nanovna-H – a ferrite cored test inductor – drilling down on a glitch

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

I have been evaluating one for common tasks around a ham station and noticed a persistent glitch around 7.5MHz in scenarios where |s21| is high.

The nanovna-H has firmware NanoVNA-Q-0.4.3-20f33ba.dfu installed. The nanovna appears to be a nanovna-H v3.3 but it is hard to be sure, it is from China, the land of copyists and fraud. Indeed the nanovna-Q author asserts that genuine nanovna-H have a green overlay whereas mine is blue. Uncertainty is part of the territory!

Above is an example where a ferrite cored inductor similar to an antenna common mode choke is measured, and the underlying curves should be smooth with some random measurement noise. The glitch around 7.5MHz is persistent and much larger than the random noise, so I have investigated further. Continue reading nanovna-H – a ferrite cored test inductor – drilling down on a glitch

nanovna-H – standalone VHF antenna VSWR sweep

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

This article documents a task to perform a VSWR sweep of a VHF antenna stand alone, and to capture the data and screen image for download to a computer.

The nanovna-H has firmware NanoVNA-Q-0.4.3-20f33ba.dfu installed.

The instrument was OSL calibrated for reflection at Port 1 (Ch0 is nanovna speak, convention means little) for 100-500MHz.

A sweep was then performed from 143-149MHz, forcing some interpolation of the calibration data.

The nanovna was configured for VSWR and Smith chart displays, much as you would to use it stand alone.

The sweep was then “Paused”, and the nanovna carried to the computer and plugged into the USB. The power must not be disturbed, the controls must not be altered, the captured data is really just what is frozen on the paused display.

Note that if the thing is unplugged from the USB the nanovna resets and the data is lost, so plug it in properly just once.

I then connected to it using using nanovna MOD v3 and captured the screen, clicked get data once, and saved the .s1p file.

Above is the cropped screen capture. Continue reading nanovna-H – standalone VHF antenna VSWR sweep

nanovna-H – mobile UHF antenna VSWR sweep

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

This article documents a task to perform a VSWR sweep of a UHF mobile antenna.

The nanovna-H has firmware NanoVNA-H_20191018.dfu installed.

The instrument was OSL calibrated for reflection at Port 1 (Ch0 is nanovna speak, convention means little) for 100-500MHz.

A sweep was then performed from 400-470MHz, forcing some interpolation of the calibration data.

The nanovna was configured for VSWR and Smith chart displays, much as you would to use it stand alone, but I did have it attached to the computer to capure the display (it seems it cannot be saved for later playback).

Above, the captured display. The results are pretty much as expected, no surprises there. Continue reading nanovna-H – mobile UHF antenna VSWR sweep

nanovna-H – a ferrite cored test inductor

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

This article documents some tests using a small ferrite cored test inductor that provides a similar impedance to that of a common mode choke suited to HF antenna feed lines.

The nanovna-H has firmware NanoVNA-H_20191018.dfu installed.

A small fixture was OSL calibrated and impedance measured by reflection (ie s11).

The results broadly reconcile with previous measurements of the inductor, but the jitter is worth of examination.

Above is a chart from nanovna-saver showing the measured impedance components, we might expect a reasonably smooth curve for each. It has a lot of jitter on it, and you might excuse that as a result of applying the instrument and method to such a high impedance… but for two things: Continue reading nanovna-H – a ferrite cored test inductor

nanovna-H – first experience

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

It is a semi open source project, some information is published in open access places like unrestricted github and currently unrestricted acccess messages in a io.groups forum, but the wiki and files collection of that forum is by membership only and so is not publicly available.

After reviewing a lot of public information, I chose to try  purchase an Nanovna-H. There were trials along the way in that Hugen79’s preferred supplier on Alibaba could not accept my suburb in the address, so I searched eBay, Amazon and Aliexpress for items that appears to be a Nanovna-H. On the day, eBay and Amazon had no listings, but there were some on Aliexpress.

In this case, though the seller lied about material things, it does appear that I received a ‘genuine’ nanovna-H, and one of very recent manufacture as it had firmware dated two days after I placed the order.

The device was charged and needed only an hour to reach full charge, it was about 75% charged. No grief with the battery manager stuck in shutdown (yet) as some users report.

Above, the nanovna-H as received. Continue reading nanovna-H – first experience

nanovna-H – occasional glitches in measured data

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

I purchased what appears to be a ‘genuine’ nanovna-H and it has firmware NanoVNA-H_20191018.dfu installed. During checkout of the delivered device, an issue became evident, an issue worth describing in its own article.

Glitches on the displayed data are occasional, but hardly rare, and are a concern.

The nanovna was OSL calibrated (is for reflection only) from 1 to 500MHz and the cal save in C4.

On repeated scans of the SC used for the cal, there are obvious occasional glitches evident on various PC clients.

Above is nanovnasharp v1.03. An expanded scale shows the observation, an occasional single measurement, always with a downwards glitch  of |S11|dB of variable magnitude, but usually less than a couple of dB. Continue reading nanovna-H – occasional glitches in measured data

RG6/U with CCS centre conductor at HF

at Series match for a half wave dipole I mentioned that RG6/U may have a copper clad steel (CCS) centre conductor, and may have significantly more loss at HF than expected based on datasheets and calculators.

Above is a comparison of matched line loss based on measurement of a length of RG6/U Quad Shield CCS cable and prediction from Simsmith of Belden 8215 (also CCS). The ripple is due to measurement system error. Continue reading RG6/U with CCS centre conductor at HF

Series match for a half wave dipole

An online poster was demonstrating the effect of varying line length on a half wave dipole on VSWR(50) and by mistake configured the line be of of Zo=75Ω.

He asked the question

In the general case, if you are trying to match 50 Ohms, would you be better off feeding a normal backyard dipole with 75 Ohm coax if you are willing to prune it to a specific length after the fact?

Continue reading Series match for a half wave dipole

Rigexpert AA-600 reference plane

The Rigexpert AA-600 has an inbuilt calibration which is convenient to use. It is capable of OSL calibration, but this article discusses only the inbuilt calibration.

The reference plane is the plane at which the instrument calibration is correct, at other locations there is a transmission line impedance transformation applied.

The pic above shows the reference plane, but where exactly is it and why do you want to know? Continue reading Rigexpert AA-600 reference plane

nanoVNA MOD v3 – a first look

Since I have a nanovna-H coming on a ‘slow boat from China’, whilst working with a Touchstone s1p file exported from Rigexpert’s Antscope I tried to open the file in nanoVNA MOD v3.

Above, the outcome was not good. The name of the loaded file is not shown, there were no messages during loading, and an empty graph and the stimulus data does not match the file. Continue reading nanoVNA MOD v3 – a first look