Hams wanting to resolve an antenna system problem often seek the advice of the assembled experts on social media of one form or another.
They are often advised by many that “you need an NanoVNA”… no matter what they have described, no matter their own capabilities.
Now if they follow that path, it might be the beginning of wonderful things, or it might be a huge frustration.
The problem is that although the NanoVNA is relatively low cost for its capability, affordable to lots of hams, and arguably it can replace whatever they were using previously, but… the requisite knowledge does not come in the box.
There was a generation of “antenna analysers” that were effectively one port VNAs with fixed calibration that provided capability to sweep an antenna system over a frequency range of interest and give a graphical presentation of VSWR, and not a lot of learning required to exploit the thing. (Yes, some of them also provided for a custom SOL calibration).
These type of instruments are still of great utility, though considerably more expensive that the NanoVNA. I have used a Rigexpert AA-600 extensively, but cannot recommend any Rigexpert product, or more generally any current product in this category.
A possible solution
Is there a way to leverage to capability of the NanoVNA to replace the scanning antenna analyser?
This article describes a solution for very common NanoVNA-H4 hardware with SD card, and NanoVNA-D v1.2.40 firmware. The solution may not work for other hardware and firmware.
So, the objective is to simplify the interface to present just a VSWR curve as shown above.
So here is a setup procedure.
Procedure
WARNING: this procedure will overwrite some of all data existing on the NanoVNA, do not proceed unless you accept this.
Power the NanoVNA OFF, wait a few seconds and Power ON.
Using the menu, clear the configuration.
Now perform the screen calibration and when you have happy with it, save the configuration.
Perform a SOL calibration at the NanoVNA jack over a suitable frequency range. If you are interested only in 1.8 to 30MHz, calibrate for 1-41MHz using 401 steps. If you want to cover 54MHz as well, calibrate for 1-101MHz.
Save the calibration into Slot 0 (the default read on power up.)
Now go into the menu and disable Trace 1 through 3.
Configure Trace 0 for VSWR, set reference position to 0 and scale to 0.2/div.
Check the display, and if it is correct, using the calibration menu save the calibration again to Slot 0 (you do not have to recalibrate, this step will simply overlay the new display setup on the existing calibration data set.)
So, if you have done all this properly, you should be able to power cycle the NanoVNA and it should start with the new display setup and sweep range.
Using it
So, to use it, use the menus to set the Stimulus Start and Stop to suit the range you wish to measure, eg 7.0-7.3MHz as in the example shown earlier. The NanoVNA will interpolate the calibration data set, and your 401 point scan from 7.0-7.3MHz should capture quite narrow / detailed artifacts.
More advanced
There are two methods for loading a configuration without going through the menus. Either of these can be useful for recalling a configuration quickly, accurately and conveniently.
The NanoVNA has a serial console command interface which can be accessed using Teraterm over the USB cable. For this exercise, I used Teraterm5 which allows setting delays after each character and after each line so that the NanoVNA is not overrun.
Above, the Teraterm serial port setup.
trace 0 swr s11 trace 0 scale 0.2 trace 0 refpos 0 trace 1 smith s11 trace 1 rx trace 1 scale 1 trace 1 refpos 0 trace 2 r s11 trace 2 scale 20 trace 2 refpos 0 trace 3 x s11 trace 3 scale 20 trace 3 refpos 4 trace 1 off trace 2 off trace 3 off
The above command script can be copied and pasted into the Teraterm terminal window, and played into the console. This command script also configures the other three traces for antenna measurements and turns them off for a simple display of VSWR only… but they can be easily enabled from the menu when desired. NanoVNA setup for common antenna system measurement tasks show the use of the additional traces.
Another option is to save the command script above to a file on the NanoVNA’s SD card, eg VswrOnly.cmd (extension MUST be cmd). It can be “loaded” from the menu: /MENU/CONFIG/EXPERT SETTINGS/MORE/LOAD COMMAND SCRIPT.
Conclusions
The NanoVNA can be configured to power up with a simplified display showing just a VSWR sweep well suited to lots of antenna measurement tasks, and this configuration might be more convenient to many NanoVNA users.