A converter circuit (1) for RF signals for connection to the aerial input (3) of an RF superheterodyne receiver (2). In order to avoid a separate remote control of the converter circuit (1) use is made of the local oscillator radiation which is present at the aerial input of the connected RF-superheterodyne receiver (2) as an indication of the tuning frequency selected by the user with the tuning portion of the said RF superheterodyne receiver (2). The converter circuit (1) comprises a frequency search circuit (20) in which the frequency of the oscillator radiation is detected, an RF signal selector (11) which is controlled by the frequency search circuit (20) and by means of which the desired RF signal is selected from the RF signals applied to the converter circuit (1), furthermore comprising a modulator (18) which is also controlled by the frequency search circuit (20) and in which the selected RF signal is modulated on a carrier frequency which is determined by the tuning frequency and the intermediate frequency of the RF superheterodyne receiver (2).