Viking RG-4 Ringing Power Boost

Power Boost Features: Duplicates incoming ring cadence, allowing it to be compatible with custom ringing features Capable of ringing four 1 REN or eight 0.5 REN telephones True Sine wave ring signal output Boosts ring to 4 REN Caller ID compatible Easy installation Compatible with distinctive ringing services Will not affect normal line operation Reshapes troublesome square wave ringing Fax and modem compatible Not compatible with pulse dialing Ring Generator (Model #: RG-10A) may be used for single line higher drive output applications up to 12 REN 2 Year Limited Warranty $87.85

source https://www.vikingtelecomsolutions.com/viking-rg-4-ringing-power-boost.html