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

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

nanoVNA – a first plunge

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

It is not really a project as such, but a loose collection of hardware versions manufactured in variously compliant forms, and several PC and web clients competing for space. Information is partly in the public domain, partly in restricted access forums where the controller’s identity is hidden… the modern way of ham radio.

After some research, and with some residual uncertainty, I decided upon the so-called nanoVNA-H design by Hugen79

Hugen79 nominates a seller on Alibaba, but I was unable to purchase there because it would not accept my suburb in an address, and unwilling to put at risk the minimal buyer protection by purchasing outside of the selling platform, I went to Aliexpress for sellers. (No listings on eBay or Amazon for AU account holders, but many listings have appears on eBay since purchase).

Aliexpress is a platform by the Chinese for the Chinese, and from experience I am too well aware of the high risk of scammers and cheats leading to loss of one’s money. I decided to exceed my self imposed limit of A$30, a risk management strategy, and spend the $85 required by a seller offering free returns (whatever that means).

Above is the pic from the seller’s listing. Continue reading nanoVNA – a first plunge

Cooking the books on VSWR – Bird43 indication

A reader of Cooking the books on VSWR asked

…so you are telling me that I could measure this Prev>Pfwd with a directional wattmeter like my Bird43… I have never seen it and I don’t believe it.

For clarification, I did not discuss Prev or Pfwd in respect of the three scenarios (other than to say Pref cannot exceed Pfwd).

I did discuss line voltage measurements you can make with a simple RF volt meter which was in the article’s reference quote. But, let’s discuss what you might measure by inserting a 50Ω Bird43 directional wattmeter in the Load case 2 scenario.

Above is a calculated plot of the expected Pfwd and -Prev readings, Prev is shown negated so you can add it by eye with Pfwd to obtain the net power Power (blue line). Continue reading Cooking the books on VSWR – Bird43 indication

Cooking the books on VSWR

Having recently seen the suggestion that …

Most tools and most derivations of SWR will produce negative SWR reports because they are more interested in mathematics than in measurements you can make with a simple RF volt meter.

…, this article explores the expected voltage on a practical transmission line under two mismatch scenarios, voltage that ought be measurable with a simple RF voltmeter.

VSWR concepts… by the book

Textbooks on transmission lines often introduce the concept of standing waves by presenting a plot of voltage along a mismatched lossless transmission line.

Above is a plot of calculated line voltage vs displacement from the load, -ve is towards the source. Continue reading Cooking the books on VSWR

Noise Figure – Equivalent Noise Bandwidth

Harald Friis (Friis 1944) gave guidance on measuring the noise figure of receivers, and explains the concept of Effective Bandwidth.

Effective Bandwidth

The contribution to the available output noise by the Johnson-noise sources in the signal generator is readily calculated for and ideal or square-top band-pass characteristic and it is GKTB where B is the bandwidth in cycles per second. In practice, however, the band is not flat; ie, the gain over the band is not constant but varies with frequency. In this case the total contribution is ∫GfKTdf where Gf is the gain at frequency f. The effective bandwidth B of the network is defined as the bandwidth of an ideal band-pass network with gain G that gives this contribution to the noise output.

Continue reading Noise Figure – Equivalent Noise Bandwidth

nanovna-saver – a first look

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

I have long held the view that these things are most useful when accompanied by a capable PC client that performs flexible text book presentations of data.

Considering buying one, my first step was to perform a desk evaluation of a popular PC client, which seems to be nanovna-saver.

Before downloading it, I examined the first screenshot on the github page.

It gives evidence that the author does not follow industry standard convention for transmission line terms and theory.

In the results shown above (s11) impedance is 39.105+j39.292Ω and some transformations of that value. Continue reading nanovna-saver – a first look