The r.f. tuner selects the band, and amplifies the incoming signal to maintain a good signal to noise ratio. The gain is controlled by a.g.c. to suit the input signal strength. It converts the r.f. into i.f. by mixing it with the local oscillator to feed it into the first i.f. amplifier. It blocks the antenna pick-up signals in the i.f. range and prevents them from entering the receiver. It isolates the local oscillator signals from the antenna, due to the r.f. amplifier acting as a buffer, preventing radiation and interference to other receivers. It also rejects the image frequencies by means of r.f. selective circuits.