Antenna Tuning with a NanoVNA

The NanoVNA is a $50 vector network analyzer that has no business existing at that price point, and yet here it is. Here's how I used it to tune a quarter-wave antenna for 433MHz.

Connect the antenna to port 1, calibrate with the included open/short/load standards. The key display is the Smith chart — a perfect 50-ohm antenna sits at the center dot. My first antenna attempt (a quarter-wave whip with no ground plane) showed the impedance way off center.

Adding a proper ground plane (four quarter-wave radials at 45 degrees downward) moved the impedance to about 36 ohms. Shortening the whip slightly moved it to 52 ohms. The return loss display showed S11 of -28dB at 433MHz after tuning — excellent. Practical range improvement over the untuned antenna: about 40% more range in a field test, just from the ground plane and 2mm of wire length.