Part 8 - Design, Calibration & Performance of Standing-Wave-Ratio Meters - Location of Current Transformer, Operating Reminders, and Software

Program Notes (Continued)

Location of Current Transformer
The circuit diagram shows the current transformer in series with the source. To make internal source resistance exactly equal to Zo, deduct the transformer's input ohms from Zo before entering source resistance into the program. Insofar as the source is concerned the voltage divider impedance is in shunt with the load.

The program assumes RF power dissipated in the divider chain is negligible.

Operating Reminders

• After calibration the meter will accurately indicate all parameters only when the source (transmitter) internal resistance is equal to Zo. This condition is checked by varying the load and looking for constant forward power indication.
• When the source resistance is not equal to Zo only forward and reflected power will be accurately indicated. Reflection coefficient and SWR will be indicated accurately only when RC = 0 and SWR = 1. (The primary purpose of the meter).
• Other values of RC and SWR can always be calculated from power readings.
• The meter can be made to indicate RC and SWR directly by adjusting sensitivity on every occasion a reading is required. But this necessitates re-calibration of the wattmeter scales.
• It is possible to prevent this adverse interaction between meter functions by selecting from the front panel a different sensitivity control for each of the meter scales. The program leaves the experimenter to design the circuitry.
• The data screen displays both indicated and true values for comparison.

Run this Program from the Web or Download and Run it from Your Computer
This program is self-contained and ready to use. It does not require installation. Click this link SWRMeter then click Open to run from the web or Save to save the program to your hard drive. If you save it to your hard drive, double-click the file name from Windows Explorer (Right-click Start then left-click Explore to start Windows Explorer) and it will run.

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