A double superheterodyne (or dual-conversion) radio is a high-performance receiver that converts the incoming radio frequency (RF) signal to an intermediate frequency (IF) in two stages, rather than one. By using two mixers and two local oscillators to produce two different IFs, these radios achieve superior selectivity, improved image frequency rejection, and high gain without instability. National RF-B20 Power Source: x3 AA size batteries, DC 4.5volts Frequency: FM 78-108MHz AM 530-1600KHz SW