Q Meter Study

Bootstrap RF Voltmeter LF Ferrite Q Study T68-2 30T #22 Q Measurement T80-2 36T #20 Q Measurement T80-2 80T #26 Q Measurement

T50-2 36T #24 Q-Curve Measurement

Using Q-Capacitor and fixture below Add 330pF C0G at 3 and 2.2 MHz Micrometals Reference, Page 15

Q-Capacitor Prototype

400pF Variable Capacitor. Shaft ground wire required

Q-Meter Prototype

DG1032 AWG Settings

Q Meter Measurement

250 Full Scale Q Vin = (50 / 250) * 6.9 = 1.38Vrms Injection Transformer = FT50-43 50:1 Turns (Fair-Rite 5943000321) 1dB BW = 7kHz to 14MHz DUT = T50-2 36T #24 and 330pF C0G Micrometals Q Curve Page 15 Measured Q = 205 V-Meter 3dB BW Q = 207

SimSmith Model with DUT Q=207

Injection Transformer Fixture Schematic

RF Voltmeter Prototype

Schematic

R1 : Added for 50Ω Input Impedance R2 : Set AD8055 bias to 5V minimum R3 : Detector linearity adjustment "1N5711 Response with 10 kΩ Load with and without Compensation Amplifier" BF256B and 2N2907 1dB BW limit = 10 MHz Maximum RFin = 1.5 Vrms RFin = 17.25 / DCout (2.5Vdc scale = 6.9Vrms scale)

Injection Transformer, With Capacitive Divider, Fixture

Oscilloscope Example

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Previous Lab Notes

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Injection Transformer = FT50-43 50:1 Turn DUT = T50-2 37T #24 with 330pF C0G DG1032 AWG = 100 mVrms at 3.2978 MHz VOM set to 2.5V DC, Full scale = 1V RFin Full scale Q = 500 DUT Q = 300

VNWA S21 Q Measurement

Injection Transformer = FT50-43 50:1 Turn DUT = R40C1 36T 330/46 with 330pF C0G DG1032 AWG = 36.3 mVrms at 917.576 kHz VOM set to 2.5V DC, Full scale = 1V RFin DUT Q = 1 / (.0363 / 50) = 1377 DUT VNWA BW measured Q = 1150 (same capacitor)

Injection Transformer Board

FT50-43 50:1 Turns

HP-400E Measurement Example
DUT = T50-2 37T #24 with 330pF C0G

Photos by Everett Sharp, N4CY

AWG set to 200mVrms at resonant frequency

Q = 250 * 0.83 = 208
VNWA Measured Q = 229

SimSmith Example

RF Voltmeter Prototype

Schematic

R1 : Added for 50Ω Input Impedance R2 : Set AD8055 bias to 5V minimum R3 : Detector linearity adjustment "1N5711 Response with 10 kΩ Load with and without Compensation Amplifier" BF256B and 2N2907 1dB BW limit = 10 MHz Maximum RFin = 1.5 Vrms Total gain = 0.888 * 2 * 1.414 = 2.51 DCout = RFin * 2.51

Prototype Breadboard

Q-Meter Prototype Schematic