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A process to cross-reference the NanoVNA with a known excellent antenna Analyzer.

The standard to match is the MFJ-259D. And the mode is SWR (Standing Wave Ratio.)

Without being too technical, the engineering science is simple. The goal is to maximize the amount of power radiated through an antenna into the aether. A way to measure this is the Reflected power fraction of Forward power issued by a transmitter. A ratio of 1.0 is perfect (and very difficult to accomplish.)

In this test, 100′ of RG58 coax cable feed line connected my shack to a POTA Antenna (GRA-1900T Multi-Band HF). The antenna and radials were installed in my back yard.

The frequency important to me is the conventional low power (QRP transmission) point in the 20m band, namely 14.285MHz

After setting the analyzer sweep frequencies (to cover the 20m band), and calibrating the NanoVNA, the process of tuning the antenna began. Too Short, too long, just right… This aspect consists of sweeping the frequency range, stepping out of the shack, changing the antenna length and repeating. The entire changed length ranged less than 3 inches, with the sweet spot at about an inch shorter than ‘too long.’

Time to validate.

At first glance, using the MFJ, it seemed that there might be some calibration error in the Nano VNA. At 50ohms impedance, the MFJ reported antenna resonance at 1.1 SWR at a higher frequency (14.345MHz). This measurement is derived by tuning the analyzer to match a 50ohm load exactly. (The gauge on the right.)

Then it occurred to me that the feed line plus antenna system may not be an ideal load at 50ohms.

So I adjusted the MFJ to find the minimum SWR overall. (The gauge on the left.)

The results show an SWR minimum almost exactly at the frequency the NanoVNA reported after the antenna adjustment process. The resonant goal was 14.285. And the MFJ reported the minimum very close (0.02%) with an impedance of just slightly more than 50ohms.

Special thanks to Gary N6BLU for loaning his analyzer to me to support this validation experiment.