UHF television tuner with electrical fine tuning

A UHF television tuning system operable in conjunction with a source of automatic frequency control signals comprising:

• a UHF television tuner having a continuously variable tuning shaft, rotation of which is effective to tune said tuner over the entire UHF television band;
• a channel selector shaft mechanically coupled to said tuning shaft;
• means for establishing a plurality of detent positions for said selector shaft corresponding to different ones of the UHF television channels;
• a voltage variable capacitor electrically coupled to said tuner, said voltage variable capacitor being operative to fine tune said tuner;
• a fine tuning potentiometer having first and second end terminals and a wiper terminal, said wiper terminal being direct current coupled to said voltage variable capacitor, one of said end terminals being direct current coupled to said source of automatic frequency control signals, said fine tuning potentiometer being operative to couple varying amounts of said automatic frequency control signal to said voltage variable capacitor to effect fine tuning to said tuner in response to an adjustment of said potentiometer;
• and
• means electrically coupled to at least one of said end terminals of said potentiometer for maintaining a substantially constant voltage between said end terminals over a predetermined range of values of the automatic frequency control signal, thereby causing changes in the value of the automatic frequency control signal applied to said one of said end terminals to be transferred to said wiper terminal substantially independently of the adjustment of said potentiometer.

A UHF television tuning system comprising:

• a UHF tuner having a housing, a continuously variable main tuning shaft rotation of which is effective to cause said tuner selectively to receive signals on all channels in the UHF television band, a channel selector shaft, means interconnecting said selector shaft and said main tuning shaft, detent means for said selector shaft for establishing a stop position of said main tuning shaft for each of the television channels in the UHF band, a mechanically variable capacitor mechanically coupled to said main tuning shaft, a variable frequency oscillator electrically coupled to said mechanically variable capacitor and having a frequency of oscillation that is adjustable upon rotation of said main tuning shaft over a range of frequencies corresponding to the entire UHF television band for determining the frequency of the signal received by the UHF tuner;
• a voltage variable capacitor electrically coupled to said oscillator for controlling the frequency of said oscillator and fine tuning said tuner independently of the operation of said main tuning shaft;
• a fine tuning potentiometer concentrically mounted over said selector shaft and electrically coupled to said voltage variable capacitor for effecting fine tuning of said tuner;
• a fine tuning shaft concentrically mounted about the outside of said selector shaft;
• and
• cooperating means including first and second opposed engaging members disposed concentrically about said selector shaft, said first engaging member being disposed on said fine tuning shaft and said second engaging member being disposed on said potentiometer for permitting direct engagement of said potentiometer by said fine tuning shaft, said fine tuning shaft being slidingly mounted on said selector shaft and axially movable to a first position in which said engaging members are engaged and solely effective to interconnect said fine tuning shaft and said potentiometer, and to a second position in which said engaging members are disengaged, thereby disengaging said fine tuning shaft from said potentiometer.