Double super heterodyne receiving method and its reception circuit

摘要

PROBLEM TO BE SOLVED: To obtain a receiver with a simple structure without being limited by electromagnetic wave environment by making two local oscillation frequencies have a correlation, simultaneously varying them and arbitrary varying the 1st IF frequency while keeping each of the frequencies of reception, the 2nd IF and reference fixed. SOLUTION: The receiving RF signal is fixed with a signal f1LO from the VCO 16 of a 1st local resonance LO in a mixer 12 and is to be converted into a 1st IF f1IF, and then f2LO that the f1LO is A-divided by a variable divider 17 by the control of a variable dividing control circuit 23 is inputted to a mixer 14 and outputting to a demodulator as a 2nd IF f2IF, and at the same time, it is B-divided by a variable divider 18 and then it is C-divided. The frequency fREF of a reference oscillator 20 is D-divided by a divider 21, and the VCO 16 is controlled based on the result of comparison with the C-divided frequency. Thus, the frequencies of the 1st and the 2nd LO are varied simultaneously and having a necessary relation by controlling the dividing values of the variable dividers 17 and 18, so that the prescribed 2nd IF signal is outputted while keeping the reference oscillation frequency constant.