This article was written to aid the new radio amateur in testing a homebrew balun.
Using a transceiver, SWR meter and 1:1 balun with resistor to test the balun:
You can test a balun by connecting a simulated antenna load on the output (antenna) side of the balun. Connect your transmitter ( with an SWR meter) on the input side. In the case of a 4:1 balun, use a 160 to 340 ohm resistor as your simulated antenna. (See Fig 1) If the balun is functioning properly, you should see a low SWR (less than 1.5:1) when you key your transmitter. This means that the 4:1 balun is matching the nominal 200 ohm load to 50 ohm (200/4 = 50). If you have a 1:1 balun, you can use the same test.
Simply substitute a 40 to 60 ohm resistor for the load. A 50 ohm dummy load
may substitute the resistor if available. The SWR should be 1:1 or very close to it. WARNING: The load resistors must be non-inductive and capable of dissipating the output power of your transmitter for a short period of time. If you turn your transmitter output down to 10 watts, you'll still need a heavy duty 10 watt resistor.
I have used this inexpensive old school method for many years but you could substitute your transmitter and SWR meter with a expensive antenna analyzer which will have the same end result.
Testing a 9:1 Balun with a Nano VNA:
Images: (Click on images for larger view.)
I decided to measure the "SWR and Impedance" of the 9:1 Balun with my NanoVNA. Although this is not the correct way to do it, it gives me some indication that the Balun is working. Let's call the measurement a fault finding mission. I used a 270 Ohm resistor across the connecting points and obtained the readings as depicted in the images.
Testing a 49:1 Balun with a Nano VNA:
Images: (Click on images for larger view.)
To test the balun before adding the wire and counter poise I used a 2K7 resistor on the ground of the coax connector and antenna connection. The attached NanoVNA image provide info on the results I obtained from the balun. I am sure the SWR readings will change once I add the antenna wire to the balun. The height and closeness of objects will also play a roll.
