19-05-2012, 04:52 PM
Measurement of unknown impedance
9 Impedance measurement.doc (Size: 88 KB / Downloads: 27)
THEORY: -
The complex impedance ZL of a load can be measured (Eqn. 1) by measuring the reflection coefficient. The phase angle ΦL of the complex reflection coefficient ΓL is determined by measuring the distance of the first voltage standing wave minimum from the reference point and the magnitude of the same from VSWR value S.
PROCEDURE: -
1) Keep the control knobs of Gunn Power Supply as below -
2) Keep the cavity meter completely detuned, and the attenuator at the top most
position (to get un-attenuated signal).
2) Switch ON the Gunn Power Supply.
3) Bias the Gunn diode at proper voltage (say 8v). Do not exceed the bias voltage
above 10 volt.
4) Set the micrometer of Gunn Oscillator, Mod. Freq. knob, pin bias knob and the
tunable probe to get maximum reading on the VSWR meter.
5) Now gradually reduce the cavity resonance frequency to get a dip on the VSWR
meter scale. Measure the frequency from the dial of the of frequency meter.
7) Connect the unknown load at the output of the slotted section. Move the probe along the slotted line to get maximum deflection.
8) Adjust VSWR meter gain control knob and variable attenuator until the meter
indicates 1 on the normal dB SWR scale.