How to calculate the required ringing signal amplitude for my design?
Most modern telephone sets, modems and facsimile machines will recognize the Ringing Signal at amplitude of 35Vrms and above. A few facsimile models, and some older telephone sets will require minimum amplitude of 40Vrms or even 45Vrms to ring. When calculating the required output amplitude of a Ring Generator, the objective should be to deliver more than the minimum ringing amplitude to the loop’s end. The voltage drop on the loop can be calculated according to the typical line resistance, the loop length, connection resistance and the sum of the line’s serial protection resistors. Higher ring generator output amplitude can support longer loops. However, since ring generators are limited for specified output wattage and since telephone devices are current driven, lower output amplitude will allow for higher output current that translates to a higher REN.
