Temperature responsive transmitter

A temperature responsive transmitter in which frequency varies linearly with temperature includes two identically biased transistors, Ti, T2 connected in parallel. A capacitor Cl, which reflects into the common bases to generate negative resistance in parallel with the capacitor, is connected to the common emitters. A crystal 30 is in parallel with the capacitor and the negative resistance. Oscillations occur if the magnitude of the absolute value of the negative resistance is less than the positive resistive impedance of the capacitor and the inductance of the crystal. The crystal has a large linear temperature coefficient and a resonant frequency which is substantially less than the gain-bandwidth product of the transistors to ensure that the crystal primarily determines the frequency of oscillation. A high-Q tank circuit having an inductor, L, and a capacitor C2 is connected to the common collectors to increase the collector current flow, which in turn enhances the radiation of the oscillator frequency by the inductor.