GB1521478A - Surface elastic wave delay line oscillators - Google Patents

Abstract

1521478 Surface wave devices; oscillators MARCONI CO Ltd 26 Aug 1975 [26 Aug 1974] 35152/75 Headings H3U and H3F An oscillator comprises an amplifier A having in its feedback loop a surface wave delay line including an interdigital transducer, the effective length of which may be varied by switching means connected to one or more sections of the transducer. The switching means is initially closed to provide a long transducer equal to the length of the delay line so that the oscillator operates with the desired mode. The switching means is then opened, either suddenly in the case of a mechanical switch or relatively slowly with an electronic switch, to provide a short transducer. When an externally introduced phase shift, e.g. from a frequency modulator, is changed linearly over a time equal to the delay time of the surface wave line, the short transducer enables a new oscillator frequency to be established immediately. The phase shift may be obtained by deriving a variable linear combination from the outputs of two spaced detecting transducers. The transducer of variable length may comprise a short section either between two switchable longer sections, Fig. 7, or at one end of a single longer section (Fig. 8, not shown). Alternatively a short and a long section may be provided one at each side of theother transducer (Fig. 10, not shown). In another modification, Fig. 9, the short and long sections are placed side-by-side opposite an extended transducer.