crystal controlled sinewave generator

between the oscillator and the aerial above the audible threshold (between The applications of simple designs are not always restricted to those of a single circuit. A combination of two (or more) circuits can offer new perspectives. For instance, combining a crystal controlled frequency synthesiser and a digital spot sinewave generator produces a very stable sinewave generator. This "hybrid" uses switches to select the output frequency in 1 Hz steps. Figure 1 shows the crystal controlled frequency synthesiser section. It is a slightly modified version of the circuit published in the Summer Circuits 1979 issue of Elektor. The heart of the circuit is formed by a phase locked loop (PLL). A very stable frequency is fed to one input of the PLL (IC7) and its output is passed through a variable divider chain before being fed to the other PLL input. The PLL will try to equalise both input frequencies and adjust its output frequency accord- ingly. Therefore, when the division ratio is se...