Recently, at a Radio Shack store at the telephone accessories section, I noticed that telephone extension cords were available in lengths up to 25 feet (but I didn't notice any that were longer). Is that because 25 feet is the longest you can go before there's a significant loss of signal strength?
And what about people who access the internet via 56K dial-up? For them, how long can the extension cord be and still have "clean" transmission for error-free downloads?
18,000 ft?
A phone cord is just more wire that connects to the phone company's wire that travels miles to get to your house. So you can make a cord about as long as you want.
The technical details alter a bit, in that the typical phone cord (and a lot of home wiring) is straight conductors (i.e. side by side) but the cable outside tends to have pairs twisted together. The twists in the pairs of wire helps to block some interference (that is why computer cables have much tighter twists, too).
A 56K modem can also work for a very long distance, again, interference can creep in, and that may slow the signal down. There are many other issues that will affect the modems too, so that they rarely get real 56K speed.
Office type phone systems have more restrictions on the length of wire because those types of phones are doing more things and using more voltage that your average "single line telephone".
Charles
18K feet is the limit for certain data transmission technologies (DSL, ISDN, etc), phone wires can be almost arbitrarily long.
That said, I've had better luck with high-quality cables (Cat-5 cable back to the demarc) for 56K dialups, though a lot of that is dependent on the quality of the modem.
If you are stuck with dialup, you might get better results with an external modem, though of course they come in a wide range as well.
You need to shop at Home Depot or Lowe's where you can get 50 foot or
100 ft modular extension cords. When I was renting a room there was no wiring for phone and I used one of these 100 foot extensions to go directly into the network interface box and I was using DSL!- -
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"56k" modems are limited by law to 53k, and seldom get that even that high.
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That's not necessarily true. Some PBXes use the same 48V as the central office, some use less - only 24V. Some use in-band signaling so they don't need any better wiring than the regular POTS telephone. The system I work on is digital, so it has a restriction of 2000 feet, but that's not necessarily true for other PBXes.
One thing you might want to consider is that running phone lines greater than 25 feet is that they get trampled on, tripped over, and get in the way of other things. Radio Shack doesn't sell longer cords because there is little demand for them, and they sell only high demand, high volume stuff. You can buy flat 'silver satin' modular cable in lengths up to 1000 feet or more, and make your own with the crimp-on connectors. I regularly make up custom lengths from 2 inches to a hundred feet or more. But it's risky having things on the floor that people might trip over.
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However, the one thing to be careful of with long extension cords is that they must be *twisted* *pair* cable.
Such extension cords are also commonly available in what is called "flat satin" type cable, which has parallel conductors that are not twisted. That might work if the extension is used with a telephone, but it should be avoided for data, whether it is a DSL or a v.90 modem.
I wouldn't use anything longer than about 6 feet of flat satin cable to a modem.
-- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Not even close. Ma did a loop plant survey back in the 1970's and one operating company reported a 100,000 ft loop....
-- A host is a host from coast to coast.................wb8foz@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433
Old telephone lines that came out of a central office had no electronic equipment to help them out, so a dwelling that was, say, 5 miles (26,400 feet) out of town had to have loading coils on the line every 6k feet. People don't realize it, but there are still a lot of those lines in use, even in cities and towns.
If a phone line has loading coils on it, then it can't be used for DSL at any length. The loading coils have to be removed.
That's 'only' 19 miles. If two cities were farther apart than that, then they would use inter office trunks that were longer than that. Of course, later, it was cheaper to use carrier or pair gain equipment than to put more copper in the ground. So later you saw a lot of T1 circuits, which have repeaters every 6k feet. Then came fiber optic cable and everything changed.
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Found this one: 16 miles, back then longest in Calif. Another website says longest in the world, which might have been possible in 1882, but I'd say state is a safer bet.
writes:
Interesting. Do you know if they had to use the more electrically shielded pairs in the center of the cable to get any sort of distance or was any old pair that the rats hadn't chewed on too much good enough?
