely. However shielded twisted pairs are considerably more expensive, and you have to be careful about generating ground-loops in the shield grounding.
I replaced your non-standard (: :) quote markers with the normal '>'. Please don't use thos non-standard characters. They foul up other software.
Reply to
CBFalconer
... snip about ringer specs on phones and lines ...
In North America again (I don't know about elsewhere) the normal phone uses 3 wires to connect to the two wires of the phone circuit. The yellow wire carries the ring signal. Just disconnect that and the phone won't ring, and the load is zero.
Reply to
CBFalconer
[snip]
: : I replaced your non-standard (: :) quote markers with : : the normal '>'. Please don't use thos non-standard : : characters. They foul up other software.
With respect, and without wishing to start a row, that's *your* problem. I use non-standard quote marks for a purpose. If your system can't cope with that, then it's up to *you* to do something about it. I have been using the quote marks I use for several years and you are the first to complain.
Ivor
Reply to
Ivor Jones
I don't recall any system in North America that put ring voltage on a separate wire. The yellow wire is generally not connected unless one 4-wire cable is used for two separate telephone lines.
In North America the "normal" line uses only 2 wires. The audio signal is applied between the "tip" and the "ring" of a single pair. "Ring Current" and "Loop Current" are also applied between the Tip and the Ring of the same pair.
Commonly used drop cable has four wires: Green is the Tip and Red is the Ring (positive and negative, repectively for the DC loop current), while the Yellow and the Black wires are not used. (Note that the DC voltages used by telephone companies are negative with respect to ground, hence for DC the Tip wire is at ground potential, and the Ring wire has a negative potential. But the Tip is not at ground potential for Ring Current or for the audio signal.)
One configuration often seen includes a second line on the same cable, using Yellow and Black as Tip and Ring.
Historically the Yellow wire was, for a few years, used for a small AC voltage (nominally 6.8 volts) to power a lamp circuit on some telephone set models.
Another historical use had the Yellow wire as a ground for party line service from the old style mechanical switching systems (such as the Step or Stroeger switching systems once used by the Bell System and by Automatic Electric). On those systems the ring current was applied between either Tip or Ring and ground, which was supplied to the telephone set on the Yellow wire.
Reply to
Floyd L. Davidson
Twisting also makes the loop area low (average over a long stretch is nil). Separating them makes a large loop, increasing the size of the antenna.
Reply to
krw
Consider for a bit just how absurd that statement is...
Are you posting your articles for your personal edification, or are they intended to be read by an audience? Who should you format them for, yourself or the audience?
Your non-standard quote characters are *not* appreciated by the audience, and indeed the more sophisticated members that you might want to appeal to the most are the ones most likely to make use of software options based on the quote marks.
What your formatting style does, is tell the reader what your priorities are, and that your ability to comprehend the effect is apparently impaired.
Reply to
Floyd L. Davidson
That is not a valid analysis. It is a transmission line, not an antenna.
Consider that the effect, both for relatively small gauge cables, such as the ubiquitous 26 gauge used today, is *exactly* the same as the effect on the open wire lines used in the 30's and 40's with several inches of separate between a pair of much larger copperclad steel wires. And while the twist on some cable is measured per inch, on typical telephone cable it is measured in many inches per twist, and on those old open wire lines it was in hundreds of yards per twist.
Reply to
Floyd L. Davidson
Well, I said my piece. The normal method of handling it is the casual plonk.
Reply to
CBFalconer
It sure as hell is. Open up the loop and it makes a *wonderful* antenna.
...and open-wire transmission lines won't pick up stray noise?
Reply to
krw
Well, it is possible that my memory is fouled. Haven't needed to disconnect ringers for at least 20 years.
Reply to
CBFalconer
It's a "wonderful" antenna regardless. But it's a single conductor long wire antenna. Changing the spacing is merely changing the effective diameter of the single conductor. To get any other effect requires spacing that is significant in terms of wavelength (greater than perhaps 1/8th of a wavelength, for example).
It picks up as much, or as little, as unshielded twisted pair of smaller gauge and closer spacing. That's the point... there isn't any difference. In either case what you have is a single conductor longwire antenna, not a loop antenna, until the spacing is a significant fraction of a wavelength.
Reply to
Floyd L. Davidson
Plonk
Reply to
Michael A. Terrell
| Ivor J| |> |> With no respect, | | | Plonk
You should do that more often.
Reply to
phil-news-nospam
Non-standard usage can make your posts harder to understand, and more difficult for others. Apparently, you don't care. I'm just adding one more response to let you know that your non-standard usage is not appreciated.
Ed
Reply to
ehsjr
: : : : : Ivor J: : : : : : [snip] : : : : : : : : I replaced your non-standard (: :) quote markers : : : : : with the normal '>'. Please don't use thos : : : : : non-standard characters. They foul up other : : : : : software. : : : : : : With respect, and without wishing to start a row, : : : that's *your* problem. I use non-standard quote marks : : : for a purpose. If your system can't cope with that, : : : then it's up to *you* to do something about it. I : : : have been using the quote marks I use for several : : : years and you are the first to complain. : : : : Consider for a bit just how absurd that statement is...
Which part..? The part where I say I use non-standard quotes for a reason, or the part where I said nobdy has so far complained..?
: : Are you posting your articles for your personal : : edification, or are they intended to be read by an : : audience? Who should you format them for, yourself or : : the audience?
Both.
: : Your non-standard quote characters are *not* appreciated : : by the audience, and indeed the more sophisticated : : members that you might want to appeal to the most are : : the ones most likely to make use of software options : : based on the quote marks.
So why, in my 10+ years of Usenet use, is this the first complaint..?
: : What your formatting style does, is tell the reader what : : your priorities are, and that your ability to comprehend : : the effect is apparently impaired.
Your ability to comprehend my reply appears to be impaired also.
Ivor
Reply to
Ivor Jones
[snip]
: : Non-standard usage can make your posts harder to : : understand, and more difficult for others. Apparently, : : you don't care. I'm just adding one more response to : : let you know that your non-standard usage is not : : appreciated.
Ok, you're the *second* complaint in 10+ years. When that figure gets to a noticable percentage, I might sit up and take notice.
Ivor
: : : : Ed
Reply to
Ivor Jones

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