i want to amplify my telephone


2002-01-07 6:02 pm
AudioFreak is correct, that attaching a non-approved device to the phone line is illegal. IIRC in the US it contravenes FCC regulations (Federal Law). You're also likely to damage the exchange electronics for your line.

The only way to connect non-certified electronics to a phone line is via a line isolation unit (LIU), which itself must be certified. The LIU usually consists of a small isolating 1:1 transformer and sometimes a zener, so if you pump too much level through it it'll saturate the core or be clipped by the zener. The LUI is designed so that it will protect the network under fault conditions.

If you connected an amp illegally and drove excess level down the line, that level would not make it to the receivers end. When the signal gets to the exchange it is either digitised, or modulated onto a carrier for transmission through the network. Either way the level will be controlled by an AGC amp before either of these, and the level clipped if neccessary to ensure the network cannot be overdriven. Modern exchange equiptment would protectively shut down in the face of such high levels, and log a fault. Depending on how the exchange is configured, it may reset automatically, or stay off until a maintenance technician looks at it and resets it manually. Whilst it's in a protective/fault mode, you have no functioning phone line. You are likely to be billed for a service call, and if the carrier thinks you have done deliberate damage, can make your life difficult, even without civil or criminal proceedings being involved.

In a nutshell, it won't work, so don't do it. Be nice to your Gran, and give her some respect by just speaking up so she can hear you clearly. It'll also take a lot more effort futzing around with gear to make it work right, than it would to just speak up.
Remember, you'll be old one day too. (aaaaargh! I sound like my mother)