-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/
Microsoft Vista - because "Virus Installer" was too long.
That's not necessarily true either. PBXs with analog ports typically use "class A" port equipment, giving them a range of about 200 Ohms as I recall. A class C PBX port (used for off-premises stations) looks very similar to a CO POTS line interface which will reach to about 1800 Ohms.
writes:
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Standard telephone cable back in the '70s was pulp insulated, and for that long, it would have to have loading coils every 6kFt. Or if the line was installed decades before that, they might have had special loading coils.
But this is not to say that it couldn't be something else. In order to get service to farms, some telcos used fenceposts to support the insulators, and strung something like 10 gauge copperweld wire along the fenceposts. Or if it was to a location where they didn't want to build a CO out in the boondocks, they may have used some kind of remote station to serve a small community. It's funny, but the droids back in the service centers still think that a line is copper, even tho it's mostly over pair gain such as fiber. Well, I guess you could blame it on their test equipment, which probably can't tell the diff. :-O
writes:
In Nevada we had a long line with carrier equipment part way (30 miles) and then 15 miles of Open Wire. The OW was ( I think) number 12 copper weld. We also had a circuit of ten mile single wire with ground return . So, not all circuits were on cable.
Oh for the good old days.
Bill K7NOM
Getting a bit far from the original question. Right on. In this province of Canada we used "open wire" even for some subscriber loops in rural areas. Typically it was Number 8 hard copper, each pair spaced 12 inches, on ten pin crossarms. Stories abound about long, long lines with up to, or more than, 100 phone customers on one pair across farming areas of the Canadian prairies and western USA! If anybody had an emergency (such as barn fire) others on the line would respond to a general ring. Copperweld was/is copper coated steel wire. Just looking up Number 8 solid copper wire; noted it has a resistance of approx. 3.3 ohms per mile; so that is 6.6 ohms per 'Loop" mile. Assuming that a typical dial office loop could be around 1000 to 1200 ohms, that's a theoretical subscriber loop distance of, say 174 miles! And with those old fashioned carbon granule microphones, powered local by two 1.5 volt cells, with quite a high output without any tubes or transistors it would probably work quite well, despite the transmission loss over that distance. And anyway some other party listening on that multiparty line could repeat the message down the line! I know we had one such line with 14 customers, each paying 1.75 per month which included the telephone directory and new local batteries whenever needed. Terry Trouble with those rural lines was that they were usually joint use with power lines. resulting in all kinds of induction hum, atmospheric noise pickup and various power switching transients. PS. I think I've seen 50 foot 'extensions' in a local dollar store.
Anything over a few hundred yards and you probably ought to think about things like lightning protection -- not your typical "telephone extension cord."
-- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form che...@prodigy.net.
The 25' cable is probably what best fits on the sales display hook! Sure there are in-line couplers so the sky is the limit for length. For a long cable run rather than having the cable strewn about, why not use standard quad station cable, connect it to one jack, fish, staple or otherwise make a neat job and run to the other jack. Even if you live in a rental, it can easily be done. Remember there is space between the wall-to-wall carpet and the baseboard. Many a low voltage wire has been tucked in there to get around a room unseen.
Before my laptop died, I had a 100' Home Depot MEC that I'd cut the RJ-11s off and put on RJ-45s, and had TCP/IP from the LAN to my Motor Home. :-)
Cheers! Rich
If the limit were 25 feet, you would have a problem connecting your phone to the telco which may be several miles away.
They usually use 48 volts to supply 20mA of current in series with your phone. The phone is about 600 ohms and drops 12 volts at 20mA which leaves 36 volts that can be lost in the line. If you use 22 gauge copper wire, the resistance is about .016 ohms per foot, and 36 volts at 20mA is about 1800 ohms, so the maximum length would be 1800/.016 =
112500 feet or 21 miles. A larger gauge will increase the distance.-Bill
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