| 摘要 |
PURPOSE:To give the continuous switching to both the higher- and lower-rank local oscillation frequencies for the radio receiver or the reception frequency selecting device of the spectrum analyzer. CONSTITUTION:The input signal of terminal T plus the output of local oscillator L1 are applied to mixer M1, and the output of M1 and the output of local oscillator L2 are applied to mixer M2. Thus the fixed intermediate frequency output is obtained. The frequency of L2 varies continuously according to the revolution of knob C2 of fine adjuster F, and this variation range is equivalent to the frequency change of the 1st stage of L1. And the addition and subtraction pulses are generated by pulse generator P by setting knob C2 at the maximum and minimum positions each, and at the same time C2 has a continuous turning. When rough adjuster C1 is set to a proper switching position, the corresponding voltage is obtained through adder S to decide the frequency stages of L1. The value of counter N varies according to the maximum and minimum setting of C2 and then applied to adder S after the D/A conversion to increase and decrease the stage position for the frequency of L1. |
