The centre frequency of the pre-selector is adjustable from the DIGI-SEL tuning knob on the front panel.Дouble conversion super-heterodyne system The pre-selector rejects unwanted out of band interference from multi-multi operation or strong broadcast stations, as your first line of defence against interfering signals. The pre-selector automatically tracks the intended signal, keeping the pre-selector's bandwidth centred on the operating frequency at several kHz steps (minimum). The pre-selector works from 1.5MHz to 30MHz. The two roofing filters dramatically improve the blocking characteristics from strong adjacent signals. This is not an optimal design for SSB, CW, or AM modes.

Typically, transceivers use only one broad 15 kHz roofing filter for all modes. The IC-7800 switches between these two roofing filters depending on operating mode. One is 15 kHz filter for FM mode and the other is 6kHz filter for SSB, CW, AM and data modes. The IC-7800 has two roofing filters before the 1st IF amplifier stage. The mechanical relay prevents 2nd order distortion at the primary stage of signal processing. The IC-7800 uses highly reliable and durable mechanical relays for BPF switching instead of non-linear semi-conductors which cause distortion. Mechanical relay BPF (Band Pass filter) switching and two roofing filters

This allowed us to explore new technical dimensions such as a double conversion super-heterodyne system, mechanical relay BPF switching and two roofing filters. To achieve this superior receiver performance, Icom's engineering team completely reviewed the whole analogue circuit and matched it to the DSP units. Icom's 40 years of analogue RF circuit experience combined with cutting edge digital technology results in an astonishing 110dB receiver dynamic range and a +40dBm IP3 in the HF bands. Further details of Icom IC-7800 Base Station Amateur Radio

Ic-7800 dual channel version