Getting Started with the NanoVNA H - What I Learned

After spending a few hours with the NanoVNA H, I figured I'd write down what actually stuck. This isn't intended to be a tutorial. My goal was simply to understand enough to begin tuning the telescoping dipole I've been using for weather satellite reception. As I dug into the NanoVNA and worked through the setup, these are the things I came away with.

The reason I bought the NanoVNA wasn't just to own another gadget. I wanted to stop guessing.

My immediate goal is tuning the telescoping dipole I've been using with the 3D printed 120° clip I made for weather satellite reception. Ultimately I'd like to use it to receive Meteor-M No. 2-4 LRPT images with my HackRF and SatDump, but before worrying about satellites I needed to understand the instrument sitting on my bench.

Out of the box the NanoVNA displays several traces at once. There is S11, S21, a Smith Chart and phase information. Rather than trying to understand all of them at once, I disabled everything except S11 LogMag.

From what I understand so far, S11 LogMag is showing how much of the transmitted signal is reflected back from whatever is connected to Port 1. Since tuning an antenna is really about minimizing those reflections at the frequency you're interested in, that became the graph I wanted to focus on.

The other displays are simply different ways of representing RF measurements. The Smith Chart, for example, is displaying impedance graphically. I'll get there eventually, but for now one graph is enough.

Before calibrating anything, I learned that you should first decide what frequencies you're interested in.

For my antenna I set:

• Centre Frequency: 137.5 MHz
• Span: 10 MHz

That gives me a measurement window from approximately 132.5 MHz to 142.5 MHz, which comfortably covers the weather satellite frequencies I'm interested in.

One thing that briefly confused me was entering frequencies. After typing a value the NanoVNA asks whether it's H, k, M or G. It eventually clicked that it was simply asking if I meant Hz, kHz, MHz or GHz.

Calibration

This was probably the biggest takeaway.

Calibration isn't just about the NanoVNA itself. It's about the entire measurement path.

Rather than calibrating directly on the front of the NanoVNA, I left my SMA test cable and coupler attached, then performed the calibration at the end of that assembly.

The supplied standards are easy to identify once you know what they are.

• Open – the connector with the empty centre.
• Short – the all-metal connector.
• Load – the connector with the white insulator containing a precision 50 Ω load.

Work through Open, Short and Load, press Done, then save the calibration.

One thing that still makes me laugh...

It's called SOL calibration, yet you perform Open, Short, Load. Maybe there's a historical reason, but my brain still wants to call it OSL.

The first surprise

Once everything was calibrated I connected my dipole expecting to start tuning.

Instead I discovered something I'd completely forgotten.

The antenna still had its original 75 ohm to 300 ohm television balun attached.

So instead of measuring the antenna itself, I was actually measuring:

NanoVNA - Test Cable - TV Balun - Dipole

That explained why the results weren't quite what I expected.

Rather than modifying it immediately, I think I'm going to leave it exactly as it is and measure it both ways. I have a feeling I'll learn more by understanding what the balun is doing than by simply replacing it.

What I retained

The things that stuck with me were:

• Simplify the display before trying to understand it.
• Decide what frequencies you're actually interested in.
• Calibrate with the measurement cable attached.
• Save the calibration before measuring anything.
• S11 LogMag is the graph I'll probably spend the most time looking at while tuning antennas.
• If the measurements don't make sense, don't assume the NanoVNA is wrong. Check what you've actually connected to it.