SYNTHESIZER RECEIVER

PURPOSE:To automatically switch the selectivity characteristics, by easily detecting the presence/absence of an interference signal, through a DC component detection of a frequency detecting signal at a frequency near a desired signal frequency. CONSTITUTION:Taking a frequency of a desired reception signal as f0, the reception frequency of a receiver is set to f0tDELTAf ahead the start of reception. When no interference signal exists or there is an interference signal negligibly small, a detected DC component is V2 apart from V0. If an interference signal not negligible exisis in a frequency f', the detected DC component moves to V3. Depending whether or not this detected DC component exceeds a threshold value Vt1, the pass band width of the receiver is automatically selected, allowing to obtain the receiver convenient in use. The receiver like this can easily be constituted by using a microprocessor and a voltage comparator. In case of a normal FM reception, it is suitable to select DELTAf=+ or -100kHz.