Transmission-Line Oscillators

The input impedance of a section of a lossless short-circuited transmission line less than one-fourth wavelength long is, theoretically, a value of pure inductive reactance (page 214). The condenser C of Fig. 38 is essentially a short circuit and is adjusted to a point such that the inductance offered by the line will be in parallel resonance with the capacitance between grid and plate. The inductors shown are radio-frequency chokes to reduce loss of high-frequency energy. Signal from the plate circuit is fed back into the grid-cathode circuit through the interelectrode capacitances; thus_; oscillations are sustained.

Figure 38. A simple oscillator using a resonant line to control the frequency. The radio-frequency "chokes" shown reduce high-frequency energy loss.