A VSWR meier is a sensitive high gain, high Q, low noise voltage amplifier tuned normally at a fixed frequency of 1 KHz at which the microwave signal is modulated. The input to the VSWR meter is the detected signal output of the microwave detector and the output of the amplifier is measured with a square- law-calibrated voltmeter which directly gives the VSWR reading Vmax/Vmin for an input of Vmin, after the meter is adjusted to unity VSWR for an input corre- sponding to VfaaOS shown in Figure. A gain control can be used to adjust the reading to the desired value. The over all gain is nearly 12S dB which can be altered in steps of 10 dB.
There are three scales on the VSWR meter. When the VSWR is between 1 and 4. reading can be taken from the top SWR NORMAL scale. For VSWR between 3.2 and 10, bottom of SWR NORMAL scale is used. When the VSWR is less than 1.3. a more accurate reading can be taken by selecting the EXPANDED scale, graduated from 1 to 1.3. The third scale at the bottom is graduated in dB.
Figure : VSWR METER