Crystal-controlled radio frequency generators

1,144,459. Transistor oscillator circuits. STANDARD TELEPHONES & CABLES Ltd. 9 Aug., 1966, No. 35522/66. Heading H3T. A crystal controlled oscillator operable at a first frequency using a fundamental mode of oscillation, and at a second frequency using an overtone of oscillation is provided with a high pass filter 25 which may be included in the oscillatory loop, when operating on an overtone, to prevent operation at frequencies below the required overtone. As described ganged switches 18, 19, 39, 40 may connect to an amplifier 16, 44 either crystal 30, operating in its fundamental mode, and a capacitive coupling 20, or alternatively crystal 32, operating at an overtone, and the high pass filter 25. Further crystals may be included for selecting other frequencies. In an alternative arrangement, Fig. 3 (not shown), separate amplifiers are used for each crystal.