By now, most have heard of the passing of Ray Topp, publisher of Radio Guide magazine. I was shocked when I first learned about it in the middle of February. The family has decided to cease publishing the magazine, which is understandable, but also a loss for the industry. The goal of Radio Guide was to provide “real-world technical information.” When I wrote an article, I always thought about the various people I worked with over the years and what they were concerned with.
The last I heard from Ray was the third week in December. He said he had a bout of COVID and there were some complications. He said he was trying very hard to get the January/February 2023 issue done. I sent in my article in early January but never heard anything back, which is unusual. When the publishing date came and went, I thought that perhaps he was still recovering. Unfortunately, that was not so.
My final article for Radio Guide was to be titled: Learning with the Libra VNA
Recently, I pried open my wallet and plunked down the sum of $150.00 for one of these little devices. Now, to be certain, this is not a replacement for a real VNA, especially at a high-power broadcast site. However, it can be used for basic troubleshooting and I have had a good deal of fun fooling around with it.
First, a few quick specifications:
Type: SSA-2N NanoVNA V2.2
Frequency range: 50 KHz to 3 GHz
Power output: -50 to +10 dB
Measurement points: 201 (or 1024 with software and computer)
Measurement types: S11, S12 and S21
Screen Size: 4-inch touch screen
Traces: up to 4
Battery: 3000mAh Lithium Ion
Software OS (VNA-QT): Win 7, Win 10, Linux, MacOS
The unit I purchased came with a small carrying case, calibration loads, and test jumpers. The software is downloadable and easily configured.
What I really like about it is the internal battery and the touch screen.
So what can it be used for?
Test a coaxial cable
Measure the length of a coaxial cable
Figure out what frequency an antenna is designed for
Tune a 1/4 wave stub to make a notch filter
Measure the characteristics of a crystal/holder
Measure a capacitor
Measure an inductor
Tune a parallel resonant LC circuit to make a notch filter
Tune a filter can
Test a high pass, low pass or band pass filter
Sweep an antenna (Simple AM, FM, RPU, STL, WiFi)
Check isocouplers for proper circuit functioning
Pretty much anything you need to know about RF antennas, filters, and transmission lines can be learned with a VNA. One thing to keep in mind; the measurement points are limited, especially in the stand-alone mode. Thus, the smaller the frequency span, the better the measurement resolution will be.
While this is a very inexpensive device designed mainly for Amateur Radio, it can be useful to diagnose antenna and transmission line problems. Would I depend on it to make precise measurements? No. Especially things required by the FCC like base impedance measurements on an AM tower or channel filter measurements for a TV station. Would it work at a high RF transmitter site with multiple AM/FM/TV transmitters? No and chances are you might burn out the front end. Those types of things are best done with professional equipment that has much better accuracy and resolution.
It is a pretty good little tool for basic troubleshooting. One can look at the individual components of an AM ATU for example, or measure the input impedance to see if there has been a shift (should normally be 50 ohms). It is small enough that it can be included in a basic tool kit. It is self-powered. Not bad at all for the price.