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Phone Line Call Monitor

12/13/2009 12:37 AM

We use a regular land line to perform test-calls to test line clarity, line noise-levels, event timing, call-propagation, etc...

HELP: We use a PC-Based Telephony (PBT) system to dial out test-calls. We need a simple circuit so we can hook up a "second phone" to the same line via a simple line splitter. The "second Phone" will be used for monitoring the call being dialed out by the PBT, yet NOT interfere with the "Line Signaling", and not adding to the "Line Noise". We tried a speaker-phone-on-mute, but it drew too much from the line, and added noise.

ANY ideas are greatly appreciated.

Thanks!

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Leonardo Vezga
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#1

Re: Phone Line Call Monitor

12/13/2009 1:36 PM

How about an oscilloscope or spectrum analyser? Their high impedance inputs should prevent any loading of the telephone line (although these signal measuring tools may be overkill for your application).

Another (cheaper) option may be to add an amplifier to your test speaker phone (or stand-alone speaker so that it adds an additional signal buffer and doesn't draw as much from the telephone line under test.

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#2
In reply to #1

Re: Phone Line Call Monitor

12/13/2009 2:33 PM

The cheaper approach sounds more logical, however, would you be able to tell us how to create a "high impedance" at the component level? (resistor? capacitor? diod?) the ideal solution would be to use a "high impedance box with an integral amp-and-speaker? " ... or would could I adapt a powered PC speaker to do the job? ... Thanks!!!

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Leonardo Vezga
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#3
In reply to #2

Re: Phone Line Call Monitor

12/13/2009 7:10 PM

A standard amplifier has a high impedance input (the internal or integral op-amp provides the high impedance input).

http://en.wikipedia.org/wiki/Operational_amplifier

A powered PC speaker may do the job (possibly). The impedance may be too low, but it is a simple enough thing to connect up and try it to see if it works.

You need to be somewhat careful however as many countries have regulations which do not allow customers connecting unapproved electrical equipment to the phone lines.

There may be suitable commercial telephone test equipment available for sale or lease, but I don't know much about this area. You could try an internet search or perhaps call your phone company or telecommunications provider (they may know).

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