Voltage controlled UHF transistor oscillator - has octave range output using varicap diode and resonant line in base circuit with impedance shunt across diode removing parasitic resonance

摘要

The oscillator consists of a transistor (2) whose transition frequency is greater than twice the maximum oscillator frequency. The transistor is connected in common collector mode with a resonant circuit coupled to its base by a capacitor (19). The resonant circuit is a section of line (1) of predetermined characteristic impedance connected at one end to the transistor and at the other to a variable reactance formed by one or more varicap diode which is connected at its other end to ground. The diode is shunted by a second section of line (24) of significantly higher impedance whose length is chosen inversely with the maximum operating frequency. The diode serves to shift the effect of the parasitic inductance of the diode out of the operation band. The varicap diode may be two diodes connected back to back so that they can be reverse biased despite the shunt. The resonant lines and chokes of the circuit may be striplines formed by printed circuit techniques on a dielectric base, the other components being soldered in place. The circuit uses low cost commercial components, and may be controlled to oscillate over the range 1.2 GHz to 2.3 GHz and may be used for down conversion of satellite broadcast TV without switched reactances.