Rolls MO2020SE Testoscillator Sine/Square Wave GeneratorTechnicians and electronic hobbyists in need of a portable signal generator for electronic testing of audio frequencies will rejoice with the Rolls MO2020se Testoscillator, which generates both sine and square waves and features independent level controls. The unit's frequency range is from 20 Hz to 24 kHz and includes a variable control knob. The frequency can also accept a 1. 2 to 5 VDC VCO input on a 1 4" input jack for external frequency control.