Telephone cable voltage

telephone cable voltage

Hello all,

How about the telephone cable voltage?

Regards,

Davy Zhu

use telephone cable voltage uk

What about it?

what voltage should be at a telephone cable

Hi davyzhu,

Check this post :

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Look at TBR21. It give all phone line parameters for Europe.

Replace * by t

Regards

davyzhu said:

Hello all,

How about the telephone cable voltage?

Regards,

Davy Zhu

Click to expand...

Ok remember telephone is no more than 64kbps as it operates. This is usually. In USA it is 64kbps that I know.

Practically the operating voltages of telephone systems can vary from 24V to 60V depending on the application, although 48V nominal voltage is the most commonly used. When telephone is on-hook down the line voltage is usually 1-3 volts. It is 8-10 volts when off-the-hook.

Remember are several systems of telephony in the world.
Now in the line voltage theoretically should be the same for each state separately for a matching load.

European country main telephony standard use E1 signal, which run at 2.048Mbps, and contain 32 channels of 64Kbps. One phone line is routed to one channel.

In North America, the standard is T1, which is 1.544Mbps, with 24 channels of 64Kbps. One phone line is routed to one channel.

However, there is a catch. Those 2 standards come in different 'flavors'. For example, for T1, you can have what's called 'unframed', 'super-frame' and 'extended super-frame' (the most populars). the unframed T1 signal give 64Kbps, however, other signals give only 56Kbps of payload. The framed signals use some of the bits of the T1 payload as extra framing signals (to pass along extra infos).

This is why the modems standards can only go up to 56Kbps (which are by the way a pretty remarkable piece of technology, to be able to encode analog signals so that they get transformed to digital signals in the CO with using all of the avail bits).

The twisted pair cable that comes to your home in form of Tip and Ring in the RJ-11 connector is normally at -48V. You measure it sometime with a DMM. The battery voltage is the central office is specified nomially at -48V, hence the loop voltage is rated -46V to -55V. This is just the DC voltage for detecting the loop current. Of course when a phone call is considered, a ringing cadence AC signal around 20Hz is superimposed to this DC level (-48V) to bring it up to 90 to 110 Vrms.