NanoVNA – tiny palm size VNA.
NanoVNA-App contains a facility to upload / download NanoVNA flash memory using the DFU bootloader.
The appropriate Windows driver filename is STTub30.sys (or later?) from ST.
Above is a properties list from USBDView of the correct driver.
If you wish to use it, make sure that you have not replaced the bootloader driver with something else. The driver is packaged with ST’s DfuseDemo. Continue reading NanoVNA-App – driver for NanoVNA firmware updates
The article InsertionVSWR of Chinese 1:9 balun module #2 gave a plot of R,X where the reference plane was at the compensation capacitor on the module. Recall that the transformer was actually 1:4.
Ideally you might OSL calibrate the fixture at that point, or at the transformer terminals to obtain a good picture of the transformer response, but it is not convenient to be desoldering the transformer or cutting tracks, so there is a fairly good alternative at the frequencies being discussed (1-30MHz).
Above is an annotated pic of the test setup. The NanoVNA is calibrated at the Port 1 connector (in fact the outboard end of the SMA savers that are never removed), and the desired reference plane is some 32mm away of transmission line of segments of uncertain Zo and loss.
Firstly, the loss will be very low, so we can simply deal with the time delay that the fixture introduces.
The NanoVNA-H4 with DiSlord v1.1.0 firmware has a facility for port extension (though it is not called that, it is called e-delay), as does the NanoVNA-App software used. In both cases, the value of e-delay converted to phase is subtracted from the s11 measurement at each frequency, and the result is correction for the port extension delay.
Note that this:
Let’s apply a temporary short circuit the the compensation capacitor at the reference point.
We want X=0, the rising X is due to the transmission line transformation within the test fixture, and that transformation will render any uncompensated impedance values incorrect (though the ReturnLoss and VSWR will be correct).
Lets look at the phase of s11 for the same case, remembering that the phase of the short circuit should be 180°.
s11 lags 180° by 4.6° @ 30MHz, we can calculate the time equivalent: \(t=\frac{\phi}{2 \pi f}=\frac{4.6 \pi}{360 \pi f}=\frac{4.6}{360 f}=426 \text{e-9s}\), so 426ns is a good starting point for e-delay.
Ok, returning to the R,X chart and adjusting e-delay around 426ns for best X plot…
Above, 430ns is pretty acceptable.
Having backed out the delay of the fixture, lets look at R,X.
Above, R,X with and without the e-delay adjustment. The difference is quite small in this case (the lower R and X @ 30MHz are the e-delay corrected values).
In the experiment above, an X-ACTO #16 knife was used to bridge both sides of the capacitor mentioned. The same technique can be used to bond a track to an adjacent ground track (the knife will cut through the solder mask).
A selection of short circuit coax adapters, M & F, can be very handy when making measurements.
For example, to measure an antenna with a UHF female connector, a short cable with adapters SMA(M) for the VNA to UHF(M) for the antenna can be calibrated with a UHF(F) SC (made simply with a panel jack and the back side shorted with several copper conductors soldered as close to the insulator as possible).
Even if the place where you can conveniently apply the reference SC is not exactly where you want it, if the further extension is something you can characterise well (like a measurable length of known 50Ω line with known VF) you can further tweak the e-delay setting.
For example, to measure an antenna with a UHF female connector on a 400mm pigtail of Belden 8267 (RG213) from its actual feed point, a short cable with adapters SMA(M) for the VNA to UHF(M) for the antenna can be calibrated with a UHF(F) SC. Having found the appropriate e-delay to the applied short circuit, calculate the one-way delay of the coax pigtail. Using TLLC we get 2022ps, so the round trip delay is 4044ps. Now add that 4044ps to the e-delay to the applied short to get the appropriate e-delay to the actual feed point.
The NanoVNA-H4 with DiSlord v1.1.0 firmware has a facility for port extension (though it is not called that, it is called e-delay), as does the NanoVNA-App software used here. In both cases, the value of e-delay converted to phase is subtracted from the s11 measurement at each frequency, and the result is correction for the port extension delay.
Note that this:
The technique may provide a means of moving the reference plane with acceptable accuracy.
