A straightforward way to test a 4:1 balun is as follows:
- Disconnect the output side of the balun from your antenna or ladder line.
- Locate a NON INDUCTIVE (Carbon composition, for example) 200 ohm resistor and connect it directly across the output terminals of the balun.
- Using an antenna analyzer, you should find low SWR (1.2:1 or below) across the entire operating range (1.8 to 30 MHz) of the balun.
If the SWR does not read low across the entire operating range, there is a problem with the balun.
Note
If you're testing a 1:1 balun, connect a non-inductive, 50 ohm load across the output terminals of the balun for the test.