Newsgroups: sci.electronics.design,sci.electronics.misc
Subject: Re: Need tap into Telco line.
References: <[email protected]>
[email protected] writes:

> Here in rapidly degenerating S.Africa where the judicial system has
> become non functional, and majority controlling shareholders are 
> looting my inheritance by extracting all value for themselves by
> way of [self appointed - legally] director's fees, I need some technology
> leaverage.     Obviously in a non-functioning society, you must DIY.
> 
> The looter's actions indicate that they are tapping into my phone line 
> which goes through their PABX.
> 
> In the telco-room I've located my pair and their pair on the 
> tag-blocks.
> 
> How would I best hear their speech ?

Read those documents:
http://www.epanorama.net/documents/telecom/telerecord.html
http://www.epanorama.net/documents/telecom/teleinterface.html

Connect the output of the circuit to suitable listening amplifier 
that can send the amplified sound to headphones or some other 
telephone line. 

> Since I've got easy regular access to the tag-blocks, and I seldom
> receive calls, I could set-up occasionally for a few hours at a time.
> Ie. not use a long-term set-up.
> 
> My first thought is to just temporarily connect my pair to theirs,
> observing the polarity, and while leaving mine on-hook, just
> tap-off my line into an amplifier, which I can hear while
> I'm working.
> 
>  A second refinement, would be to use capacitive coupling
> to their pair.

Cpacitive coupling to the pair and amplification near 
the coupler is a working approach to listen to signal 
on telephone line. 
 
> I need to terminate my side with a high impedance, so that
> the capacitive coupling can also have a high impedance.
> So that it becomes insignificant when I receive or make a call.
> 
> If I remove my handset, so that only the audio amplifier 
> terminates my line, during 'listening in', would it work ?
>  
> And then by just connecting my handset and/or modem
> could I expect to operate without significant cross-talk to
> the looters line ?

Propably not.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/