Telephone Circuitry

[7omos]

Dear Experts,

I have always been asked this question, why AC and DC currents are needed in a telephone Circuitry???

And to be honest with you i have been looking for a long time for the right answer but i couldnt find any website OR book to explain this to me.

So i would like to ask you people why? or if you have a handy website!

Thank you!

 

[Skogsgurra]

POTS (Plain Old Telephone System) used a battery to make things work. Often in the 24 - 60 V range. That is where the DC gets from. Not much AC available back in 18xx when telephone started.

The AC was introduced to make the bell ring. It was produced locally by hand-cranking. You don't see that any more. But AC is still used for ring signal. It is usually about 100 V and around 25 Hz.

The telephones of today use a mix of DC, tone signals and HF signals (the latter two are AC signals) as well as digital signals en masse.

You better google on. There must be lots of information out there.

Gunnar Englund

http://www.gke.org

 

[zeitghost]

Some chopped up some telephones for a tv programme some years ago, hoping to find carbon granule microphones.

Too late! Too late! Every one was electronic, with electret type microphones.

 

[OperaHouse]

I have both a HP 4943A and a HALCYON 701A that I use for non telcom purposes. If anyone is bored, can they tell me how they came up with the 1004Hz hold tone? There has to be a reason. A little history, the first generator frequency standard for Niagara Falls power generation was 166.667Hz.

Anyone have a manual for the HP 4943A? I bought it on an impulse and found the transmitter will only go up to 3,950Hz. It's got a lot of jumpers inside and wondering if I could change the upper range. My 701 will go up to 20K.

 

[fsmyth]

Without going into lots of detail, the 1000 Hz tones had to
be modified to eliminate data framing problems in high-speed
digital data transfer (SS-7). And as I understand it,
the 1004 Hz was relatively easy to implement, and within the
tolerance for the original 1000 Hz test tone, so test gear
did not require modification.

Check http:\\bama.sbc.edu for manuals.
<als>

 

[machmech]

Hello fsmyth

Thanks for that link, I could not use the original site everything could not be displayed for some reason. However I was able to use the mirror site, Here is the link for it.

Chuck

http://bama.edebris.com/manuals/