Hi All,

I need to connect two ordinary phonelines for modem and voice transmission.
DC loop is held with a high impedance constant current sink.
Now I need some hints on AC coupling the two lines.

I have tried 2uF non polarized capacitors but they are large and expensive.
I have obtained some 600:600 telephone transformers but the Bourns
transformers had about 2dB insertion loss. I'm deliberate on putting the
right voltage level on each line so if I use a transformer I need
amplification.

Perhaps some of you could recall 2 wire repeaters from memory. These were
implemented using Negative Immittance Converters. Any schematics would be
appreciated.

The other way to implement it is using 2/4 and 4/2 wire converters (ie.
hybrids) and amplifying the 2 wire signals in each direction. Any schematics
doing 2/4 and 4/2 wire aplifying is appreciated.

Is there any special requirement if I want to use modem data transmission
over the connected lines?

I don't want to buy an expensive ready made 2/4 wire converter from Mitel so
unless you know a much cheaper one don't suggest me to buy one.

Looking forward to any ideas

Laszlo Cser
cserl@freemail.hu