I’m assuming a landline phone needs some source of power to amplify and convert signals. Is there a power cord embedded in the phone jack?
Also on the topic on phones, I remember in Primer how two characters were arguing over whether a duplicated cell phone would both pick up the same call, or whether the network would search until it found an instance of the receiving phone, then stop looking. The debate was not resolved in movie - does anyone know what the answer is?
Phone company has their system on generators so the system can run without regular power. But if trees fall on a phone line it won’t work. We got hit by a hurricane and my parents got their power back before their phone worked.
Yes, the phone line carries its own power. True for conventional landline phones, not for cable/FiOS phones.
Your landline telephone draws it’s DC 70v power from the telephone lines. Essentially, using the phone completes a circuit. The source of the power is, IIRC, specifically not a part of the same sub-station that powers an area, so that emergency services have a greater chance of still being in place during power outages and events which can precipitate them.
No, the power required comes down the same wire the signal does, in fact the signal provides the power.
if the blackout took out the exchange the phone would stop working, and if it’s a powered phone (such as a cordless) it will stop working too.
Landline phones receive their power from the telephone company’s Central Office. It is generally a large building with no windows anywhere from next door to a few miles away. Your landline phone does not require any power from your household.
The Central Office does use commercial power, but also has battery backups and generators. They also have contracts for fuel delivery in the event that the power outage is extended.
I’m less clear about the answer to your last question. Assuming each of the “duplicate” phones are in separate cells, I’m quite confident only one would connect, though perhaps both would ring. I also suspect that the wireless companies would detect duplicate SIMs and disable both, as it would be a sure sign of fraudulent activity. In that case, neither would ring, and neither would connect.
I remember asking my wife this very question after seeing Primer: she is an engineer for one of the big cellular companies. I may be misremembering, but she thought that both would ring, assuming they were in the same area. There would be a “you have a call” signal sent out from a regional group of cell towers based on where your phone had last registered itself - if both phones got that signal both phones would ring. I’m guessing that things will go haywire pretty quickly once someone tries to answer …
The standard old fashioned telephone is a piece of sheer genius that everyone takes for granted (and many now consider obsolete). They were able to get a ring signal, an off the hook detection signal, and voice signals in both directions all onto only two wires, using little more than complicated little coils of wire to make it all work.
The two wires have 48 volts DC across them, fed through relay coils which have enough impedance in them to limit the current. They superimpose a ring signal of 90 volts at 20 Hz on top of this to make the phone ring. When you answer the phone, the switch closes the connection, causing current to flow. This the current is fed through relay coils, this causes the relay to switch on and the phone system knows you’ve picked up the phone. The earpiece and voice coil are both in series and have the current from the switch flowing through them. Any change in current will cause the earpiece to move back and forth, creating sound. Likewise, any sound will cause the mouthpiece to vibrate, and modulate the current. Normally, this would cause your own voice to be REALLY LOUD in the earpiece, but they use a very creative coil to make it so that your own voice is much quieter in the earpiece than the voice from the other end.
All that on freaking two wires, using nothing more than magnets and coils of wire.
The phone company’s switching station has big 48 volt batteries. If the power goes out, they can run on batteries for some time. If the power goes out for too long, they can switch on electric generators to recharge the batteries and keep things going. They can run for quite a while without power from the power company.
Here’s a picture of the batteries at a phone office. They are around 2 volts each and connected in strings of 24 to get up to -48v (positive ground). They are connected to the rectifiers with 750 mcm copper cable which about 3 pounds a foot and maybe an inch and a half to two inches across. Stuff is a bear to pull and dress into place. I once saw a wrench completely evaporate when it was dropped across the buss bars above one of these strings. I can’t remember what the amperage was on these since I haven’t worked with them for 15 years or so (I went from central office to working cellular systems).
Cable companies will typically install a battery backup at the user’s home. It just won’t last indefinitely.
The battery on my cable phone will supposedly allow 8 hours of conversation. But it does illustrate why you should have at least one non-cordless phone on your line.
Also a good idea to have at least one phone in your home still be of the corded variety so you can use it during blackouts. I know people who have switched all their home phones to the cordless type which become useless when the power is out.
Actually, we started with one wire to the house, and used the ground for the return path. In the earliest days, this was strung on fenceposts - and sometimes, they used the existing fence wire. My grandfather used to tell me stories about working on this type of plant. He claimed the most common cause of noise on the line was a poor ground connection, particularly in drought years. Before they sent someone out, they’d ask the customer to go pour a bucket of water on the ground rod, which would usually clear the problem up.
As metioned upthread, the ILECs[sup]1[/sup], CLECs[sup]2[/sup], and RBOCs[sup]3[/sup] all have battery back-ups and diesel generators for recharging the batteries located at their Central Offices. In addition, if you are in an area served by fiber optics, the converter from fiber to copper will also have a diesel back-up generator. You can sometimes see these by the side of the road. They sometimes look like a big, orange box - about the size of a Cooper Mini.
There are all these backups because the FCC requires these telephone companies to provide reliable service 99.999% of the time. It’s called the rule of five nines. It’s also why I will not ever go to Cell-phone only or to a VOIP service like Vontage. If I pick up the phone in an emergancy, I want to make damned sure there is a dial tone.
1 - Independent Local Exchange Carriers. Windstream, Embarq, and the like.
2 - Competitive Local Exchange Carriess. Deltacom, Paetec, IXC, and the like.
3 - Regional Bell Operating Companies. The Baby Bells born from AT&T’s break-up.
I’ve heard that phone companies are required to provide emergency access even if there’s no phone plan setup. Is that true? I believe it’s true for payphones but what for just random phone jacks in your house?
It is true. Even if you are not paying for service, you can still dial 911 from jack that is connected.
But there are more services than 911 you may need in an emergency.
When I worked for the Bell System on switches, I believe that they actually ran on batteries, which were continually being recharged in normal operation - so no switchover is necessary. In the good old days there were special Bell System batteries - a chemist friend of mine swore by them for some of his independent work for DuPont. And of course central offices had generators.
An awful lot of design went in to ensure reliability in all sorts of circumstances. For instance, the ICs used for transmission equipment had to survive and work for I think 15 minutes even if the fan in the card cage went out.
Though those usually have a battery backup (we’ve got FIOS and part of the install was having that installed near where the cable comes into the house).
Mrs. FtG is keen on replacing the land line with an Internet phone. The problem as I see it is that the cable Internet goes out completely every time there is a power glitch. Sometimes not coming back up for hours. So for me, it wouldn’t matter if my end had power (or that there was power all down the line) if the cable company has to reset it’s hardware.
Is this not a problem with other people or do I just have lousy service?
