Ah finally a topic for me,
This is not as easy as it sounds the AC impedance can vary depending on lots
of things these days.
You may find that the PABX comes complete with adaptive ballance, so the
length of the line is not important. I fear that your case is more complex
due to you working on the 2 wire side. In this case you have to have a
terminal ballance return loss of better than 30dB. As for send and receive
stuff it is quite simple, I have posted this information many times before.
The impedance that you are looking into may be complex (Will for new PABX,
not for old) but a nominal TN6 (600R) will do this. But then I am getting
off track here. It would seem that your are attempting to go into the 2 wire
side? I suspect that this is a Ring out Loop in line ie provides battery and
ring and detects off hook etc. If this is the case, you have done all the
hard work and the impedance should be a walk in the park. Ok so here is the
deal:-

        PABX sends to customer -6dBr
        PABX  receives from customer 0dBr

 Where 0dBr is the reference point in the MDF and is a nominal voice power
of -15dBmO (600ohms)

In the above it is assumed that the line will have a loss of 3dB, in any
case the PABX like any nominal (Note that as all are not the same) will have
a switching loss of 6dBr from the receive to the send, and that is all that
you need.
Oh yes overhead response, your circuit must operate up to 3.14dB above the
nominal maximum levelm thus at 600ohms you need to be able to receive
+3.14dBm


Dennis





> -----Original Message-----
> From: Jane Ifurung [SMTP:jane_ifurung@YAHOO.COM]
> Sent: Sunday, 26 March 2000 0:50
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      (ot) measuring phone
>
> Does anyone of you knows how to measure the phone line
> impedance?
>
> I have a voice multiplexer project and I interface to
> Private Automatic Branch Exchange. I can't balance the
> transmit and receive gain of my system. I suspect it
> depends on the phone line length and impedance.
>
> I'm hoping for your answers.
>
> =====
> *~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~
> Jane Ifurung
> UP Diliman, Quezon City
> 920-5301 loc 5854
> (632)731-3545
> jifurung@eee.upd.edu.ph
> *~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~
>
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