what do u mean by it ? and how can i make it?However if it is not present, then you can obtain it by chopping a DC supply into pulses, and feed that to a voltage multiplier.
Or use a boost converter. Etc.
The phone line has -48 V on it when there is no activity. It could be as much as -60V amplitude (or greater).what do u mean by it ? and how can i make it?
the voltage from the phone line changes when it rings and when someone is talking..... isn't that right?