| 摘要 |
<p>A television tuning system employing a varactor tuner in which the local oscillator frequency is time sampled by an asynchronously gated counting system to provide tuning information for a channel number computer. The computer has a presettable modular scaler and presettable units and tens counters to derive the corresponding channel number and a fractional portion of the intrachannel spacing. A comparator is coupled to the channel number computer for comparing the derived channel number information with the desired or input channel number information. A keyboard-selected channel number is encoded and stored in a memory which supplies the information to the comparator and to a decoder display unit for visually displaying the selected channel number. The memory also supplies information to a band decoder which provides band preset information to the channel computer and selectively activates the VHF and UHF tuners. The comparator controls a ramp voltage source for adjusting the tuning status of the tuner until: 1) equality exists between the derived and desired channel numbers and 2) the modular residue representation of intrachannel spacing is within a predetermined range.</p> |
