Lc-checker
The circuit is based on the grid-dip or absorption effect, which occurs when a parallel resonant circuit is coupled to an oscillator of the same frequency. Q1 operates in a conventional Colpitts oscillator circuit at a fixed frequency of approximately 4 MHz. A meter connected in series with the transistor's base-bias resistor serves as the dip or absorption indicator. The variable measuring circuit consists of C1, C2, and C3 and is connected to panel terminals as shown. C3 is loosely coupled to C2 in the oscillator circuit. This measuring circuit is tuned to the oscillator frequency with variable capacitor C2 set at full capacitance. When power is applied to the oscillator, the meter shows a dip caused by power absorption from the measuring circuit. Connecting an unknown capacitor across the test terminals lowers the resonant frequency of the measuring circuit. To restore resonance, tune capacitor C2 lower in capacitance. The meter will dip again when this point is reached. The capacitance across the test terminals can be determined by calibrating the dial settings of C2. Capacitor C4, a small variable trimmer in the oscillator circuit, compensates for drift or other variations and is normally set at half capacitance. This capacitor is a panel control, labeled zero, and it is used to set the oscillator exactly at the dip point when C2 is set at maximum capacitance. This corresponds to zero on the calibration scale.
The described circuit utilizes the grid-dip or absorption effect, which is a phenomenon observed in parallel resonant circuits when they are coupled to oscillators operating at identical frequencies. In this configuration, Q1 functions as part of a Colpitts oscillator, generating a stable output at approximately 4 MHz. The circuit includes a meter that is directly connected in series with the base-bias resistor of the transistor, which serves as an indicator for dip or absorption during operation.
The measuring circuit comprises capacitors C1, C2, and C3, which are strategically connected to panel terminals for user interaction. C3 is designed to be loosely coupled to C2 within the oscillator circuit, allowing for effective tuning and measurement. The primary tuning mechanism involves adjusting the variable capacitor C2, initially set to its maximum capacitance to align with the oscillator frequency.
Upon energizing the oscillator, the meter displays a dip, indicating the absorption of power by the measuring circuit. When an unknown capacitor is introduced across the test terminals, the resonant frequency of the measuring circuit decreases. To achieve resonance once more, the capacitance of C2 must be adjusted downward. When the correct capacitance is achieved, the meter will again indicate a dip, allowing for the measurement of the unknown capacitance. This process requires careful calibration of the dial settings of C2 to ensure accurate readings.
Additionally, the circuit incorporates capacitor C4, a small variable trimmer that serves to compensate for frequency drift and other variations that may occur during operation. This trimmer is typically set to half of its capacitance range. The panel control labeled "zero" is utilized to precisely calibrate the oscillator to the dip point when C2 is maximized, which corresponds to the zero mark on the calibration scale. This careful calibration ensures reliable measurements and consistent performance of the circuit.The circuit is based on the grid-dip or absorption effect, which occurs when a parallel resonant circuit is coupled to an oscillator of tbe same frequency. Ql operates in a conventional Colpitts oscillator circuit at a fixed frequency of approximately 4 MHz.
A meter connected in series with tbe transistor"s base-bias resistor serves as the dip or absorption indicator. The variable measuring circuit consists of Cl, C2, and 12 and is connected to panel terminals as shown.
12 is loosely coupled to 11 in the oscillator circuit. This measuring circuit is tuned to the oscillator frequency with variable capacitor C2 set at full capacitance. When power is applied to the oscillator, tbe meter shows a dip caused by power absorption from the measuring circuit.
Connecting an unknown capacitor across the test terminals lowers the resonant frequency of tbe measuring circuit. To restore resonance, tune capacitor C2 lower in capacitance. The meter will dip again when you reach this point. Determine tbe capacitance across tbe text terminals by calibrating tbe dial settings of C2. Capacitor C4, a small variable trirruner in tbe oscillator circuit, compensates for drift or other variations and is normally set at half capacitance.
The capacitor is a panel control, labeled zero, and it is used to set tbe oscillator exactly at tbe dip point when C2 is set at maximum capacitance. This corresponds to zero on the calibration scale.
The described circuit utilizes the grid-dip or absorption effect, which is a phenomenon observed in parallel resonant circuits when they are coupled to oscillators operating at identical frequencies. In this configuration, Q1 functions as part of a Colpitts oscillator, generating a stable output at approximately 4 MHz. The circuit includes a meter that is directly connected in series with the base-bias resistor of the transistor, which serves as an indicator for dip or absorption during operation.
The measuring circuit comprises capacitors C1, C2, and C3, which are strategically connected to panel terminals for user interaction. C3 is designed to be loosely coupled to C2 within the oscillator circuit, allowing for effective tuning and measurement. The primary tuning mechanism involves adjusting the variable capacitor C2, initially set to its maximum capacitance to align with the oscillator frequency.
Upon energizing the oscillator, the meter displays a dip, indicating the absorption of power by the measuring circuit. When an unknown capacitor is introduced across the test terminals, the resonant frequency of the measuring circuit decreases. To achieve resonance once more, the capacitance of C2 must be adjusted downward. When the correct capacitance is achieved, the meter will again indicate a dip, allowing for the measurement of the unknown capacitance. This process requires careful calibration of the dial settings of C2 to ensure accurate readings.
Additionally, the circuit incorporates capacitor C4, a small variable trimmer that serves to compensate for frequency drift and other variations that may occur during operation. This trimmer is typically set to half of its capacitance range. The panel control labeled "zero" is utilized to precisely calibrate the oscillator to the dip point when C2 is maximized, which corresponds to the zero mark on the calibration scale. This careful calibration ensures reliable measurements and consistent performance of the circuit.The circuit is based on the grid-dip or absorption effect, which occurs when a parallel resonant circuit is coupled to an oscillator of tbe same frequency. Ql operates in a conventional Colpitts oscillator circuit at a fixed frequency of approximately 4 MHz.
A meter connected in series with tbe transistor"s base-bias resistor serves as the dip or absorption indicator. The variable measuring circuit consists of Cl, C2, and 12 and is connected to panel terminals as shown.
12 is loosely coupled to 11 in the oscillator circuit. This measuring circuit is tuned to the oscillator frequency with variable capacitor C2 set at full capacitance. When power is applied to the oscillator, tbe meter shows a dip caused by power absorption from the measuring circuit.
Connecting an unknown capacitor across the test terminals lowers the resonant frequency of tbe measuring circuit. To restore resonance, tune capacitor C2 lower in capacitance. The meter will dip again when you reach this point. Determine tbe capacitance across tbe text terminals by calibrating tbe dial settings of C2. Capacitor C4, a small variable trirruner in tbe oscillator circuit, compensates for drift or other variations and is normally set at half capacitance.
The capacitor is a panel control, labeled zero, and it is used to set tbe oscillator exactly at tbe dip point when C2 is set at maximum capacitance. This corresponds to zero on the calibration scale.