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

Antenna analyser – what if the device under test does not have a coax plug on it?

I have written a few articles on fixtures for adapting the device under test (DUT) to an antenna analyser’s coax jack.

Antenna analysers come with a range of connectors, the UHF connector is very popular, perhaps less so are N-type, SMA and BNC.

I use a range of fixtures made to suit specific applications, but the most flexible are the two shown in the following pic.

Above are two adapters: Continue reading Antenna analyser – what if the device under test does not have a coax plug on it?

Post post implementation review R134a replaced with HyChill Minus 30

I repaced the R134a refrigerant in my car aircon system with a hydrocarbon refrigerant, Hychill Minus 30 (HC-30).

Research had indicated that permeation of reduced barrier hoses was problem with HC refrigerants. The hoses in the car were Goodyear hoses with catalogue numbers, but I was unable to find data on them. Their diameter was comparable to standard barrier hoses, so I proceeded with the trial. Continue reading Post post implementation review R134a replaced with HyChill Minus 30

Diagnosing a possible antenna problem by comparison with a baseline

Recently I have had difficult reaching the local DMR repeater on 70cm, and needed to check that the antenna system had not deteriorated.

I took a baseline measurement with an AA-600 after some refurbishment work in Jan 2018, and was able to compare a current sweep to that baseline.

Above, a wide Return Loss sweep of the Diamond X-50N with feed line compared to the baseline (the thin blue line). Continue reading Diagnosing a possible antenna problem by comparison with a baseline

Do Distortionless Lines exist?

I am asked about my use of the term Distortionless Lines from time to time, often in the vein of they don’t exist, so why discuss them?

Concept

The concept derives from the work of Heaviside and others in seeking a solution to distortion in long telegraph lines.

The problem was that digital telegraph pulses were distorted due to different attenuation and propagation time for different components of the square waves.

Heaviside proposed that transmission lines could be modelled as distributed resistance (R), inductance (L), conductance (G) and capacitance (C) elements.

In each incremental length Δx, there is incremental R, L, G and C. Continue reading Do Distortionless Lines exist?