Controlled local oscillator with apparatus for extending its frequency range

In a tuner for tuning channels in a predetermined range of frequencies, apparatus comprising:

• channel selection apparatus for generating a tuning voltage having magnitudes corresponding to selected channels;
• a local oscillator for generating a local oscillator signal including a transistor having base, collector and emitter electrodes configured as a common base amplifier, said base electrode being connected to a reference potential point;
• a first varactor diode responsive to said tuning voltage and at least one inductor configuration connected in a parallel combination between said collector electrode and said reference potential point;
• and feedback means, including a capacitor connected between said collector and emitter electrodes, for conditioning said oscillator to oscillate at a frequency substantially determined by said tuned circuit in at least a portion of said predetermined range;
• RF means for receiving a plurality of RF signals and including filter means controlled in a tracking relationship with said tuned circuit means in response to said tuning voltage for selecting one of said RF signals in accordance with the magnitude of said tuning voltage;
• mixer means responsive to said local oscillator signal and to a selected one of said RF signals for generating an IF signal;
• and
• extension means, including a second varactor diode responsive to said tuning voltage connected between said emitter electrode and said reference potential point, said first and second varactor diodes being poled to exhibit capacitances which change in the same sense in accordance with the magnitude of said tuning voltage, for conditioning said oscillator to oscillate at a frequency substantially determined by said tuned circuit throughout another portion of said predetermined range in accordance with the magnitude of said tuning voltage.