This article documents an InsertionVSWR test of another cheap Chinese 1-9 balun purchased for less than <$5 on eBay (shipped).
Above is the advertising pic of the 1-9 balun, it would seem to be a clone of the Noelec 1-9 balun. The balun is a compensated voltage balun with the secondary centre tap grounded for these measurements. Continue reading InsertionVSWR of Chinese 1:9 balun module #2
This documents a running log of hardware related issues in my various NanoVNA devices. Continue reading NanoVNA-H – hardware issues
It has been my experience over more than 50 years that accurate measurements using SMA connectors requires that they be torqued to a consistent and adequate torque. Specifications for brass threads commonly runs around 0.6Nm, and I have a torque wrench calibrated for that torque which I use whenever the connectors are to be properly tightened.
In my NanoVNA-H v3.3, I reinforced the SMA connectors because of a sense that to tighten them to 0.6Nm (5.3inlb) caused the board to flex and over time might crack the tracks (Strength of reinforcement of nanoVNA-H connectors).
Joe Q Smith has an interesting video where he tests some Chinese SMA connectors to destruction, worth watching: NanoVNA Torquing SMA Connectors . In his tests, he needs upwards of 2Nm to damage the cheap Chinese end launch PCB connectors, more than three times the torque I use.
About 6 weeks ago, I took delivery of a new NanoVNA-H4, which as far as I can tell, is a ‘genuine’ Hugyen product.
I did not reinforce the connectors on my new NanoVNA-H4 because there was not the needed clearance for a similar adequate brass bar inside the case.
So, having used a torque wrench at 0.6Nm in the few weeks that I have owned the NanoVNA-H4, the connector on Port 1 failed.
Above, the failed connector has rotated, shearing two of the support pins and tearing the other two off the tracks. Continue reading NanoVNA-H4 v4.3 – broken SMA connector
One of the shortcomings of the NanoVNA-H4 v4.3 is that it is quite easy to drop the SD card inside the case when trying to insert it. Experience is that this is really easy to do in difficult field situations or poor lighting / visibility.
This could have been prevented by better design of the moulded case.
This article describes a simple modification to make it more difficult to miss the card slot.
Above, the modification is a small block of plastic that covers part of the aperture moulded into the case, it projects 1mm into the aperture. Continue reading NanoVNA-H4 v4.3 – improving the SD card slot
This article discusses measuring velocity factor using the NanoVNA. The DUT is coax with N type connectors as it provides a better example to demonstrate and learn from. Having acquired competency, extension to two wire lines is just a matter of attending to the matters of a suitable transformer, and appropriate SOL calibration parts.
The ‘standard’ reference plane on N connectors is shown in the diagram above. For the purpose of this article, length measurements were made between the reference planes at both ends of the cable. Continue reading On testing two wire line loss with an analyser / VNA – part 6
InsertionVSWR of Chinese 1-9 balun module showed a 450Ω load attached to the DUT, and I have been asked to explain further.
Above is the load resistor just visible to the left of the spring terminals on the module. The idea is that the leads need to be very short to avoid unintended / undesired impedance transformation. Continue reading InsertionVSWR of Chinese 1-9 balun module – that load resistor
This article documents an InsertionVSWR test of a cheap Chinese 1-9 balun purchased for less than <$5 on eBay (shipped).
Above is a 1-9 balun, it would seem to be a clone of the Noelec 1-9 balun. The balun is a compensated voltage balun with the secondary centre tap grounded for these measurements. Continue reading InsertionVSWR of Chinese 1-9 balun module
This article series shows how to measure matched line loss (MLL) of a section of two wire line using an analyser or VNA. The examples use the nanoVNA, a low end inexpensive VNA, but the technique is equally applicable to a good vector based antenna analyser of sufficient accuracy (and that can save s1p files).
Article On testing two wire line loss with an analyser / VNA – part 2 showed a 1:1 transformer for measuring two wire lines without encouraging significant common mode current.
Online experts suggest that the required transformer is one from 50Ω to Zo of the line being measured. It is often said that: Continue reading On testing two wire line loss with an analyser / VNA – part 5