From: "Mortel" <[NOSPAM]firstname.lastname@example.org>
Subject: Re: Telephone Hybrid circuit schematic
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Date: Sat, 18 Jan 2003 08:37:22 -0500
NNTP-Posting-Date: Sat, 18 Jan 2003 08:37:14 EST
Organization: Bell Sympatico
"Terry King" wrote in message
> > Jean-François,
> There are a few other possibilities. Typically an
> opamp or two is used in a circuit which cancels
> out the signal being sent out from the signal being
> received. This has to happen at "some" impedance,
> and a problem is that the telephone line impedance varies
> and affects the isolation. You can build a circuit
> with a 'null' pot to adjust this. With this, you
> only need a single isolation transformer (typically
> 600/600 ohms or 600/900 ohms) to the phone line.
> You have the correct terminology: "Telephone Hybrid".
> Do more of a search on that.
> I can probably find my schematics somewhere... I once
> built some of the first radio station "Telephone Talk
> Program" systems, back about 1968 or so. I actually
> built my own opamps to build the hybrids. Seems
> ridiculous now, with opamps 4 for 25 cents US.
> If you can find an actual modem schematic, the DAA
> "Data Access Arrangement" section will contain the
> hybrid circuitry.
> Let us know if you find what you need...
> Geez.. I just looked back, and realized I
> "Answered The Geek Call"!! Oh, well. Guilty...
> Regards, Terry King ...In The Woods In Vermont
Thanks a lot Mr. King for the information,
I'll continue my research in this path and Mr. Leduc gave me a good appnote
about DAA circuitry, thanks to him !
Oh and sorry for the geek thing, if I knew you built your own opamp in 1968
I would probably have called you master :o)
Thanks to all who helped me ! Electrical engineering diplomas don't grow on
Have a nice day !