Radio antenna tuning circuit
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United States of America Patent
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Nov 16, 1993
Grant Date -
N/A
app pub date -
Apr 30, 1991
filing date -
Apr 30, 1991
priority date (Note) -
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Abstract
The present invention provides an antenna or preselector tuning method and circuit that tunes an antenna or preselector in a very short period of time. The circuit of the present invention does not rely on measuring the magnitude of the signal strength at the output of the receiver as do many prior art antenna tuning techniques. With the present invention a radio frequency (RF) oscillator set to the desired receiver frequency generates an excitation signal which is lightly coupled to the antenna tuned circuit through a network. A phase detector then compares the phase of signal established in the antenna tuned circuit with the phase of the excitation signal to produce an 'error' signal indicative of the phase shift of the excitation signal as it passes through the network. Using this 'error' signal and locked loop (PLL) techniques, an antenna tuning voltage is created that results in a zero phase shift through the network.
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