Investigation of Tunnel-Diode Oscillators Activated on the Internal Capacitance of Their Coils

Comparison of two tunnel-diode oscillators is performed, one of them having a solenoid pick-up coil, while another one has a single-layer flat-geometry coil. Oscillators operate in the frequency ranges, respectively, 6-25 MHz and 8-24 MHz and the coils had approximately equal inductances. These oscillators have been activated both without and with an external capacitance C(0) in their resonant circuit, i.e., the studied oscillators could be activated also with their internal (own) capacitances C(c). It was succeeded to obtain more stable oscillations in case of flat coils. The analysis of data indicates that this fact is a consequence of a relatively high value of the own capacitance C(c) of the flat coils as compared to their parasitic capacitance C(par) with respect to the environment. This causes the advantages of flat-coil based oscillators. Also the inductance and the quantity C(c) + C(par) have been determined for both coils from the data of measurements.