×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Telephone Circuitry

Telephone Circuitry

Telephone Circuitry

(OP)
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!

RE: Telephone Circuitry

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
www.gke.org

RE: Telephone Circuitry

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.

RE: Telephone Circuitry

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.

RE: Telephone Circuitry

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>

RE: Telephone Circuitry

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/

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources