Precision measurement for amateurs. DG8SAQ’s VNWA

DG8SAQ VNWA 3 Low Cost 1.3 GHz Vector Network Analyzer | eBay

As you may know, I’m a lover of precision and nice objects. I’m also fond of science, rocket science, RF and electronics.

The Vector Network Analyzer: a must-have

Several years ago, I was discovering the marvellous VNWA measurement device from DG8SAQ, thanks to F6ITU‘s great advice. This device, called a Network Vector Analyzer is a jewel of precision and is really useful for many, many measurements related to radio electronics (And no, it’s not related to IT networks, btw).

DG8SAQ’s Vector Network Analyzer pack, with Calibration Kit and cables.

It enables amateurs like me to acquire for a modest price precision equipment that was previously reserved to big firms only, as second-hand Vector Network Analyzers from manufacturers such as Agilent or Rhode&Schwarz are often sold for over $100k.

Typical eBay item: a second-hand VNA sold for $€130’000.

To give an idea, a classical calibration kit (the small connectors in the wooden box on the photo above) is often sold for over $1500 second-hand on ebay!

More eBay items: second-hand Calibration kits. Way too expensive for me.

So, when DG8SAQ was able to design an affordable VNA, it became an instant success for amateurs all over the world. Even NASA buys them to fit into their rockets, as the device is indirectly able to calculate the inner volume of a container by measuring sent waves, thus allowing the measurement of the remaining liquid propeller gas in the rocket, independently of the position, inclination or speed of the tank. Brilliant! (And that, is applied rocket science!)

So, in 2015 I bought the full package: The VNWA in its carrying case, along with its calibration kit, cables, a GPSDO for GPS-synchonized precision oscillator reference, and even a precisely calibrated Torque wrench needed to screw and unscrew the calibration parts without damaging them or inducing errors in measurement. (Those Swiss customs are detestable, I had to pay import taxes for the Huber+Suhner wrench, although it is manufactured in Switzerland, because the order was from UK…)

Huber+Suhner 110€ wrench…
LeoBodnar GPS Disciplined Oscillator. Feeds the VNWA with a *very* stable clock signal.

This, you may think, is overkill for an amateur. But as I was spending time to get used to the hardware and corresponding software, I discovered more and more uses.

What is a VNWA useful for?

A VNA is sometimes refered as a « *ance-meter », as it can measure very precisely any kind of resistance, inductance, capacitance, reactance etc.

To quote F6ITU, it is also :

  • A HF generator
  • A precision selfmeter
  • A precision milliohm meter
  • A precision capacitance meter
  • A precision frequency meter
  • A precision reflectometer
  • A precision impedancemeter
  • A vector voltmeter (delta U and Phi of two same-frequency signals)
  • An amplitude/frequency/phase signal analyzer
  • An analyzer of unknown components or circuits
  • An antenna analyzer (impedance, resonance, phase, bandwith, harmonics and more)
  • A tool to fine-tune and adapt impedances, including for quartz, saw, cavities etc filters.
  • A tool useful to sort and measure large quantities of quartz components
  • The mandatory add-on to any simulation tool (Qucs, LTSpice, Elsie and more).

The software used to pilot the VNWA (close-source unfortunately) is very complete, but as such needs many days and even weeks to master. You can start with basic measurement, but as you discover the tool, you’ll find more and more subtle options and features that are really only beneficial if you master RF theory. I’m far from understanding every option featured, but it also means that I’m far from being tired of the VNWA, as I learn a bit more each time I turn it on

Aufbau und Test eines Vektor-Netzwerk-Analysator nach DG8SAQ
It gets time to feel at ease with such plots and the multitude options.

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That’s what I call precision!

You may wonder why I wrote « precision » to qualify the device. It’s because it’s insanely precise: The unit is calibrated in tenths of picoseconds(!!), and as an example measurement from the reflectometer mode can calculate cable lengths and issues with a sub-millimeter precision over 60km cables! Same applies for any measurements, as you can imagine.

yes, it’s pico-seconds and nanometers!

Yes, I can proudly say I own a very precise equipment, probably the most precise of my neighborhood. No wonder why calibration kits and torque wrenches are expensive, considering the precision involved. (but not as expensive as Agilent or Rhode&Shwartz equipment).

Additional details

This 2012 video from OZ7OU is still very interesting if you want some details on the inner workings, and the usefulness for measurements.

For my french-speaking followers, I really recommend reading F6ITU’s pages on the Electrolab Wiki. He also translated most of the english tutorials from PA4TIM, which is nice.

I hope you’ll be interested in this marvelous piece of gear!

DG8SAQ
Band-pass Filter measurement. WYSIWYG for electronicians!

1 Comment »

Bruno Kerouanton on août 21st 2020 in Electronics

One Response to “Precision measurement for amateurs. DG8SAQ’s VNWA”

  1. Bruno Kerouanton » A Stratum1 Server at home? responded on 24 Août 2020 at 9:53 #

    […] my former article about the VNWA, I quicky explained that I had acquired a GPS Disciplined Oscillator, as I wanted a […]

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